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CPCS 203
Student Name: _____________________________
Lab sheet 5
Section: __
King Abdulaziz University
Faculty of Computing and Information Systems
Spring Term 2012/1433
Course Code: CPCS-203
Course Name: Programming II
_________________________________________________________________
Objectives
In this chapter you will learn:
 How exception and error handling works.
 To use try, throw and catch to detect, indicate and handle exceptions, respectively.
 To use the finally block to release resources.
 How stack unwinding enables exceptions not caught in one scope to be caught in
another scope.
 How stack traces help in debugging.
 How exceptions are arranged in an exception class hierarchy.
 To declare new exception classes.
 To create chained exceptions that maintains complete stack trace information.
 What files are and how they are used to retain application data between successive
executions.
 To create, read, write and update files.
 To use class File to retrieve information about files and directories.
 The Java input/output stream class hierarchy.
 The differences between text files and binary files.
 Sequential-access file processing.
 To use classes Scanner and Formatter to process text files.
 To use classes FileInputStream and FileOutputStream to read from and write to files.
 To use classes ObjectInputStream and ObjectOutputStream to read objects from and
write objects to files.
 To use a JFileChooser dialog.
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CPCS 203
Student Name: _____________________________
Lab sheet 5
Section: __
Prelab Activity:
Programming Output
For each of the given program segments, read the code and write the output in the space provided below each
program. [Note: Do not execute these programs on a computer.]
1. What is output by the following application?
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public class Test
{
public static String lessThan100( int number ) throws Exception
{
if ( number >= 100 )
throw new Exception( "Number too large." );
}
return String.format( "The number %d is less than 100", number );
public static void main( String args[] )
{
try
{
System.out.println( lessThan100( 1 ) );
System.out.println( lessThan100( 22 ) );
System.out.println( lessThan100( 100 ) );
System.out.println( lessThan100( 11 ) );
}
catch( Exception exception )
{
System.out.println( exception.toString() );
}
} // end main method
} // end class Test
Your answer:
The number 1 is less than 100
The number 22 is less than 100
java.lang.Exception: Number too large.
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CPCS 203
Student Name: _____________________________
2. What is output by the following program?
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public class Test
{
public static void method3() throws RuntimeException
{
throw new RuntimeException( "RuntimeException occurred in method3" );
}
public static void method2() throws RuntimeException
{
try
{
method3();
}
catch ( RuntimeException exception )
{
System.out.printf( "The following exception occurred in method2\n%s\n",
exception.toString() );
throw exception;
}
} // end method2
public static void method1() throws RuntimeException
{
try
{
method2();
}
catch ( RuntimeException exception )
{
System.out.printf( "The following exception occurred in method1\n%s\n",
exception.toString() );
throw exception;
}
} // end method1
public static void main( String args[] )
{
try
{
method1();
}
catch ( RuntimeException exception )
{
System.out.printf( "The following exception occurred in main\n%s\n",
exception.toString() );
}
} // end main
} // end class test
Your answer:
The following exception occurred in method2
java.lang.RuntimeException: RuntimeException occurred in method3
The following exception occurred in method1
java.lang.RuntimeException: RuntimeException occurred in method3
The following exception occurred in main
java.lang.RuntimeException: RuntimeException occurred in method3
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Lab sheet 5
Section: __
CPCS 203
Student Name: _____________________________
3. What is output by the following program?
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public class Test
{
public static String divide( int number1, int number2 )
{
return String.format( "%d divided by %d is %d",
number1, number2, ( number1 / number2 ) );
}
public static void main( String args[] )
{
try
{
System.out.println( divide( 4, 2 ) );
System.out.println( divide( 20, 5 ) );
System.out.println( divide( 100, 0 ) );
}
catch( Exception exception )
{
System.out.println( exception.toString() );
}
} // end main
} // end class Test
Your answer:
4 divided by 2 is 2
20 divided by 5 is 4
java.lang.ArithmeticException: / by zero
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Lab sheet 5
Section: __
CPCS 203
Student Name: _____________________________
Lab sheet 5
Section: __
4. What is output by the following program if the user enters the values 3 and 4.7?
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import javax.swing.JOptionPane;
public class Test
{
public static String sum( int num1, int num2 )
{
return String.format( "%d + %d = %d", num1, num2, ( num1 + num2 ) );
}
public static void main( String args[] )
{
int number1;
int number2;
try
{
number1 =
Integer.parseInt( JOptionPane.showInputDialog( "Enter an integer: " ) );
number2 = Integer.parseInt(
JOptionPane.showInputDialog( "Enter another integer: " ) );
System.out.println( sum( number1, number2 ) );
}
catch ( NumberFormatException numberFormatException )
{
System.out.println( numberFormatException.toString() );
}
} // end main method
} // end class Test
Your answer:
java.lang.NumberFormatException: For input string: "4.7"
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CPCS 203
Student Name: _____________________________
Lab sheet 5
Section: __
Prelab Activity:
Correct the Code
Determine if there is an error in each of the following program segments. If there is an error,
specify whether it is a logic error or a compilation error, circle the error in the program and write
the corrected code in the space provided after each problem. If the code does not contain an
error, write “no error.” [Note: There may be more than one error in each program segment.]
5. The following code segment should catch only NumberFormatExceptions and display an error message dialog if such an exception occurs:
catch ( Exception exception )
JOptionPane.showMessageDialog( this,
"A number format exception has occurred",
"Invalid Number Format", JOptionPane.ERROR_MESSAGE );
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Your answer:
catch ( NumberFormatException numberFormatException )
{
JOptionPane.showMessageDialog( this,
"A number format exception has occurred",
"Invalid Number Format", JOptionPane.ERROR_MESSAGE );
}
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•
•
The catch handler should declare that it catches NumberFormatExceptions. This is a logic error.
The body of the catch handler must be enclosed in braces. This is a syntax error.
6. In the following code segment, assume that method1 can throw both NumberFormatExceptions and
ArithmeticExceptions. The following code segment should provide appropriate exception handlers for
each exception type and should display an appropriate error message dialog in each case:
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try
method1();
catch ( NumberFormatException n, ArithmeticException a )
{
JOptionPane.showMessageDialog( this,
String.format( "The following exception occurred\n%s\n%s\n",
n.toString(), a.toSting() ),
"Exception occurred", JOptionPane.ERROR_MESSAGE );
}
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CPCS 203
Student Name: _____________________________
Lab sheet 5
Section: __
Your answer:
try
{
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method1();
}
catch ( NumberFormatException n )
{
JOptionPane.showMessageDialog( this,
"The following exception occurred \n" + n.toString(),
"Exception occurred", JOptionPane.ERROR_MESSAGE );
}
catch ( ArithmeticException a )
{
JOptionPane.showMessageDialog( this,
"The following exception occurred \n" + a.toString(),
"Exception occurred", JOptionPane.ERROR_MESSAGE );
}
•
The code in the try block must be enclosed in braces. This is a syntax error.
•
Each catch handler can handle only one type of exception, so each must be declared separately. This is a
syntax error.
7. The following code segment should display an error message dialog if the user does not enter two integers:
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try
{
}
int number1 =
Integer.parseInt( JOptionPane.showInputDialog( "Enter first integer:" ) );
int number2 =
Integer.parseInt( JOptionPane.showInputDialog( "Enter second integer:" ) );
JOptionPane.showMessageDialog( this, "The sum is: " + ( number1 + number2 ) );
Your answer:
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try
{
int number1 =
Integer.parseInt( JOptionPane.showInputDialog( "Enter first integer:" ) );
int number2 =
Integer.parseInt( JOptionPane.showInputDialog( "Enter second integer:" ) );
JOptionPane.showMessageDialog( this, "The sum is: " + ( number1 + number2 ) );
}
catch ( NumberFormatException numberFormatException )
{
JOptionPane.showMessageDialog( this, numberFormatException, );
"Exception occurred", JOptionPane.ERROR_MESSAGE );
}
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CPCS 203
Student Name: _____________________________
•
•
Lab sheet 5
Section: __
A try block must be followed by either a catch handler or a finally block (as a minimum). This is a
syntax error.
A catch handler must be declared to catch the NumberFormatException and display the error message
dialog.
Determine if there is an error in each of the following program segments. If there is an error,
specify whether it is a logic error or a compilation error, circle the error in the program and write
the corrected code in the space provided after each problem. If the code does not contain an
error, write “no error.” [Note: There may be more than one error in each program segment.]
8. The following code segment should open a file for object output:
ObjectOutputStream output =
new ObjectOutputStream( new FileOutput( "file.dat" ) );
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Your answer:
ObjectOutputStream output =
new ObjectOutputStream( new FileOutputStream( "file.dat" ) );
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FileOutput
is not a class in the java.io package. The proper class to use here is FileOutputStream.
Compilation error.
