Download String

CPSC 233 - Introduction to
Computer Science for Computer
Science Majors II
Monir Zaman
(Md Moniruzzaman)
Tip: Error Messages
• Bug: A mistake in a program
– The process of eliminating bugs is called
debugging
• Syntax error: A grammatical mistake in a
program
– The compiler can detect these errors, and will
output an error message saying what it thinks the
error is, and where it thinks the error is
1-2
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reserved.
• Compute 1+2+...+5 and output the result:
int i=0,sum=0;
while(++i<5){
sum=sum+i;
//System.out.println(i);
}
System.out.println(sum);
• Compute 1+2+...+5 and output the result:
int i=0,sum=0;
while(i++<5){
sum=sum+i;
//System.out.println(i);
}
System.out.println(sum);
Tip: Error Messages
• Run-time error: An error that is not detected until a
program is run
– The compiler cannot detect these errors: an error
message is not generated after compilation, but after
execution
• Logic error: A mistake in the underlying algorithm
for a program
– The compiler cannot detect these errors, and no error
message is generated after compilation or execution, but
the program does not do what it is supposed to do
1-5
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reserved.
• Print all the elements of an array
int[] ar={23,45,67};
int i=0;
while(i<4){
System.out.println(ar[i]);
i++;
}
• Print all the elements of an array
int[] ar={23,45,67};
int i=0;
while(i<ar.length){
System.out.println(ar[i]);
i++;
}
int num=45;
if(num>20){
if(num<10){
num*=10;
}
}
Class String
• Store text
String name=“John”;
String name=null;
String name;
String
String name=“John”;
name.equals(“smith”)
Returns a boolean value: true/false
String name=“John”;
If( name.equals(“smith”) ) {
System.out.printf(“Names %s and %s are equal”, name, “smith”);
}
String
String name=“John”;
name.equalsIgnoreCase(“joHn”)
Returns a boolean value: true
Method definition
boolean equals (String)
boolean equalsIgnoreCase (String)
String toUpperCase()
String toLowerCase()
String toUpperCase()
String toLowerCase()
Example:
String a_b=“stat101”;
System.out.println(a_b.toUpperCase());
STAT101
Some Methods in the Class String (Part 3 of 8)
1-16
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reserved.
Some Methods in the Class String (Part 4 of 8)
1-17
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reserved.
Some Methods in the Class String (Part 5 of 8)
1-18
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reserved.
File Input
import java.util.Scanner;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
public class tryfileIO{
public static void main(String[] args){
//this is comment
try{
FileInputStream fis=new FileInputStream("/home/grads/mmoniruz/temp.txt");
Scanner fin=new Scanner(fis);
System.out.printf("%s%n",fin.nextLine());
}//end of try
catch(FileNotFoundException e){
System.out.println(“Error message "+e);
System.exit(0);
}//end of catch
}//end of main
}//end of class
File Input
import java.util.Scanner;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
public class tryfileIO{
public static void main(String[] args){
try{
FileInputStream fis=new FileInputStream("/home/grads/mmoniruz/temp.txt");
Scanner fin=new Scanner(fis);
while(fin.hasNextLine()){
System.out.printf("%s%n",fin.nextLine());
}
}//end of try
catch(FileNotFoundException e){
System.out.println(“Error message "+e);
System.exit(0);
}//end of catch
}//end of main
}//end of class
Some Methods in the Class String (Part 6 of 8)
1-21
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reserved.
Some Methods in the Class String (Part 7 of 8)
1-22
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reserved.
Some Methods in the Class String (Part 7 of 8)
String name=“JOHN”;
name.compareTo(“john”)
returns a negative number
1-23
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Addison-Wesley. All rights
reserved.
Some Methods in the Class String (Part 8 of 8)
1-24
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Addison-Wesley. All rights
reserved.
Exercise
• Write a program that starts with a line of text and then
outputs that line with the first occurrence of “hate”
changed to “love”. A sample output of the program:
The line of text to be changed is:
I hate strong wind.
I have rephrased that line to read:
I love strong wind.
Use a defined constant to store the line of text. You can have
the word “hate” more than once in the line but change only
its first occurrence.
Exercise II
• Create a text file containing the text “I hate strong wind.”
• Write a program that reads the text from the file and
changes the first occurrence of “hate” to “love”. A sample
output of the program:
The line of text to be changed is:
I hate strong wind.
I have rephrased that line to read:
I love strong wind.
You can have the word “hate” more than once in the line but
change only its first occurrence.