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Java Programming
Week 1: Java Fundamental Revision
(Text book: ch1, ch2, ch3, ch4)
Course Introduction
Course Coordinator
Lily D. Li
Course Resources
Website (contains course profile, slides, study
guide including tuts tasks and news)
http://webfuse.cqu.edu.au/Courses/2008/T2/COIT11134/
Text book
Big Java, Cay Horstmann, 3nd Edition
COIT11134-Java Programming
2
Delivery Model
External Students
Textbook, Slides, Study Guide, online forum and
mailing lists
Internal Students
Above plus
2 hours lecture per week
2 hours lab per week
COIT11134-Java Programming
3
Course Structure
1.
2.
3.
4.
5.
6.
Java Revision (Java data types, object,
class, JDK)
Revision (decision and iteration), instance
methods and static method
Interface and Polymorphism
Inheritance
Graphic User Interface
Array and ArrayList
COIT11134-Java Programming
4
Course Structure cont.
7.
8.
9.
10.
11.
12.
Sorting and Searching
Sorting and Searching
Input/Ourput, Exception handling, Files
and Streams
Object-Oriented Design
Object-Oriented Design
Final revision
COIT11134-Java Programming
5
Assessment
Assignment 1:
GUI, Event Handling, Exception Handling
(Week 6,
15%)
Assignment 2:
Object Sorting
(Week 11, 20%)
Final exam:
All topics covered, 65%
Pass criteria:
50% plus overall AND 50% final exam
COIT11134-Java Programming
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Week 1: Learning Objectives
Familiarise yourself with editing, compile and run
Java programs with TextPad if you are not
confident
Review topics in Chapter 1, Chapter 2, Chapter
3, Chapter 4 of the text book.
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The Java Programming Language
Principles of Java
Simple to learn (API)
Safe to use
Platform-Independent (written once, run
everywhere) (JVM)
Rich Library Resources
Designed for the Internet
Apply to smallest embedded systems and largest
enterprise-wide application
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Three types of Java programs
Java Applications
Run stand alone, any size, run from command line
or a GUI
Java Applets
Run in Java-enabled web browsers, launched from
HTML files
Java Servlets
Similar to Applets, generate contents for web page
(HTML doc), run in Java-enabled web server
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Java Examples
A Java Application Example
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Java Examples
A Java Applet Example
http://java.sun.com/applets/jdk/1.4/demo/apple
ts/SortDemo/example1.html
A Java Servlet Example
http://forum.java.sun.com/forum.jspa?forumID
=31
(In many J2EE application, online forum,
registration, normally need to operate on
databases)
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Questions
How long would it take to learn the entire
Java Library?
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Questions
How long would it take to learn the entire
Java Library?
No one person can learn the entire library, it is too
large.
It is still growing
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The J2SE SDK
“The Java 2 Standard Edition, Standard Development Kit
(J2SE SDK) provides a complete environment for
application development on desktops and servers” (Sun,
2005).
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The J2SE SDK Cont…
For this subject you will need
The recent version of the J2SE SDK, such as
J2SE SDK Java 6 or later
The previous Java 5 is also good enough for the
course
TextPad – a Text editor with Java compiling, execution built-in
You should have above software and environment
configured in the prerequisites course, if not, please do it in
week 1
If you are using university labs for your study, the software
is ready on campus labs.
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Development Environment
Java programs can be developed, compiled
and executed in either
A Console Window (DOS Command Window)
or
An Integrated Development Environment (IDE) like Eclipse
or
Some development tools with Java built-in like TextPad
For this course, any environments are allowed to be
used, TextPad is preferred
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A Simple Program Structure
public class HelloWorld
{
public static void main (String[ ] args)
{
System.out.println(“Hello, World!”);
}
}
main method is an entry of an Java application. It must be declared
as: public static void main (String[ ] args)
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The Compilation Process
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Types and Variables
Every value has a type
Variables
Store values
Can be used in place of the objects they store
Variable declaration and initialization
String greeting = "Hello, World!";
int luckyNumber = 13;
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Identifiers
Identifier: name of a variable, method, or
class
Rules for identifiers in Java:
Can be made up of letters, digits, and the underscore (_)
character
Cannot start with a digit
Cannot use other symbols such as ? or %
Spaces are not permitted inside identifiers
You cannot use reserved words
They are case sensitive
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Continued… 20
Identifiers
By convention, variable names start with a
lowercase letter
By convention, class names start with an
uppercase letter
By convention, method names start with a
lowercase letter
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Objects and Classes
Object: entity that you can manipulate in your
programs (by calling methods)
Each object belongs to a class. For example,
System.out (will return an object type)
belongs to the class PrintStream
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Methods
Method: Sequence of instructions that accesses the
data of an object
Methods are public interface: Specifies what you
can do with the objects of a class
You manipulate objects by calling its methods
Class: Set of objects with the same behavior
Class determines legal methods
String greeting = "Hello";
greeting.println() // Error
greeting.length() // OK
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A Representation of Two String Objects
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String Methods
length(): counts the number of characters
in a string
String greeting = "Hello, World!";
int n = greeting.length(); // sets n to 13
toUpperCase(): creates another String
object that contains the characters of the
original string, with lowercase letters converted
to uppercase
String river = "Mississippi";
String bigRiver = river.toUpperCase();
// sets bigRiver to "MISSISSIPPI"
COIT11134-Java Programming
Continued…
25
String Methods
When applying a method to an object, make