9. The following code segment should open a file for object input:
FileInputStream input = new FileInputStream( "file.dat" );
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Your answer:
ObjectInputStream input = new ObjectInputStream( new FileInputStream( "file.dat" ) );
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Although a FileInputStream can be used to read bytes from a file, it does not provide any object input
capabilities. This requires the FileInputStream to be wrapped in an ObjectInputStream object, which
enables a program to read objects from a stream. Logic error.
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CPCS 203
Student Name: _____________________________
Lab sheet 5
Section: _
10. The following code segment should write the object named record into a file. Assume that output is a
prop- erly defined object of class ObjectOutputStream.
output.writeObject( record );
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Your answer:
output.writeObject( record );
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The proper method name for writing an object is writeObject, not write . Compilation error.
11. The following code segment should open a text file for reading with a Scanner.
Scanner input = new Scanner( "myfile.txt" );
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Your answer:
Scanner input = new Scanner( new File( "myfile.txt" ) );
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• To open a file for reading with class
the
Scanner constructor.
Scanner,
you must supply a File object as the argument to
12. The following code segment should open a text file for writing with a Formatter.
Formatter output = new Formatter();
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Your answer:
Formatter output = new Formatter( "myfile.txt" );
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To open a text file for writing with class Formatter, you must supply the file name as the
argument to the Formatter constructor. This can be done with just the name of the file as a
string or by passing an object of class File.
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CPCS 203
Student Name: _____________________________
Lab sheet 5
Section: _
Lab Exercises:
Lab Exercise — Access Array
The following problem is intended to be solved in a closed-lab session with a teaching assistant or instructor
present. The problem is divided into six parts:
1. Lab Objectives
2. Description of the Problem
3. Sample Output
4. Program Template (Fig. L 11.1–Fig. L 11.3)
5. Problem-Solving Tips
6. Follow-Up Question and Activity
The program template represents a complete working Java program with one or more key lines of code replaced
with comments. Read the problem description and examine the sample output, then study the template code.
Using the problem-solving tips as a guide, replace the /* */ comments with Java code. Compile and execute the
program. Compare your output with the sample output provided. Then answer the follow-up question. The
source code for the template is available at www.pearsonhighered.com/deitel.
Lab Objectives
This lab was designed to reinforce programming concepts from Chapter 11 of Java How to Program: 8/e. In this
lab, you will practice:
•
Using exception handling to determine valid inputs.
•
Using exception handling to write more robust and more fault-tolerant programs.
The follow-up question and activity also will give you practice:
•
Creating your own exception type and throwing exceptions of that type.
Description of the Problem
Write a program that allows a user to input integer values into a 10-element array and search the array. The program should allow the user to retrieve values from the array by index or by specifying a value to locate. The program should handle any exceptions that might arise when inputting values or accessing array elements. The
program should throw a NumberNotFoundException (Fig. L 11.1) if a particular value cannot be found in the
array during a search. If an attempt is made to access an element outside the array bounds, catch the ArrayIndexOutOfBoundsException and display an appropriate error message. Also, the program should throw an ArrayIndexOutOfBoundsException if an attempt is made to access an element for which the user has not yet input a
value.
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CPCS 203
Student Name: _____________________________
Sample Output
Program Template
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// NumberNotFoundException.java
public class NumberNotFoundException extends Exception
{
// no-argument constructor specifies default error message
public NumberNotFoundException()
{
super( "Number not found in array" );
}
}
// constructor to allow customized error message
public NumberNotFoundException( String message )
{
super( message );
}
// end class NumberNotFoundException
Fig. L 5.1 |
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NumberNotFoundException.java.
// ArrayAccess.java
import java.awt.FlowLayout;
import java.awt.GridLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.JFrame;
Fig. L 5.2 |
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ArrayAccess.java.
(Part 1 of 4.)
Lab sheet 5
Section: _
CPCS 203
Student Name: _____________________________
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import
import
import
import
javax.swing.JLabel;
javax.swing.JOptionPane;
javax.swing.JPanel;
javax.swing.JTextField;
public class ArrayAccess extends JFrame
{
private JTextField inputField;
private JTextField retrieveField1;
private JTextField retrieveField2;
private JTextField outputField;
private JPanel inputArea;
private JPanel retrieveArea;
private JPanel outputArea;
private
private
private
private
int num;
int index = 0;
int array[] = new int[ 10 ];
String result;
// set up GUI
public ArrayAccess()
{
super( "Accessing Array values" );
setLayout( new FlowLayout() );
// set up input Panel
inputArea = new JPanel();
inputArea.add( new JLabel( "Enter array elements here" ) );
inputField = new JTextField( 10 );
inputArea.add( inputField );
inputField.addActionListener(
new ActionListener()
{
public void actionPerformed( ActionEvent e )
{
/* Create a try block in which the application reads the number
entered in the inputField and assigns it to the next index
in the array, then increments instance variable index. */
/* Write catch handlers that catch the two types of exceptions
that the previous try block might throw (NumberFormatException
and ArrayIndexOutOfBoundsException), and display appropriate
messages in error message dialogs. */
inputField.setText( "" );
} // end method actionPerformed
} // end anonymous inner class
); // end call to addActionListener
// set up retrieve Panel
retrieveArea = new JPanel( new GridLayout( 2, 2 ) );
retrieveArea.add( new JLabel( "Enter number to retrieve" ) );
retrieveField1 = new JTextField( 10 );
retrieveArea.add( retrieveField1 );
Fig. L 5.2 |
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ArrayAccess.java.
(Part 2 of 4.)
Lab sheet 5
Section: _
CPCS 203
Student Name: _____________________________
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Fig. L 5.2 |
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Lab sheet 5
Section: _
retrieveField1.addActionListener(
new ActionListener()
{
public void actionPerformed( ActionEvent event )
{
/* Create a try block in which the application reads from
retrieveField1 the number the user wants to find in the
array, then searches the current array contents for the number.
If the number is found, the outputField should display all the
indices in which the number was found. If the number is not
found, a NumberNotFoundException should be thrown. */
/* Write catch handlers that
the try block might throw
NumberNotFoundException),
in error message dialogs.
catch the two types of exceptions that
(NumberFormatException and
and display appropriate messages
*/
retrieveField1.setText( "" );
} // end method actionPerformed
} // end anonymous inner class
); // end call to addActionListener
retrieveArea.add( new JLabel( "Enter index to retrieve" ) );
retrieveField2 = new JTextField( 10 );
retrieveArea.add( retrieveField2 );
retrieveField2.addActionListener(
new ActionListener()
{
public void actionPerformed( ActionEvent event )
{
/* Create a try block in which the application reads from
retrieveField2 the index of a value in the array, then
displays the value at that index in the outputField. If the index
input by the user is not a number a NumberFormatException should
be thrown. If the number input by the user is outside the array
bounds or represents an element in which the application has not
stored a value, an ArrayIndexOutOfBoundsException should
be thrown. */
/* Write catch handlers that catch the two types of exceptions
the try block might throw (NumberFormatException and
ArrayIndexOutOfBoundsException), and display appropriate
messages in error message dialogs. */
retrieveField2.setText( "" );
} // end anonymous inner class
} // end new ActionListener
); // end call to addActionListener
// set up output Panel
outputArea = new JPanel();
outputArea.add( new JLabel( "Result" ) );
outputField = new JTextField( 30 );
outputField.setEditable( false );
outputArea.add( outputField );
ArrayAccess.java.
(Part 3 of 4.)
CPCS 203
Student Name: _____________________________
Lab sheet 5
Section: _
118
add( inputArea );
119
add( retrieveArea );
120
add( outputArea );
121
} // end constructor
122 } // end class ArrayAccess
Fig. L 11.2 |
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ArrayAccess.java.
(Part 4 of 4.)
// ArrayAccessTest.java
import javax.swing.JFrame;
public class ArrayAccessTest
{
// execute application
public static void main( String args[] )
{
ArrayAccess application = new ArrayAccess();
application.setDefaultCloseOperation( JFrame.EXIT_ON_CLOSE );
application.setSize( 400, 200 );
application.setVisible( true );
}
} // end class ArrayAccessTest
Fig. L 5.3 |
ArrayAccessTest.java.
Problem-Solving Tips
1. When you search the array for a value, you should define a boolean value at the beginning of the try block
and initialize it to false. If the value is found in the array, set the boolean value to true. This will help you
determine whether you need to throw an exception due to a search key that is not found.
2. Refer to the sample output to decide what messages to display in the error dialogs.
3. Each of the three event handlers will have its own try statement.
4. If you have any questions as you proceed, ask your lab instructor for assistance.
Solution
[Note: Since only class ArrayAccess was modified, we show only that file here.]
