Java Getting Started

1
Java Getting Started

• Ching-Hong Tsai
• CSIE, National Chiao-Tung University
• chtsai_at_csie.nctu.edu.tw

2
Introduction

• The Java Phenomenon
• The Hello World Applet
• The Hello World Application

3
The Java Phenomenon

• Origins of Java
• Features of Java
• Java Applet and Application

4
Origins of Java

• 1991 Sun Microsystems
• James Gosling
• Create programs to control consumer electronics
• C is not suitable
• From Oak to Java
• Early Project - Green Team
• Star Seven (7)
• In 2Q of 1995, Sun Microsystems officially
  announced Java and HotJava

5
What is Java?

• Java is a general-purpose, high-level programming
  language.
• The features of Java
• Java program is both compiled and interpreted.
• Write once, run anywhere

6
Features of Java

• Simple
• Architecture-neutral
• Object-Oriented
• Distributed
• Compiled
• Interpreted
• Statically Typed
• Multi-Threaded
• Garbage Collected

• Portable
• High-Performance
• Robust
• Secure
• Extensible
• Well-Understood

7
How Will Java Change My Life

• Get started quickly
• Write less code
• Write better code
• Develop programs faster
• Avoid platform dependencies with 100 pure Java
• Write once, run anywhere
• Distribute software more easily

8
Java Applets and Applications

• Applet
• Run under a Java-Enabled Browser
• Stand-alone Applications
• Just like any programming languages

9
Java Developer's Kit (I)

• Java's programming environment
• compiler
• interpreter
• debugger
• disassembler
• profiler
• more...

10
Java Developer's Kit
Java Interpreter
Java Compiler
Compile
Run
Java Source
Java Bytecode
ltfilegt.java
ltfilegt.class
Java Disassembler
11
Java Is Compiled and Interpreted
12
Prepare and Execute Java
Internet
Verification
Your computer
Java ByteCode
Execution
Restricted Env.
13
Write Once, Run Anywhere
14
The Hello World Application

• Comments in Java Code
• Defining a Class
• The main() Method
• Using Classes and Objects

15
Create a Java Source File

• HelloWorldApp/ The HelloWorldApp class
  implements an application that simply displays
  "Hello World!" to the standardoutput. /public
  class HelloWorldApp public static void
  main(String args) System.out.println("Hello
  World!") //Display the string.

16
Compile and Run

• Compile
• javac HelloWorldApp.java
• Run
• java HelloWorldApp

17
Comments in Java Code

• / Text /
• / Documentation / (Used by javadoc tool)
• //Text (Ignore everything from // to the end of
  the line)

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Defining a Class

• Define a class in Java
• class name .
• In Java, every method (function) and variable
  exists within a class or an object.
• Java does not support global functions or
  variables.
• The Hello World application has no variables
  and has a single method named main.

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The main Method

• Each Java application must contain a main method
  whose signature looks like this
• public static void main(String args)
• Modifier in the main method
• public The main method can be called by any
  object.
• static The main method is a class method.
• void The main method does not return any value.

20
Using Classes and Objects

• A class method or class variable is associated
  with a particular class.
• ltclass namegt.ltmethod/variable namegt
• An instance method or instance variable is
  associated with a particular object (an instance
  of a class)
• ltinstance namegt.ltmethod/variable namegt

21
The Hello World Applet

• Importing Classes and Packages
• Defining an Applet Subclass
• Implementing Applet Methods
• Running an Applet

22
Create a Java Source File

• HelloWorld.javaimport java.applet.Appletimport
  java.awt.Graphicspublic class HelloWorld
  extends Applet public void paint(Graphics g)
  g.drawString(Hello World!, 50, 25)

23
Compile the Source File

• javac HelloWorld.java
• One file named HelloWorld.class is created if the
  compilation is succeeds.