sure method is defined in the appropriate
class
System.out.length(); // This method call is an error
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Return Values
Return value: A result that the method has
computed for use by the code that called it
int n = greeting.length(); // return value stored in n
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Continued…
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Passing Return Values
You can also use the return value as a
parameter of another method:
System.out.println(greeting.length());
Not all methods return values. Example:
println
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Continued…
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Method Definitions
Method definition specifies types of explicit
parameters and return value
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Continued…
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Method Definitions
Example: Class String defines
public int length()
// return type: int
// no explicit parameter
public String replace(String target, String replacement)
// return type: String;
// two explicit parameters of type String
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Method Definitions
If method returns no value, the return type is
declared as void
public void println(String output) // in class PrintStream
A method name is overloaded if a class has
more than one method with the same name
(but different parameter types)
public void println(String output)
public void println(int output)
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Rectangular Shapes and Rectangle
Objects
Objects of type Rectangle describe
rectangular shapes
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Rectangular Shapes and
Rectangle Objects
A Rectangle object isn't a rectangular
shape–it is an object that contains a set of
numbers that describe the rectangle
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Constructing Objects
new Rectangle(5, 10, 20, 30)
Detail:
1. The new operator makes a Rectangle object
It uses the parameters (in this case, 5, 10, 20, and 30)
to initialize the data of the object
3. It returns the object
Usually the output of the new operator is stored in a variable
2.
Rectangle box = new Rectangle(5, 10, 20, 30);
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Constructing Objects
The process of creating a new object is called
construction
The four values 5, 10, 20, and 30 are called
the construction parameters
Some classes let you construct objects in
multiple ways
new Rectangle()
// constructs a rectangle with its top-left corner
// at the origin (0, 0), width 0, and height 0
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Object Construction
new ClassName(parameters)
Example:
new Rectangle(5, 10, 20, 30)
new Rectangle()
Purpose:
To construct a new object, initialize it with the construction parameters, and
return a reference to the constructed object
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Accessor and Mutator Methods
Accessor method: does not change the
state of the objects (e.g. get methods)
double width = box.getWidth();
Mutator method: changes the state
of the objects (e.g. set methods)
box.translate(15, 25);
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Importing Packages
Java classes are grouped into packages
Import library classes by specifying the
package and class name:
import java.awt.Rectangle;
You don't need to import classes in the
java.lang package such as String and
System
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The API Documentation
API doc: Application Programming Interface
docs
Lists classes and methods in the Java library
http://java.sun.com/javase/6/docs/api/
You will need to check Java API documents
very frequently in the future
It still grows
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Object References
Describe the location of objects
The new operator returns a reference to a new
object
Rectangle box = new Rectangle();
Multiple object variables can refer to the same
object
Rectangle box = new Rectangle(5, 10, 20, 30);
Rectangle box2 = box;
box2.translate(15, 25);
COIT11134-Java Programming
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Continued…
Object Variables and Number
Variables
An Object Variable containing an Object Reference
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Object Variables and Number
Variables
A Number Variable Stores a Number
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Copying Numbers
int luckyNumber = 13;
int luckyNumber2 = luckyNumber;
luckyNumber2 = 12;
Copying Numbers
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Copying Object References
Rectangle box = new Rectangle(5, 10, 20, 30);
Rectangle box2 = box;
box2.translate(15, 25);
Copying Object References
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Implement Classes
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Designing the Public Interface
of a Class
Behavior of bank account (abstraction):
deposit money
withdraw money
get balance
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Designing the Public Interface of a
Class: Methods
Methods of BankAccount class:
deposit
withdraw
getBalance
We want to support method calls such as the
following:
harrysChecking.deposit(2000);
harrysChecking.withdraw(500);
System.out.println(harrysChecking.getBalance());
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Designing the Public Interface of a
Class: Method Definition
access specifier (such as public)
return type (such as String or void)
method name (such as deposit)
list of parameters (double amount for
deposit)
method body in { }
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Continued…
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Designing the Public Interface of a
Class: Method Definition
Examples
public void deposit(double amount) { . . . }
public void withdraw(double amount) { . . . }
public double getBalance() { . . . }
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Constructor Definition
A constructor initializes the instance variables
Constructor name = class name
public BankAccount()
{
// body--filled in later
}
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Continued…
50
Constructor Definition
Constructor body is executed when new
object is created
Statements in constructor body will set the
internal data of the object that is being
constructed
All constructors of a class have the same
name
Compiler can tell constructors apart because
they take different parameters
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Constructor Definition
accessSpecifier ClassName(parameterType parameterName, . . .)