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// ArrayAccess.java
import java.awt.FlowLayout;
import java.awt.GridLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JOptionPane;
import javax.swing.JPanel;
import javax.swing.JTextField;
public class ArrayAccess extends JFrame
{
private JTextField inputField;
private JTextField retrieveField1;
private JTextField retrieveField2;
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CPCS 203
Student Name: _____________________________
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private JTextField outputField;
private JPanel inputArea;
private JPanel retrieveArea;
private JPanel outputArea;
private
private
private
private
int num;
int index = 0;
int array[] = new int[ 10 ];
String result;
// set up GUI
public ArrayAccess()
{
super( "Accessing Array values" );
setLayout( new FlowLayout() );
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// set up input Panel
inputArea = new JPanel();
inputArea.add( new JLabel( "Enter array elements here" ) );
inputField = new JTextField( 10 );
inputArea.add( inputField );
inputField.addActionListener(
new ActionListener()
{
public void actionPerformed( ActionEvent e )
{
try
{
num = Integer.parseInt( inputField.getText() );
array[ index ] = num; // place value in array
index++;
}
catch ( NumberFormatException formatException )
{
JOptionPane.showMessageDialog( null,
"Please enter only integer values",
"Invalid Input", JOptionPane.ERROR_MESSAGE );
}
catch ( ArrayIndexOutOfBoundsException outOfBounds )
{
JOptionPane.showMessageDialog( null,
"Array may contain only 10 elements",
"Array Full", JOptionPane.ERROR_MESSAGE );
}
inputField.setText( "" );
} // end method actionPerformed
} // end anonymous inner class
); // end call to addActionListener
// set up retrieve Panel
retrieveArea = new JPanel( new GridLayout( 2, 2 ) );
retrieveArea.add( new JLabel( "Enter number to retrieve" ) );
retrieveField1 = new JTextField( 10 );
retrieveArea.add( retrieveField1 );
retrieveField1.addActionListener(
new ActionListener()
{
Lab sheet 5
Section: _
CPCS 203
Student Name: _____________________________
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Lab sheet 5
Section: _
public void actionPerformed( ActionEvent event )
{
try
{
num = Integer.parseInt( retrieveField1.getText() );
boolean found = false;
result = String.format(
"%d was in the following fields of the array: ", num );
16 | P a g e
for ( int i = 0; i < index; i++ )
{
if ( num == array[ i ] )
{
result += String.format( "%d ", i );
found = true;
} // end if
} // end for
if ( found == false )
throw new NumberNotFoundException();
outputField.setText( result );
} // end try
catch ( NumberFormatException formatException )
{
JOptionPane.showMessageDialog( null,
"Please enter only integer values",
"Invalid Input", JOptionPane.ERROR_MESSAGE );
} // end catch
catch ( NumberNotFoundException numberException )
{
JOptionPane.showMessageDialog( null, numberException.getMessage(),
"Not Found", JOptionPane.ERROR_MESSAGE );
} // end catch
retrieveField1.setText( "" );
} // end method actionPerformed
} // end anonymous inner class
); // end call to addActionListener
retrieveArea.add( new JLabel( "Enter index to retrieve" ) );
retrieveField2 = new JTextField( 10 );
retrieveArea.add( retrieveField2 );
retrieveField2.addActionListener(
new ActionListener()
{
public void actionPerformed( ActionEvent event )
{
try
{
num = Integer.parseInt( retrieveField2.getText() );
if ( num >= index || num < 0 )
throw new ArrayIndexOutOfBoundsException( "Index Not Found." );
outputField.setText( String.format(
"The number at index %d is %d", num, array[ num ] ) );
} // end try
CPCS 203
Student Name: _____________________________
Lab sheet 5
Section: _
133
catch ( NumberFormatException formatException )
134
{
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JOptionPane.showMessageDialog( null,
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"Array indices must be integer values",
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"Invalid Input", JOptionPane.ERROR_MESSAGE );
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} // end catch
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catch ( ArrayIndexOutOfBoundsException outOfBounds )
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{
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JOptionPane.showMessageDialog( null, outOfBounds.getMessage(),
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"Index Out of Bounds", JOptionPane.ERROR_MESSAGE );
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} // end catch
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retrieveField2.setText( "" );
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} // end anonymous inner class
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} // end new ActionListener
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); // end call to addActionListener
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// set up output Panel
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outputArea = new JPanel();
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outputArea.add( new JLabel( "Result" ) );
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outputField = new JTextField( 30 );
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outputField.setEditable( false );
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outputArea.add( outputField );
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add( inputArea );
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add( retrieveArea );
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add( outputArea );
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} // end constructor
161 } // end class ArrayAccess
Follow-Up Question and Activity
1.
Create another exception class called DuplicateValueException that will be thrown if the user inputs a
value that already resides in the array. Modify your lab exercise solution to use this new exception class to
indicate when a duplicate value is input, in which case an appropriate error message should be displayed.
The program should continue normal execution after handling the exception.
Solution
[Note: We show only the new and modified files here.]
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// DuplicateValueException.java
public class DuplicateValueException extends NumberFormatException
{
public DuplicateValueException()
{
super( "Integer can not be a duplicate." );
}
}
public DuplicateValueException( String message )
{
super( message );
}
// end class OverflowException
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CPCS 203
Student Name: _____________________________
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// ArrayAccess.java
import java.awt.FlowLayout;
import java.awt.GridLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JOptionPane;
import javax.swing.JPanel;
import javax.swing.JTextField;
public class ArrayAccess extends JFrame
{
private JTextField inputField;
private JTextField retrieveField1;
private JTextField retrieveField2;
private JTextField outputField;
private JPanel inputArea;
private JPanel retrieveArea;
private JPanel outputArea;
private
private
private
private
int num;
int index = 0;
int array[] = new int[ 10 ];
String result;
// set up GUI
public ArrayAccess()
{
super( "Accessing Array values" );
setLayout( new FlowLayout() );
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// set up input Panel
inputArea = new JPanel();
inputArea.add( new JLabel( "Enter array elements here" ) );
inputField = new JTextField( 10 );
inputArea.add( inputField );
inputField.addActionListener(
new ActionListener()
{
public void actionPerformed( ActionEvent e )
{
try
{
num = Integer.parseInt( inputField.getText() );
// determine whether num is a duplicate
for ( int i = 0; i < index; i++ )
{
if ( num == array[ i ] )
throw new DuplicateValueException();
} // end for
array[ index ] = num; // place value in array
index++;
}
catch ( DuplicateValueException duplicateValueException )
{
Lab sheet 5
Section: _
CPCS 203
Student Name: _____________________________
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JOptionPane.showMessageDialog( null,
"Please enter only unique integers",
"Duplicate Value", JOptionPane.ERROR_MESSAGE );
}
catch ( NumberFormatException formatException )
{
JOptionPane.showMessageDialog( null,
"Please enter only integer values",
"Invalid Input", JOptionPane.ERROR_MESSAGE );
}
catch ( ArrayIndexOutOfBoundsException outOfBounds )
{
JOptionPane.showMessageDialog( null,
"Array may contain only 10 elements",
"Array Full", JOptionPane.ERROR_MESSAGE );
}
19 | P a g e
inputField.setText( "" );
} // end method actionPerformed
} // end anonymous inner class
); // end call to addActionListener
// set up retrieve Panel
retrieveArea = new JPanel( new GridLayout( 2, 2 ) );
retrieveArea.add( new JLabel( "Enter number to retrieve" ) );
retrieveField1 = new JTextField( 10 );
retrieveArea.add( retrieveField1 );
retrieveField1.addActionListener(
new ActionListener()
{
public void actionPerformed( ActionEvent event )
{
try
{
num = Integer.parseInt( retrieveField1.getText() );
boolean found = false;
result = String.format(
"%d was in the following fields of the array: ", num );
for ( int i = 0; i < index; i++ )
{
if ( num == array[ i ] )
{
result += String.format( "%d ", i );
found = true;
} // end if
} // end for
if ( found == false )
throw new NumberNotFoundException();
outputField.setText( result );
} // end try
catch ( NumberFormatException formatException )
{
JOptionPane.showMessageDialog( null,
"Please enter only integer values",
"Invalid Input", JOptionPane.ERROR_MESSAGE );
} // end catch
Lab sheet 5
Section: _
CPCS 203
Student Name: _____________________________
Lab sheet 5
Section: _
118 catch ( NumberNotFoundException numberException )
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{
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JOptionPane.showMessageDialog( null, numberException.getMessage(),
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"Not Found", JOptionPane.ERROR_MESSAGE );
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} // end catch
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retrieveField1.setText( "" );
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} // end method actionPerformed
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} // end anonymous inner class
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); // end call to addActionListener
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retrieveArea.add( new JLabel( "Enter index to retrieve" ) );
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retrieveField2 = new JTextField( 10 );
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retrieveArea.add( retrieveField2 );
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retrieveField2.addActionListener(
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new ActionListener()
134
{
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public void actionPerformed( ActionEvent event )
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{
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try
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{
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num = Integer.parseInt( retrieveField2.getText() );
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if ( num >= index || num < 0 )
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throw new ArrayIndexOutOfBoundsException( "Index Not Found." );
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outputField.setText( String.format(
145
"The number at index %d is %d", num, array[ num ] ) );
146
} // end try
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catch ( NumberFormatException formatException )
148
{
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JOptionPane.showMessageDialog( null,
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"Array indices must be integer values",
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"Invalid Input", JOptionPane.ERROR_MESSAGE );
152
} // end catch
153
catch ( ArrayIndexOutOfBoundsException outOfBounds )
154
{
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JOptionPane.showMessageDialog( null, outOfBounds.getMessage(),
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"Index Out of Bounds", JOptionPane.ERROR_MESSAGE );
157
} // end catch
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retrieveField2.setText( "" );
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} // end anonymous inner class
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} // end new ActionListener
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); // end call to addActionListener
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// set up output Panel
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outputArea = new JPanel();
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outputArea.add( new JLabel( "Result" ) );
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outputField = new JTextField( 30 );
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outputField.setEditable( false );
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outputArea.add( outputField );
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add( inputArea );
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add( retrieveArea );
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add( outputArea );
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} // end constructor
175 } // end class ArrayAccess
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CPCS 203
Student Name: _____________________________
Lab sheet 5
Section: _
Lab Exercises:
Lab Exercise 2 — Employee Hierarchy with Object Serialization
This problem is intended to be solved in a closed-lab session with a teaching assistant or instructor present. The
problem is divided into six parts:
1. Lab Objectives
2. Description of the Problem
3. Sample Output
4. Program Template (Fig. L 5.4–Fig. L 5.5)
5. Problem-Solving Tips
6. Follow-Up Questions and Activities
The program template represents a complete working Java program with one or more key lines of code replaced
with comments. Read the problem description and examine the sample output; then study the template code.