24
Create an HTML File that Includes the Applet

• Hello.htmlltHTMLgtltHEADgtltTITLEgt A Simple Program
  lt/TITLEgtlt/HEADgtltBODYgt Here is the output of my
  programltAPPLET CODE"HelloWorld.class"
  WIDTH150 HEIGHT60gtlt/APPLETgtlt/BODYgtlt/HTMLgt

25
Import Classes and Packages

• Packages are used to group classes, similar to
  the way libraries are used to group C functions.
• Importing classes lets a program refer to them
  later without any prefixes.
• Within a package, all classes can refer to each
  other without prefixes.
• java.applet and java.awt packages are part of the
  core Java API
• You can also import entire packages

26
Defining An Applet Subclass

• The extends keyword indicates the HelloWorld is a
  subclass of the class whose name follows Applet.
• The Applet class has the ability to respond to
  browser requests and others.
• An applet isnt restricted to defining just one
  class.

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Implementing Applet Methods

• Every applet must implement one or more of the
  init, start, and paint methods.
• An applet can implement two more methods stop
  and destroy.
• An applet does not need to implement a main
  method, like a Java Application.

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Running An Applet

• Use ltAPPLETgtlt/APPLETgt in a HTML file to refer to
  an Java applet.
• ltAPPLET CODEJava_Class WIDTHltNgt HEIGHTltMgt gt

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Without Import

• public class HelloWorld extends
  java.applet.Applet public void
  paint(java.awt.Graphics g)
  g.drawString(Hello World!, 50, 25)

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Import Entire Packages

• HelloWorld.javaimport java.applet. import
  java.awt. public class HelloWorld extends
  Applet public void paint(Graphics g)
  g.drawString(Hello World!, 50, 25)

31
Object-Oriented Programming Concepts

• What are Objects?
• What are Classes?
• What are Messages?
• What is Inheritance?

32
What Are Objects?

• Definition An object is a software bundle of
  variables and related methods.
• These real-world objects characteristics they
  all have state and they all have behavior.
• A software object
• maintains its state in variables
• implements its behavior with methods

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What Are Objects?

• For example
• dogs have state (name, color, breed, hungry)
• dogs have behavior (barking, fetching, and
  slobbering on your newly cleaned slacks)
• Bicycles have state (current gear, current pedal
  cadence, two wheels, number of gears)
• Bicycles have behavior (braking, accelerating,
  slowing down, changing gears)

34
What Are Objects?

• You can represent real-world objects using
  software objects
• You might want to represent real-world dogs as
  software objects in an animation program
• A real-world bicycle as a software object within
  an electronic exercise bike

35
Visual Representation of A Software Object
Variable
Method
36
Software Bicycle

• Instance Variables and Instance Method

37
Encapsulation

• Packaging an object's variables within the
  protective custody of its methods
• Methods surround and hide the object's center
  from other objects.
• Benefit of encapsulation
• Modularity
• Information hiding

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Encapsulation

• Change gears on your bicycle, you don't need to
  know how the gear mechanism works, you just need
  to know which lever to move
• In many languages, including Java, an object can
  choose to expose its variables to other objects
  allowing those other objects to inspect and even
  modify the variables.

39
What Are Classes?

• Definition A class is a blueprint or prototype
  that defines the variables and methods common to
  all objects of a certain kind
• An object is an instance of a certain class.
• After you've created the class, you must
  instantiate it (create an instance of it) before
  you can use it
• The benefit of Classes Reusability

40
What Are Classes?

• Class variables and class methods
• You can access class variables and methods from
  an instance of the class or directly from a
  class.
• All instances share this variable. If one object
  changes the variable, it changes for all other
  objects of that type.

41
Visual Representation of A Software Class
42
What Are Messages?

• Software objects interact and communicate with
  each other by sending messages to each other.

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Message Example
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More on Messages

• Components of a Message
• The object to whom the message is addressed (Your
  Bicycle)
• The name of the method to perform(changeGears)
• Any parameters needed by the method (low gear)
• Your Bicycle.changeGears(low gear)

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More on Messages

• The Benefits of Messages
• Messages passing supports all possible
  interactions between objects (aside from direct
  variable access)
• Objects dont need to be in the same process or
  even on the same machine to send and receive
  messages.

46
What is Inheritance?

• Inheritance allows classes to be defined in terms
  of other classes
• superclass and subclass
• Each subclass inherits variables and methods from
  its superclass.
• Subclasses can add variables and methods to the
  ones they inherit from the superclass.

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What is Inheritance?