{
constructor body
}
Example:
public BankAccount(double initialBalance)
{
. . .
}
Purpose:
To define the behavior of a constructor
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Class Definition
accessSpecifier class ClassName
{
constructors
methods
fields
}
Example:
public class BankAccount
{
public BankAccount(double initialBalance) { . . . }
public void deposit(double amount) { . . . }
. . .
}
Purpose:
To define a class, its public interface, and its implementation details
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Question
How can you use the methods of the public
interface to empty the harrysChecking bank
account?
The public interface as following
public void deposit(double amount) { . . . }
public void withdraw(double amount) { . . . }
public double getBalance() { . . . }
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Answers
harrysChecking.withdraw(harrysChecking.getBalance())
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Instance Fields
An object stores its data in instance fields
Field: a technical term for a storage location
inside a block of memory
Instance of a class: an object of the class
The class declaration specifies the instance
fields:
public class BankAccount
{
. . .
private double balance;
}
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Instance Fields
An instance field declaration consists of the
following parts:
access specifier (such as private)
type of variable (such as double)
name of variable (such as balance)
Each object of a class has its own set of
instance fields
You should declare all instance fields as
private
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Instance Fields
Instance Fields
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Instance Field Declaration
accessSpecifier class ClassName
{
. . .
accessSpecifier fieldType fieldName;
. . .
}
Example:
public class BankAccount
{
. . .
private double balance;
. . .
}
Purpose:
To define a field that is present in every object of a class
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Accessing Instance Fields
The deposit method of the BankAccount
class can access the private instance field:
public void deposit(double amount)
{
double newBalance = balance + amount;
balance = newBalance;
}
Continued…
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Implementing Constructors
Constructors contain instructions to initialize
the instance fields of an object
public BankAccount()
{
balance = 0;
}
public BankAccount(double initialBalance)
{
balance = initialBalance;
}
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Implementing Methods
Some methods do not return a value
public void withdraw(double amount)
{
double newBalance = balance - amount;
balance = newBalance;
}
Some methods return an output value
public double getBalance()
{
return balance;
}
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File BankAccount.java
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/**
A bank account has a balance that can be changed by
deposits and withdrawals.
*/
public class BankAccount
{
/**
Constructs a bank account with a zero balance.
*/
public BankAccount()
{
balance = 0;
}
/**
Constructs a bank account with a given balance.
@param initialBalance the initial balance
*/
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Continued… 63
File BankAccount.java
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public BankAccount(double initialBalance)
{
balance = initialBalance;
}
/**
Deposits money into the bank account.
@param amount the amount to deposit
*/
public void deposit(double amount)
{
double newBalance = balance + amount;
balance = newBalance;
}
/**
Withdraws money from the bank account.
@param amount the amount to withdraw
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Continued… 64
File BankAccount.java
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*/
public void withdraw(double amount)
{
double newBalance = balance - amount;
balance = newBalance;
}
/**
Gets the current balance of the bank account.
@return the current balance
*/
public double getBalance()
{
return balance;
}
private double balance;
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Testing a Class
Test class: a class with a main method that
contains statements to test another class.
Typically carries out the following steps:
1.
2.
3.
Construct one or more objects of the class that
is being tested
Invoke one or more methods
Print out one or more results
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Continued… 66
File BankAccountTester.java
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/**
A class to test the BankAccount class.
*/
public class BankAccountTeste
{
/**
Tests the methods of the BankAccount class.
@param args not used
*/
public static void main(String[] args)
{
BankAccount harrysChecking = new BankAccount();
harrysChecking.deposit(2000);
harrysChecking.withdraw(500);
System.out.println(harrysChecking.getBalance());
}
}
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Fundamental Data Types
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Categories of Variables
Categories of variables
Instance fields (balance in BankAccount)
Local variables (newBalance in deposit
method)
Parameter variables (amount in deposit
method)
An instance field belongs to an object
The fields stay alive until no method uses the
object any longer
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Categories of Variables
In Java, the garbage collector periodically
reclaims objects when they are no longer
used
Local and parameter variables belong to a
method
Instance fields are initialized to a default
value, but you must initialize local variables
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Primitive Types
Type
Description
Size
int
The integer type, with range
–2,147,483,648 to 2,147,483,647
4 bytes
byte
The type describing a single byte, with
range
–128 to 127
1 byte
short
The short integer type, with range
–32768 to 32767
2 bytes
long
The long integer type, with range –
9,223,372,036,854,775,808 to
–9,223,372,036,854,775,807
8 bytes
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Continued…
Primitive Types
Type
Description
Size
double
The double-precision floating-point type,
with a range of about ±10308 and about
15 significant decimal digits
8 bytes
float
The single-precision floating-point type,
with a range of about ±1038 and about 7
significant decimal digits
4 bytes
char
The character type, representing code
2 bytes
units in the Unicode encoding scheme
The type with the two truth values false 1 byte
and true
boolean
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Number Types: Conversion
Type Casting: This is a method which is
commonly used for type conversion.