Using the problem-solving tips as a guide, replace the /* */ comments with Java code. Compile and execute the
program. Compare your output with the sample output provided. The source code for the template is available
at www.pearsonhighered.com/deitel.
Lab Objectives
This lab was designed to reinforce programming concepts from Chapter 17 of Java How to Program: 8/e. In this
lab you will practice:
•
•
Modifying a class hierarchy to ensure that objects of the classes in the hierarchy are Serializable.
Opening a file for output.
•
Writing objects to a file.
The follow-up questions and activities will also give you practice:
•
Opening a file for input.
•
Reading objects to a file.
•
Reading and writing entire arrays of Serializable objects.
Problem Description
Modify the Employee hierarchy from Figs. 10.4–10.8 to enable serialization of the classes in the hierarchy. Then,
modify the application of Fig. 10.9 to output each object in the array employees to a file using object
serialization. [Note: In the follow-up questions, you will be asked to read these objects from the file created
here.]
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CPCS 203
Student Name: _____________________________
Lab sheet 5
Section: _
Sample Output
Employees processed individually:
salaried employee: John Smith
social security number: 111-11-1111
weekly salary: $800.00
earned: $800.00
hourly employee: Karen Price
social security number: 222-22-2222
hourly wage: $16.75; hours worked: 40.00
earned: $670.00
commission employee: Sue Jones
social security number: 333-33-3333
gross sales: $10,000.00; commission rate: 0.06
earned: $600.00
base-salaried commission employee: Bob Lewis
social security number: 444-44-4444
gross sales: $5,000.00; commission rate: 0.04; base salary: $300.00
earned: $500.00
Template
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// Lab Exercise 1: Employee.java
// Employee abstract superclass.
/* import the Serializable interface */
/* modify the following class to make all objects of its subclasses Serializable */
public abstract class Employee
{
private String firstName;
private String lastName;
private String socialSecurityNumber;
// three-argument constructor
public Employee( String first, String last, String ssn )
{
firstName = first;
lastName = last;
socialSecurityNumber = ssn;
} // end three-argument Employee constructor
// set first name
public void setFirstName( String first )
{
firstName = first;
} // end method setFirstName
// return first name
public String getFirstName()
{
return firstName;
} // end method getFirstName
Fig. L 5.4 |
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Employee
abstract superclass. (Part 1 of 2.)
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// set last name
public void setLastName( String last )
{
lastName = last;
} // end method setLastName
// return last name
public String getLastName()
{
return lastName;
} // end method getLastName
// set social security number
public void setSocialSecurityNumber( String ssn )
{
socialSecurityNumber = ssn; // should validate
} // end method setSocialSecurityNumber
// return social security number
public String getSocialSecurityNumber()
{
return socialSecurityNumber;
} // end method getSocialSecurityNumber
// return String representation of Employee object
public String toString()
{
return String.format( "%s %s\nsocial security number: %s",
getFirstName(), getLastName(), getSocialSecurityNumber() );
} // end method toString
// abstract method overridden by subclasses
public abstract double earnings(); // no implementation here
} // end abstract class Employee
Fig. L 5.4 |
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Lab sheet 5
Section: _
Employee
abstract superclass. (Part 2 of 2.)
// Lab Exercise 1: OutputEmployees.java
// Employee hierarchy test program.
/* import the java.io package classes necessary for writing objects into a file */
public class OutputEmployees
{
public static void main( String args[] )
{
// create subclass objects
SalariedEmployee salariedEmployee =
new SalariedEmployee( "John", "Smith", "111-11-1111", 800.00 );
HourlyEmployee hourlyEmployee =
new HourlyEmployee( "Karen", "Price", "222-22-2222", 16.75, 40 );
CommissionEmployee commissionEmployee =
new CommissionEmployee(
"Sue", "Jones", "333-33-3333", 10000, .06 );
Fig. L 17.2 |
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Employee
class hierarchy test program. (Part 1 of 2.)
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Lab sheet 5
Section: _
BasePlusCommissionEmployee basePlusCommissionEmployee =
new BasePlusCommissionEmployee(
"Bob", "Lewis", "444-44-4444", 5000, .04, 300 );
System.out.println( "Employees processed individually:\n" );
System.out.printf( "%s\n%s: $%,.2f\n\n",
salariedEmployee, "earned", salariedEmployee.earnings() );
System.out.printf( "%s\n%s: $%,.2f\n\n",
hourlyEmployee, "earned", hourlyEmployee.earnings() );
System.out.printf( "%s\n%s: $%,.2f\n\n",
commissionEmployee, "earned", commissionEmployee.earnings() );
System.out.printf( "%s\n%s: $%,.2f\n\n",
basePlusCommissionEmployee,
"earned", basePlusCommissionEmployee.earnings() );
// create four-element Employee array
Employee employees[] = new Employee[ 4 ];
// initialize
employees[ 0
employees[ 1
employees[ 2
employees[ 3
]
]
]
]
array with Employees
= salariedEmployee;
= hourlyEmployee;
= commissionEmployee;
= basePlusCommissionEmployee;
System.out.println( "Output the elements of the array:\n" );
/* Write code here that opens the file EmployeeData.ser for object output then
writes all the elements of the array employees into the file */
} // end main
} // end class OutputEmployees
Fig. L 5.5 |
Employee
class hierarchy test program. (Part 2 of 2.)
Problem-Solving Tips
1. To write objects with an ObjectOutputStream, the objects’ class(es) must implement interface Serializable . You can do this for all objects in the Employee hierarchy by simply implementing the Serializable interface in the superclass Employee. Then, the Serializable relationship is inherited into all
of class Employee’s subclasses.
2. Code related to processing object streams might throw exceptions for many reasons. All IOExceptions
are checked exceptions, so these exceptions must be caught or your program will not compile.
3. If you have any questions as you proceed, ask your lab instructor for assistance.
Solution
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// Fig. 10.4: Employee.java
// Employee abstract superclass.
import java.io.Serializable;
public abstract class Employee implements Serializable
{
private String firstName;
private String lastName;
private String socialSecurityNumber;
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// three-argument constructor
public Employee( String first, String last, String ssn )
{
firstName = first;
lastName = last;
socialSecurityNumber = ssn;
} // end three-argument Employee constructor
// set first name
public void setFirstName( String first )
{
firstName = first;
} // end method setFirstName
// return first name
public String getFirstName()
{
return firstName;
} // end method getFirstName
// set last name
public void setLastName( String last )
{
lastName = last;
} // end method setLastName
// return last name
public String getLastName()
{
return lastName;
} // end method getLastName
// set social security number
public void setSocialSecurityNumber( String ssn )
{
socialSecurityNumber = ssn; // should validate
} // end method setSocialSecurityNumber
// return social security number
public String getSocialSecurityNumber()
{
return socialSecurityNumber;
} // end method getSocialSecurityNumber
// return String representation of Employee object
public String toString()
{
return String.format( "%s %s\nsocial security number: %s",
getFirstName(), getLastName(), getSocialSecurityNumber() );
} // end method toString
// abstract method overridden by subclasses
public abstract double earnings(); // no implementation here
} // end abstract class Employee
25 | P a g e
Lab sheet 5
Section: _
CPCS 203
Student Name: _____________________________
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// Lab Exercise 1: OutputEmployees.java
// Employee hierarchy test program.