double balance = 23.45;
int dollars = (int) balance; // OK
Cast discards fractional portion.
Continued…
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Number Types: Conversion
Math.round: Can be used to convert a floating point
type to an integer type:
// if balance is 130.75, then rounded is set to 131
float balance = 130.75;
long rounded = Math.round(balance);
Conversions can be made larger types using standard
assignments:
int dollars = 15;
float price = dollars; //OK
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Constants: final
Declaring <final> before type is Java’s standard for
creating constants.
final int MINUTES_IN_HOUR = 60;
Once its value has been set, it cannot be changed
Convention: use all-uppercase characters for constant
names and separate with underscore.
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Constants: static final
Use <static final>, if constant values are needed in
several classes.
Give static final constants public access to enable
other classes to use them.
public class Math
{
. . .
public static final double E = 2.718281828;
public static final double PI = 3.14159265;
}
//this uses the constant to perform a calculation
double circumference = Math.PI * diameter;
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Calling Static Methods
A static method does not operate on an object:
double x = 4;
double root = x.sqrt(); // Error
double root = Math.sqrt(x); //OK
Static methods are defined inside classes
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Some Math Methods
Math.sqrt(x)
square root
Math.pow(x, y)
power xy
Math.exp(x)
ex
Math.log(x)
natural log
Math.sin(x), Math.cos(x), sine, cosine, tangent (x in
Math.tan(x)
radian)
Math.round(x)
closest integer to x
Math.min(x, y),
Math.max(x, y)
minimum, maximum
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Strings: Concatenation
Use the <+> operator to add to a string:
String name = "Dave";
String message = "Hello, " + name;
// message is now "Hello, Dave"
If one of the arguments of the <+> operator is a string, the
other is converted to a string.
String name = “Dave is: ";
int age = 27;
String person = name + age; // dave is “Dave is: 27”
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Conversion: Strings and
Numbers
Convert from string to number:
int n = Integer.parseInt(str);
double x = Double.parseDouble(str);
Convert from number to string:
String str = "" + n;
str = Integer.toString(n);
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Substrings
String greeting = "Hello, World!";
String sub = greeting.substring(0, 5); // sub is "Hello"
Supply start and end position.
(note: the start position you want, the end position you don’t
want)
First position is at 0
Continued…
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Reading Input
Scanner class was added to read
keyboard input in a convenient manner
Scanner in = new Scanner(System.in);
System.out.print("Enter quantity: ");
int quantity = in.nextInt();
nextDouble reads a double
nextLine reads a line (until user hits Enter)
next reads a word (until any white space)
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File InputTester.java
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import java.util.Scanner;
/**
This class tests console input.
*/
public class InputTester
{
public static void main(String[] args)
{
Scanner in = new Scanner(System.in);
CashRegister register = new CashRegister();
System.out.print("Enter price: ");
double price = in.nextDouble();
register.recordPurchase(price);
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Continued…
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File InputTester.java
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System.out.print("Enter dollars: ");
int dollars = in.nextInt();
System.out.print("Enter quarters: ");
int quarters = in.nextInt();
System.out.print("Enter dimes: ");
int dimes = in.nextInt();
System.out.print("Enter nickels: ");
int nickels = in.nextInt();
System.out.print("Enter pennies: ");
int pennies = in.nextInt();
register.enterPayment(dollars, quarters, dimes,
nickels, pennies);
System.out.print("Your change is ");
System.out.println(register.giveChange());
}
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Continued…
File InputTester.java
Output
Enter price: 7.55
Enter dollars: 10
Enter quarters: 2
Enter dimes: 1
Enter nickels: 0
Enter pennies: 0
Your change is 3.05
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Reading Input from a Dialog
Box
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Reading Input From a Dialog
Box
String input = JOptionPane.showInputDialog(prompt)
Convert strings to numbers if necessary:
int count = Integer.parseInt(input);
Conversion throws an exception if user
doesn't supply a number
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References
Sun Microsystems “Java Downloads”.
http://java.sun.com/j2se/index.jsp (Sun)
Horstmann C. 2007, Big Java, Wiley & Sons
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