import java.io.FileOutputStream;
import java.io.ObjectOutputStream;
import java.io.IOException;
public class OutputEmployees
{
public static void main( String args[] )
{
// create subclass objects
SalariedEmployee salariedEmployee =
new SalariedEmployee( "John", "Smith", "111-11-1111", 800.00 );
HourlyEmployee hourlyEmployee =
new HourlyEmployee( "Karen", "Price", "222-22-2222", 16.75, 40 );
CommissionEmployee commissionEmployee =
new CommissionEmployee(
"Sue", "Jones", "333-33-3333", 10000, .06 );
BasePlusCommissionEmployee basePlusCommissionEmployee =
new BasePlusCommissionEmployee(
"Bob", "Lewis", "444-44-4444", 5000, .04, 300 );
System.out.println( "Employees processed individually:\n" );
System.out.printf( "%s\n%s: $%,.2f\n\n",
salariedEmployee, "earned", salariedEmployee.earnings() );
System.out.printf( "%s\n%s: $%,.2f\n\n",
hourlyEmployee, "earned", hourlyEmployee.earnings() );
System.out.printf( "%s\n%s: $%,.2f\n\n",
commissionEmployee, "earned", commissionEmployee.earnings() );
System.out.printf( "%s\n%s: $%,.2f\n\n",
basePlusCommissionEmployee,
"earned", basePlusCommissionEmployee.earnings() );
// create four-element Employee array
Employee employees[] = new Employee[ 4 ];
// initialize
employees[ 0
employees[ 1
employees[ 2
employees[ 3
try
{
]
]
]
]
array with Employees
= salariedEmployee;
= hourlyEmployee;
= commissionEmployee;
= basePlusCommissionEmployee;
ObjectOutputStream output =
new ObjectOutputStream( new FileOutputStream( "EmployeeData.ser" ) );
for ( Employee currentEmployee : employees )
output.writeObject( currentEmployee );
}
catch ( IOException exception )
{
exception.printStackTrace();
}
} // end main
} // end class OutputEmployees
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Lab sheet 5
Section: _
CPCS 203
Student Name: _____________________________
Lab sheet 5
Section: _
Follow-Up Questions and Activities
1. Modify the application of Fig. 10.9 to read the objects in the file EmployeeData.ser into an array called
employees, then output the contents of the array polymorphically as in Fig. 10.9.
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// Lab Exercise 1, Follow-Up 1: InputEmployees.java
// Employee hierarchy test program.
import java.io.FileInputStream;
import java.io.ObjectInputStream;
import java.io.IOException;
import java.lang.ClassNotFoundException;
public class InputEmployees
{
public static void main( String args[] )
{
// create four-element Employee array
Employee employees[] = new Employee[ 4 ];
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try
{
ObjectInputStream input =
new ObjectInputStream( new FileInputStream( "EmployeeData.ser" ) );
for ( int i = 0; i < employees.length; i++ )
employees[ i ] = ( Employee ) input.readObject();
}
catch ( ClassNotFoundException cnfException )
{
cnfException.printStackTrace();
}
catch ( IOException ioException )
{
ioException.printStackTrace();
}
System.out.println( "Employees processed polymorphically:\n" );
// generically process each element in array employees
for ( Employee currentEmployee : employees )
{
System.out.println( currentEmployee ); // invokes toString
// determine whether element is a BasePlusCommissionEmployee
if ( currentEmployee instanceof BasePlusCommissionEmployee )
{
// downcast Employee reference to
// BasePlusCommissionEmployee reference
BasePlusCommissionEmployee employee =
( BasePlusCommissionEmployee ) currentEmployee;
double oldBaseSalary = employee.getBaseSalary();
employee.setBaseSalary( 1.10 * oldBaseSalary );
System.out.printf(
"new base salary with 10%% increase is: $%,.2f\n",
employee.getBaseSalary() );
} // end if
CPCS 203
Student Name: _____________________________
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Lab sheet 5
Section: _
System.out.printf(
"earned $%,.2f\n\n", currentEmployee.earnings() );
} // end for
// get type name of each object in employees array
for ( int j = 0; j < employees.length; j++ )
System.out.printf( "Employee %d is a %s\n", j,
employees[ j ].getClass().getName() );
} // end main
} // end class InputEmployees
Employees processed polymorphically:
salaried employee: John Smith
social security number: 111-11-1111
weekly salary: $800.00
earned $800.00
hourly
social
hourly
earned
employee: Karen Price
security number: 222-22-2222
wage: $16.75; hours worked: 40.00
$670.00
commission employee: Sue Jones
social security number: 333-33-3333
gross sales: $10,000.00; commission rate: 0.06
earned $600.00
base-salaried commission employee: Bob Lewis
social security number: 444-44-4444
gross sales: $5,000.00; commission rate: 0.04; base salary: $300.00
new base salary with 10% increase is: $330.00
earned $530.00
Employee
Employee
Employee
Employee
0
1
2
3
is
is
is
is
a
a
a
a
SalariedEmployee
HourlyEmployee
CommissionEmployee
BasePlusCommissionEmployee
2. Since arrays are objects in Java, entire arrays of Serializable objects can be output simply by passing an
array’s name to an ObjectOutputStream’s writeObject method. Similarly, an entire array of Serializable
objects can be read with a single call to an ObjectInputStream’s readObject method. Modify class OutputEmployees from Lab Exercise 1 to write the entire array to the file with a single output statement. Then, modify class InputEmployees from Follow-Up Exercise 1 to read the entire array with a single statement.
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// Lab Exercise 1, Follow-Up 2: OutputEmployees.java
// Employee hierarchy test program.
import java.io.FileOutputStream;
import java.io.ObjectOutputStream;
import java.io.IOException;
public class OutputEmployees
{
public static void main( String args[] )
28 | P a g e
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Lab sheet 5
Section: _
// create subclass objects
SalariedEmployee salariedEmployee =
new SalariedEmployee( "John", "Smith", "111-11-1111", 800.00 );
HourlyEmployee hourlyEmployee =
new HourlyEmployee( "Karen", "Price", "222-22-2222", 16.75, 40 );
CommissionEmployee commissionEmployee =
new CommissionEmployee(
"Sue", "Jones", "333-33-3333", 10000, .06 );
BasePlusCommissionEmployee basePlusCommissionEmployee =
new BasePlusCommissionEmployee(
"Bob", "Lewis", "444-44-4444", 5000, .04, 300 );
System.out.println( "Employees processed individually:\n" );
System.out.printf( "%s\n%s: $%,.2f\n\n",
salariedEmployee, "earned", salariedEmployee.earnings() );
System.out.printf( "%s\n%s: $%,.2f\n\n",
hourlyEmployee, "earned", hourlyEmployee.earnings() );
System.out.printf( "%s\n%s: $%,.2f\n\n",
commissionEmployee, "earned", commissionEmployee.earnings() );
System.out.printf( "%s\n%s: $%,.2f\n\n",
basePlusCommissionEmployee,
"earned", basePlusCommissionEmployee.earnings() );
// create four-element Employee array
Employee employees[] = new Employee[ 4 ];
// initialize
employees[ 0
employees[ 1
employees[ 2
employees[ 3
try
{
]
]
]
]
array with Employees
= salariedEmployee;
= hourlyEmployee;
= commissionEmployee;
= basePlusCommissionEmployee;
ObjectOutputStream output =
new ObjectOutputStream( new FileOutputStream( "EmployeeData.ser" ) );
output.writeObject( employees );
}
catch ( IOException exception )
{
exception.printStackTrace();
}
} // end main
} // end class OutputEmployees
// Lab Exercise 1, Follow-Up 2: InputEmployees.java
// Employee hierarchy test program.
import java.io.FileInputStream;
import java.io.ObjectInputStream;
import java.io.IOException;
import java.lang.ClassNotFoundException;
public class InputEmployees
{
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Student Name: _____________________________
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public static void main( String args[] )
{
// create four-element Employee array
Employee employees[] = new Employee[ 4 ];
try
{
ObjectInputStream input =
new ObjectInputStream( new FileInputStream( "EmployeeData.ser" ) );
employees = ( Employee[] ) input.readObject();
}
catch ( ClassNotFoundException cnfException )
{
cnfException.printStackTrace();
}
catch ( IOException ioException )
{
ioException.printStackTrace();
}
System.out.println( "Employees processed polymorphically:\n" );
// generically process each element in array employees
for ( Employee currentEmployee : employees )
{
System.out.println( currentEmployee ); // invokes toString
// determine whether element is a BasePlusCommissionEmployee
if ( currentEmployee instanceof BasePlusCommissionEmployee )
{
// downcast Employee reference to
// BasePlusCommissionEmployee reference
BasePlusCommissionEmployee employee =
( BasePlusCommissionEmployee ) currentEmployee;
double oldBaseSalary = employee.getBaseSalary();
employee.setBaseSalary( 1.10 * oldBaseSalary );
System.out.printf(
"new base salary with 10%% increase is: $%,.2f\n",
employee.getBaseSalary() );
} // end if
System.out.printf(
"earned $%,.2f\n\n", currentEmployee.earnings() );
} // end for
// get type name of each object in employees array
for ( int j = 0; j < employees.length; j++ )
System.out.printf( "Employee %d is a %s\n", j,
employees[ j ].getClass().getName() );
} // end main
} // end class InputEmployees
30 | P a g e
Lab sheet 5
Section: _
CPCS 203
Student Name: _____________________________
Employees processed polymorphically:
salaried employee: John Smith
social security number: 111-11-1111
weekly salary: $800.00
earned $800.00
hourly
social
hourly
earned
employee: Karen Price
security number: 222-22-2222
wage: $16.75; hours worked: 40.00
$670.00
commission employee: Sue Jones
social security number: 333-33-3333
gross sales: $10,000.00; commission rate: 0.06
earned $600.00
base-salaried commission employee: Bob Lewis
social security number: 444-44-4444
gross sales: $5,000.00; commission rate: 0.04; base salary: $300.00
new base salary with 10% increase is: $330.00
earned $530.00
Employee
Employee
Employee
Employee
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is
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a
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a
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HourlyEmployee
CommissionEmployee
BasePlusCommissionEmployee
Lab sheet 5
Section: _
CPCS 203
Student Name: _____________________________
Lab sheet 5
Section: _
Lab Exercises:
Lab Exercise 3 — Debugging
The program in this section does not compile. Fix all the syntax errors, so that the program will
compile success- fully. Once the program compiles, execute the program, and compare the output
with the sample output. Then eliminate any logic errors that may exist. The sample output
demonstrates what the program’s output should be once the program’s code is corrected. The
source code is available at the Web sites www.pearsonhighered.com/ deitel.
Sample Output
SpecialIOException: Special IO Exception Occurred
Broken Code
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import java.io.IOException;
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// Debugging Chapter 11: DebugException.java
import java.io.IOException;
public class SpecialIOException throws IOException
{
public SpecialIOException()
{
super( "Special IO Exception Occurred" );
}
}
public SpecialIOException( String message )
{
this( message );
}
// end class SpecialIOException
public class DebugException
{
public static void main( String args[] )
{
try
{
throw new SpecialIOException();
}
catch ( Exception exception )
{
System.err.println( exception.toString() );
}
catch ( IOException ioException )
{
System.err.println( ioException.toString() );
}
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}
Lab sheet 5
Section: _
catch ( SpecialIOException specialIOException )
{
specialIOException.toString();
}
} // end method main
// end class DebugException
Solution
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import java.io.IOException;
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// Debugging solution Chapter 14: DebugException.java
import java.io.IOException;
public class SpecialIOException extends IOException
{
public SpecialIOException()
{
super( "Special IO Exception Occurred" );
}
}
public SpecialIOException(String message)
{
super( message );
}
// end class SpecialIOException
public class DebugException
{
public static void main( String args[] )
{
try
{
throw new SpecialIOException();
}
catch ( SpecialIOException specialIOException )
{
System.err.println( specialIoException.toString() );
}
catch ( IOException ioException )
{
System.err.println( ioException.toString() );
}
catch ( Exception exception )
{
System.err.println( exception.toString() );
}
} // end method main
} // end class DebugException
List of Errors:
•
The keyword throws should be replaced with extends in the first line of class
Compilation error.
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SpecialIOException.
CPCS 203
Student Name: _____________________________
•
•
•
Lab sheet 5
Section: _
The second constructor of class SpecialIOException calls itself recursively. It should call the superclass
constructor by using the keyword super rather than the keyword this. Compilation error.
In class DebugException the exception handlers following the try block should be listed in subclass to
superclass order (i.e., SpecialIOException, IOException and Exception). Compilation error.
The SpecialIOException catch handler does not actually output an error message. Place the call to toString in a System.err.println statement to output the information to the user. Logic error.
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CPCS 203
Student Name: _____________________________
Lab sheet 5
Section: _
Postlab Activities
Coding Exercises
These coding exercises reinforce the lessons learned in the lab and provide additional programming experience
outside the classroom and laboratory environment. They serve as a review after you have successfully completed
the Prelab Activities and Lab Exercises.
For each of the following problems, write a program or a program segment that performs the specified action:
1. Define a class InvalidInputException. This class should be a direct subclass of Exception. It should specify
the default message "Your input was invalid.", but should also enable the programmer to specify a custom
message as well.
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// Coding Exercise 1: InvalidInputException.java
public class InvalidInputException extends Exception
{
public InvalidInputException()
{
super( "Your input was invalid" );
}
}
public InvalidInputException( String message )
{
super( message );
}
// end class InvalidInputException
2. Define a class ExceptionTest based on class DivideByZeroWithExceptionHandling of Fig. 11.2 of Java
How To Program: 8/e. Not only should ExceptionTest check for division by zero and valid integer input, it
should also ensure that the integers being input are positive. If they are not, it should throw an InvalidInputException (using the class from Coding Exercise 1) with the message "You must enter positive numbers". The program should catch this exception and display an error message.
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// Coding Exercise 2: ExceptionTest.java
// An exception-handling example that checks for divide-by-zero.
import java.util.InputMismatchException;
import java.util.Scanner;
public class ExceptionTest
{
// demonstrates throwing an exception when a divide-by-zero occurs
public static int quotient( int numerator, int denominator )
throws ArithmeticException
{
return numerator / denominator; // possible division by zero
} // end method quotient
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Student Name: _____________________________
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Lab sheet 5
Section: _
public static void main( String args[] )
{
Scanner scanner = new Scanner( System.in ); // scanner for input
boolean continueLoop = true; // determines if more input is needed
do
{
try // read two numbers and calculate quotient
{
System.out.print( "Please enter an integer numerator: " );
int numerator = scanner.nextInt();
System.out.print( "Please enter an integer denominator: " );
int denominator = scanner.nextInt();
if ( ( numerator < 0 ) || ( denominator < 0 ) )
throw new InvalidInputException( "You must enter positive numbers" );
int result = quotient( numerator, denominator );
System.out.printf( "\nResult: %d / %d = %d\n", numerator,
denominator, result );
continueLoop = false; // input successful; end looping
} // end try
catch ( InvalidInputException invalidInputException )
{
System.err.println( invalidInputException );
System.out.println( "Please try again.\n" );
}
catch ( InputMismatchException inputMismatchException )
{
System.err.println( inputMismatchException );
scanner.nextLine(); // discard input so user can try again
System.out.println(
"You must enter integers. Please try again.\n" );
} // end catch
catch ( ArithmeticException arithmeticException )
{
System.err.println( arithmeticException );
System.out.println(
"Zero is an invalid denominator. Please try again.\n" );
} // end catch
} while ( continueLoop ); // end do...while
} // end main
} // end class ExceptionTest
36 | P a g e
CPCS 203
Student Name: _____________________________
Lab sheet 5
Section: _
These coding exercises reinforce the lessons learned in the lab and provide additional programming experience
outside the classroom and laboratory environment. They serve as a review after you have successfully completed
the Prelab Activities and Lab Exercises.
For each of the following problems, write a program or a program that performs the specified action(s).
3. Create a simple sequential-access file-processing program that might be used by professors to help manage
their student records. For each student, the program should obtain an ID number, the student’s first name,
the student’s last name and the student’s grade. The data obtained for each student constitutes a record for
the student and should be stored in an object of a class called Student. The program should save the records in a file specified by the user.
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// Coding Exercise 1: Student.java
// A class that represents one record of student information.
public class Student
{
private int studentID;
private String firstName;
private String lastName;
private double grade;
// no-argument constructor calls other constructor with default values
public Student()
{
this( 0, "", "", 0.0 ); // call four-argument constructor
} // end no-argument Student constructor
// initialize a record
public Student( int id, String first, String last, double grade )
{
setStudentID( id );
setFirstName( first );
setLastName( last );
setGrade( grade );
} // end four-argument Student constructor
// set student ID number
public void setStudentID( int id )
{
studentID = id;
} // end method setStudentID
// get student ID number
public int getStudentID()
{
return studentID;
} // end method getStudentID
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Student Name: _____________________________
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// set first name
public void setFirstName( String first )
{
firstName = first;
} // end method setFirstName
// get first name
public String getFirstName()
{
return firstName;
} // end method getFirstName
// set last name
public void setLastName( String last )
{
lastName = last;
} // end method setLastName
// get last name
public String getLastName()
{
return lastName;
} // end method getLastName
// set grade
public void setGrade( double gradeValue )
{
grade = gradeValue;
} // end method setGrade
// get grade
public double getGrade()
{
return grade;
} // end method getGrade
} // end class Student
// Coding Exercise 1: CreateTextFile.java
// Writing data to a text file with class Formatter.
import java.io.FileNotFoundException;
import java.lang.SecurityException;
import java.util.Formatter;
import java.util.FormatterClosedException;
import java.util.NoSuchElementException;
import java.util.Scanner;
public class CreateTextFile
{
private Formatter output; // used to output text to file
private Scanner input; // used to input text from the instructor
// enable user to open file
public void openFile()
{
try
{
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Lab sheet 5
Section: _
CPCS 203
Student Name: _____________________________
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input = new Scanner( System.in );
System.out.println(
"Enter the name of the file in which to store student records:" );
// read the file name and use it to create a Formatter object
output = new Formatter( input.nextLine() );
} // end try
catch ( SecurityException securityException )
{
System.err.println(
"You do not have write access to this file." );
System.exit( 1 );
} // end catch
catch ( FileNotFoundException filesNotFoundException )
{
System.err.println( "Error creating file." );
System.exit( 1 );
} // end catch
} // end method openFile
// add records to file
public void addRecords()
{
// object to be written to file
Student record = new Student();
39 | P a g e
System.out.printf( "%s\n%s\n%s\n%s\n\n",
"To terminate input, type the end-of-file indicator ",
"when you are prompted to enter input.",
"On UNIX/Linux/Mac OS X type <ctrl> d then press Enter",
"On Windows type <ctrl> z then press Enter" );
System.out.printf( "%s\n? ",
"Enter student ID number (> 0), first name, last name and grade:" );
while ( input.hasNext() ) // loop until end-of-file indicator
{
try // output values to file
{
// retrieve data to be output
record.setStudentID( input.nextInt() ); // read student ID number
record.setFirstName( input.next() ); // read first name
record.setLastName( input.next() ); // read last name
record.setGrade( input.nextDouble() ); // read grade
if ( record.getStudentID() > 0 )
{
// write new record
output.format( "%d %s %s %.2f\n", record.getStudentID(),
record.getFirstName(), record.getLastName(),
record.getGrade() );
} // end if
else
{
System.out.println(
"Student ID number must be greater than 0." );
} // end else
} // end try
Lab sheet 5
Section: _
CPCS 203
Student Name: _____________________________
78
catch ( FormatterClosedException formatterClosedException )
79
{
80
System.err.println( "Error writing to file." );
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return;
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} // end catch
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catch ( NoSuchElementException elementException )
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{
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System.err.println( "Invalid input. Please try again." );
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input.nextLine(); // discard input so user can try again
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} // end catch
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} // end while
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} // end method addRecords
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// close file
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public void closeFile()
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{
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if ( output != null )
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output.close();
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} // end method closeFile
100 } // end class CreateTextFile
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// Coding Exercise 1: CreateTextFileTest.java
// Testing the CreateTextFile class.
public class CreateTextFileTest
{
public static void main( String args[] )
{
CreateTextFile application = new CreateTextFile();
application.openFile();
application.addRecords();
application.closeFile();
} // end main
} // end class CreateTextFileTest
Enter the name of the file in which to store student records:
students.txt
To terminate input, type the end-of-file indicator
when you are prompted to enter input.
On UNIX/Linux/Mac OS X type <ctrl> d then press Enter
On Windows type <ctrl> z then press Enter
Enter student ID number
? 1 Suzy Green 88.6
Enter student ID number
? 2 Jessica Purple 98.3
Enter student ID number
? 3 Paul Orange 75.9
Enter student ID number
? ^Z
40 | P a g e
(> 0), first name, last name and grade:
(> 0), first name, last name and grade:
(> 0), first name, last name and grade:
(> 0), first name, last name and grade:
Lab sheet 5
Section: _
CPCS 203
Student Name: _____________________________
Lab sheet 5
Section: _
4. Create a simple sequential-access file-processing program to complement the program in Coding Exercise 1.
This program should open the file created by the Coding Exercise 1 program and read and display the grade
information for each student. The program should also display the class average.
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// Coding Exercise 2: ReadTextFile.java
// This program reads a text file and displays each record and
// displays the class average.
import java.io.File;
import java.io.FileNotFoundException;
import java.lang.IllegalStateException;
import java.util.NoSuchElementException;
import java.util.Scanner;
public class ReadTextFile
{
private Scanner input;
// enable user to open file
public void openFile()
{
try
{
Scanner tempScanner = new Scanner( System.in );
System.out.println(
"Enter the name of the file containing the student records:" );
String fileName = tempScanner.nextLine();
input = new Scanner( new File( fileName ) );
} // end try
catch ( FileNotFoundException fileNotFoundException )
{
System.err.println( "Error opening file." );
System.exit( 1 );
} // end catch
} // end method openFile
// read record from file
public void readRecords()
{
// object to be written to screen
Student record = new Student();
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double total = 0; // stores total of all grades
int gradeCounter = 0; // counts grades input
System.out.printf( "\n%-12s%-12s%-12s%10s\n", "Student ID",
"First Name", "Last Name", "Grade" );
try // read records from file using Scanner object
{
while ( input.hasNext() )
{
record.setStudentID( input.nextInt() ); // read account number
record.setFirstName( input.next() ); // read first name
record.setLastName( input.next() ); // read last name
record.setGrade( input.nextDouble() ); // read balance
CPCS 203
Student Name: _____________________________
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// display record contents
System.out.printf( "%-12d%-12s%-12s%10.2f\n",
record.getStudentID(), record.getFirstName(),
record.getLastName(), record.getGrade() );
++gradeCounter;
total += record.getGrade();
} // end while
System.out.printf(
"\nClass average is: %.2f\n", ( total / gradeCounter ) );
} // end try
catch ( NoSuchElementException elementException )
{
System.err.println( "File improperly formed." );
input.close();
System.exit( 1 );
} // end catch
catch ( IllegalStateException stateException )
{
System.err.println( "Error reading from file." );
System.exit( 1 );
} // end catch
} // end method readRecords
// close file and terminate application
public void closeFile()
{
if ( input != null )
input.close(); // close file
} // end method closeFile
} // end class ReadTextFile
// Coding Exercise 2: ReadTextFileTest.java
// This program test class ReadTextFile.
public class ReadTextFileTest
{
public static void main( String args[] )
{
ReadTextFile application = new ReadTextFile();
application.openFile();
application.readRecords();
application.closeFile();
} // end main
} // end class ReadTextFileTest
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Lab sheet 5
Section: _
CPCS 203
Student Name: _____________________________
Enter the name of the file containing the student records:
students.txt
Student ID
1
2
3
First Name
Suzy
Jessica
Paul
Class average is: 87.60
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Last Name
Green
Purple
Orange
Grade
88.60
98.30
75.90
Lab sheet 5
Section: _
CPCS 203
Student Name: _____________________________
Lab sheet 5
Section: _
Postlab Activities
Name:
Programming Challenges
The Programming Challenges are more involved than the Coding Exercises and may require a significant amount
of time to complete. Write a Java program for each of the problems in this section. The answers to these problems
are available at www.pearsonhighered.com/deitel. Pseudocode, hints or sample outputs are
provided for each problem to aid you in your programming.
5. (Telephone-Number Word Generator) Standard telephone keypads contain the digits zero through nine. The
numbers two through nine each have three letters associated with them. (See Fig. L 5.3.) Many people find it
difficult to memorize phone numbers, so they use the correspondence between digits and letters to develop
seven-letter words that correspond to their phone numbers. For example, a person whose telephone number
is 686-2377 might use the correspondence indicated in Fig. L 5.3 to develop the seven-letter word “NUMBERS.” Each seven-letter word corresponds to exactly one seven-digit telephone number. The restaurant
wishing to increase its takeout business could surely do so with the number 825-3688 (i.e., “TAKEOUT”).
Each seven-letter phone number corresponds to many separate seven-letter words. Unfortunately, most
of these words represent unrecognizable juxtapositions of letters. It is possible, however, that the owner of a
barbershop would be pleased to know that the shop’s telephone number, 424-7288, corresponds to “HAIRCUT.” The owner of a liquor store would, no doubt, be delighted to find that the store’s number, 2337226, corresponds to “BEERCAN.” A veterinarian with the phone number 738-2273 would be pleased to
know that the number corresponds to the letters “PETCARE.” An automotive dealership would be pleased
to know that the dealership number, 639-2277, corresponds to “NEWCARS.”
Write a program that, given a seven-digit number, uses a Formatter object to write to a file every possible seven-letter word combination corresponding to that number. There are 2187 (37) such combinations. Avoid phone numbers with the digits 0 and 1.
Digit
Letters
2
A B C
3
D E F
4
G H I
5
J K L
6
M N O
7
P R S
8
T U V
9
W X Y
Fig. L 5.3 | Telephone keypad digits and letters.
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CPCS 203
Student Name: _____________________________
Lab sheet 5
Section: _
Solution
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// Programming Challenge 1 Solution: Phone.java
// Note: phone number must be input in the form #######.
// Only the digits 2 through 9 are recognized.
import java.io.File;
import java.io.FileNotFoundException;
import java.util.Formatter;
import java.util.FormatterClosedException;
import java.util.IllegalFormatException;
public class Phone
{
private int phoneNumber[];
// output letter combinations to file
public void calculate( int phoneNumber )
{
String letters[][] = { { " ", " ", " " },
{ " ", " ", " " }, { "A", "B", "C" }, { "D", "E", "F" },
{ "G", "H", "I" }, { "J", "K", "L" }, { "M", "N", "O" },
{ "P", "R", "S" }, { "T", "U", "V" }, { "W", "X", "Y" } };
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int digits[] = new int[ 7 ];
for ( int i = 6; i >= 0; i-- )
{
digits[ i ] = ( int )( phoneNumber % 10 );
phoneNumber /= 10;
} // end for
Formatter output = null;
try
{
output = new Formatter( "phone.txt" );
} // end try
catch ( SecurityException securityException )
{
System.out.println(
"You do not have write access to this file." );
System.exit( 1 );
} // end catch
catch ( FileNotFoundException fileNotFoundException )
{
System.out.println( "Error creating file." );
System.exit( 1 );
} // end catch
System.out.println( "Please wait..." );
try
{
int
int
int
int
int
loop1; //
loop2; //
loop3; //
loop4; //
loop5; //
loop
loop
loop
loop
loop
counter
counter
counter
counter
counter
for
for
for
for
for
first digit of phone number
second digit of phone number
third digit of phone number
fourth digit of phone number
fifth digit of phone number
CPCS 203
Student Name: _____________________________
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int loop6; // loop counter for sixth digit of phone number
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int loop7; // loop counter for seventh digit of phone number
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// output all possible combinations
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for ( loop1 = 0; loop1 <= 2; loop1++ )
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{
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for ( loop2 = 0; loop2 <= 2; loop2++ )
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{
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for ( loop3 = 0; loop3 <= 2; loop3++ )
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{
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for ( loop4 = 0; loop4 <= 2; loop4++ )
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{
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for ( loop5 = 0; loop5 <= 2; loop5++ )
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{
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for ( loop6 = 0; loop6 <= 2; loop6++ )
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{
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for ( loop7 = 0; loop7 <= 2; loop7++ )
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{
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output.format( "%s%s%s%s%s%s%s\n",
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letters[ digits[ 0 ] ][ loop1 ],
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letters[ digits[ 1 ] ][ loop2 ],
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letters[ digits[ 2 ] ][ loop3 ],
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letters[ digits[ 3 ] ][ loop4 ],
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letters[ digits[ 4 ] ][ loop5 ],
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letters[ digits[ 5 ] ][ loop6 ],
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letters[ digits[ 6 ] ][ loop7 ] );
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} // end for
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} // end for
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} // end for
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} // end for
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} // end for
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} // end for
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} // end for
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} // end try
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catch ( IllegalFormatException illegalFormatException )
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{
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System.out.println( "Error in format of output." );
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System.exit( 1 );
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} // end catch
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catch ( FormatterClosedException formatterClosedException )
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{
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System.out.println(
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"Error sending output; File has been closed." );
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System.exit( 1 );
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} // end catch
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System.out.println( "Done" );
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output.close(); // close output stream
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} // end method calculate
107 } // end class Phone
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Lab sheet 5
Section: _
CPCS 203
Student Name: _____________________________
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// Programming Challenge 1 Solution: PhoneTest.java
// Testing the Phone class.
import java.util.Scanner;
import java.util.NoSuchElementException;
public class PhoneTest
{
public static void main( String args[] )
{
Scanner scanner = new Scanner( System.in );
Phone application = new Phone();
System.out.print(
"Enter phone number (digits greater than 1 only): " );
try
{
application.calculate( scanner.nextInt() );
} // end try
catch ( NoSuchElementException elementException )
{
System.err.println( "Error inputting data." );
} // end catch
} // end main
} // end class PhoneTest
Enter phone number (digits greater than 1 only): 5556789
Please wait...
Done
A small portion of the contents of file phone.txt after PhoneTest.java executes.
JJJMPTW
JJJMPTX
JJJMPTY
JJJMPUW
JJJMPUX
JJJMPUY
...
47 | P a g e
Lab sheet 5
Section: _
CPCS 203
Student Name: _____________________________
Lab sheet 5
Section: _
Postlab Activities
Programming Challenges
6. (Student Poll) Figure 7.8 in Java How to Program contains an array of survey responses that is hard coded into
the program. Suppose we wish to process survey results that are stored in a file. This exercise requires two
separate programs. First, create an application that prompts the user for survey responses and outputs each
response to a file. Use a Formatter to create a file called numbers.txt. Each integer should be written using
method format. Then modify the program in Figure 7.8 to read the survey responses from numbers.txt.
The responses should be read from the file by using a Scanner. Method nextInt should be used to input
one integer at a time from the file. The program should continue to read responses until it reaches the end
of file. The results should be output to the text file "output.txt".
Solution
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// Programming Challenge 2 Solution: CreateResults.java
// Create poll results and output them to a file.
import java.io.FileNotFoundException;
import java.util.Formatter;
import java.util.FormatterClosedException;
import java.util.IllegalFormatException;
import java.util.NoSuchElementException;
import java.util.Scanner;
public class CreateResults
{
private int getValue()
{
int result = -1;
Scanner scanner = new Scanner( System.in );
// prompt the user for input
System.out.print(
"Enter integer result (1 - 10), -1 to quit: " );
try
{
result = scanner.nextInt();
} // end try
catch ( NoSuchElementException noSuchElementException )
{
System.err.println( "Error with input." );
System.exit( 1 );
} // end catch
return result;
} // end method getValue
private void outputData()
{
Formatter pollNumbers = null;
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try
{
// create the output stream
pollNumbers = new Formatter( "numbers.txt" );
int pollValue = getValue(); // get a number from the user
CPCS 203
Student Name: _____________________________
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// test for the sentinel value
while ( pollValue != -1 )
{
// if the number is valid
if ( pollValue > 0 && pollValue < 11 )
// write the value
pollNumbers.format( "%d\n", pollValue );
pollValue = getValue(); // get another value
} // end while
pollNumbers.close(); // close the file
} // end try
catch( SecurityException securityException )
{
System.err.println( "Error opening file." );
} // end catch
catch( FileNotFoundException fileNotFoundException )
{
System.err.println( "Output file cannot be found." );
} // end catch
catch( IllegalFormatException illegalFormatException )
{
System.err.println( "Error with the output's format." );
} // end catch
catch( FormatterClosedException formatterClosedException )
{
System.err.println( "File has been closed." );
} // end catch
finally
{
if ( pollNumbers != null )
pollNumbers.close();
} // end finally
} // end method outputData
public static void main( String args[] )
{
CreateResults application = new CreateResults();
application.outputData();
} // end main
} // end class CreateResults
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Lab sheet 5
Section: _
CPCS 203
Student Name: _____________________________
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// Programming Challenge 2 Solution: StudentPoll.java
// Read poll results from a file and output ratings.
import java.io.File;
import java.io.FileNotFoundException;
import java.util.Formatter;
import java.util.FormatterClosedException;
import java.util.IllegalFormatException;
import java.util.NoSuchElementException;
import java.util.Scanner;
public class StudentPoll
{
public void displayData()
{
int frequency[] = new int[ 11 ];
50 | P a g e
Formatter writer = null;
Scanner pollNumbers = null;
try
{
pollNumbers = new Scanner(
new File( "numbers.txt" ) );
writer = new Formatter( "output.txt" );
writer.format( "%-12s%-12s\n", "Rating", "Frequency" );
// for each answer, use that value as subscript to
// determine element to increment
while ( pollNumbers.hasNext() )
++frequency[ pollNumbers.nextInt() ];
// append frequencies to String output
for ( int rating = 1; rating < frequency.length; rating++ )
writer.format( "%-12d%-12d\n", rating, frequency[ rating ] );
} // end try
catch ( FileNotFoundException fileNotFoundException )
{
System.err.println( "Error: Files cannot be opened." );
} // end catch
catch ( FormatterClosedException formatterClosedException )
{
System.err.println( "Error: Output file is closed." );
} // end catch
catch ( SecurityException securityException )
{
System.err.println( "Error opening file for writing." );
} // end catch
catch ( IllegalFormatException illegalFormatException )
{
System.err.println( "Error writing data to file." );
} // end catch
catch ( NoSuchElementException noSuchElementException )
{
System.err.println( "Error reading from file." );
} // end catch
catch ( IllegalStateException illegalStateException )
{
System.err.println( "Error: Input file is closed." );
} // end catch
finally
{
if ( writer != null )
writer.close();
Lab sheet 5
Section: _
CPCS 203
Student Name: _____________________________
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if ( pollNumbers != null )
pollNumbers.close();
} // end finally
} // end displayData
} // end class StudentPoll
// Programming Challenge 2 Solution: StudentPollTest.java
// Testing the StudentPoll class.
public class StudentPollTest
{
public static void main( String args[] )
{
StudentPoll application = new StudentPoll();
application.displayData();
} // end main
} // end class StudentPollTest
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Lab sheet 5
Section: _