• Subclasses can also override inherited method and
  provide specialized implementations for those
  methods.
• Inheritance or class hierarchy
• The inheritance tree, or class hierarchy, can be
  as deep as needed.
• Methods and variables are inherited down through
  the levels

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Benefits of Inheritance

• Programmers can reuse the code in the superclass
  many times.
• Programmers can implement superclasses called
  abstract classes
• Abstract class defines generic behaviors
• Define and may partially implement the behavior
  but much of the class is undefined and
  unimplemented. Other programmers fill in the
  details with specialized subclasses.

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Inheritance Example
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Java Programming Language Overview

• General Features of Java Programming Language
• Variables and Data Types
• Operators
• Expressions
• Control Flow Statements
• Introduction to Classes and Object
• Introduction to Java Classes
• The Life Cycle of an Object

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General Features of Java Programming Language

• Variables and Data Types
• Operators
• Expressions
• Control Flow Statements
• Array

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The Count Class

• import java.io.public class Count public
  static void countChars(Reader in)
  throws IOException int count 0
  while (in.read() ! -1) count
  System.out.println("Counted " count "
  chars.")

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Running the countChars

• import java.io.public class Count // ...
  countChars method omitted ...public static void
  main(String args) throws Exceptionif
  (args.length gt 1) countChars(new
  FileReader(args0))else System.err.println("U
  sage Count filename")

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Variables and Data Types

• Variable Declaration
• Data Type
• Variable

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Variable Declaration

• Variable Declaration
• Type of the variable
• Name of the variable
• The location of the variable declaration
  determines its scope.

56
Data Type

• Java is static-typed All variables must have a
  type and have to be declared before use.
• A variables' data type determines its value and
  operation
• Two categories of data types in Java
• primitive data type byte, short, int, long,
  float....
• reference data type class, interface, array

57
Primitive Data Types

• byte 8-bit
• short 16-bit
• int 32-bit
• long 64-bit
• float 32-bit floating point
• double 64-bit floating point
• char 16-bit Unicode
• boolean true/false

58
Variable Names

• Java refers to a variable's value by its name.
• General Rule
• Legal Java identifier
• Not a keyword or a boolean literal
• Not the same name as another in the same scope
• Convention
• Variable names begin with a lowercase letter
• Class names begin with an uppercase letter

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Variable Scope

• The location of the variable declaration within
  your program establishes its scope
• Variable Scope
• Member variable
• Local variable
• Method parameter
• Exception-handler parameter

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Variable Scope
61
Variable Initialization

• Local variables and member variables
• can be initialized with an assignment statement
  when they're declared.
• data type of the assignment statement must match.
• Method parameters and exception-handler
  parameters
• cannot be initialized in the same way as
  local/member variables
• The value for a parameter is set by the caller.

62
Final Variables

• The value of a final variable cannot change after
  it has been initialized.
• You can view final variables as constants.
• Declaration and Initialization
• final int aFinalVar 0
• final int blankfinal . . .
  blankfinal 0

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Literals (I)

• To represent the primitive types
• Integer
• Decimal Value
• Hexadecimal Value 0x... (0x1f 31)
• Octal Value 0... (07662)
• Floating Point
• 3.1415
• 6.1D2 (64-bit Double Default)
• 3.4F3 (32-bit Float)

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Literals (II)

• Characters
• ' ..... '
• '\t', '\n' (Escape Sequence)
• Strings
• "......."
• String Class (Not primitive data type)

65
Operators

• Operators perform some function on operands.
• An operator also returns a value.

66
Operators (I)

• Arithmetic Operators
• Binary , -, , /,
• Unary , -, op, op, op--, --op
• Relational Operators
• gt, gt, lt, lt, , ! (return true and false)
• Conditional Operators
• (AND), (OR), !(NOT), (AND), (OR)
• expression ? op1 op2

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Operators (II)

• Bitwise Operators
• gtgt, ltlt, gtgtgt, , ,,
• Assignment Operators
• -, , /, , , !, , ltlt, gtgt, gtgtgt

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Expressions

• Perform the work of a Java Program
• Perform the computation
• Return the result of the computation

69
Expression

• An expression is a series of variables,
  operators, and method calls that evaluates to a
  single value.
• Precedence
• Precedence Table
• Use (.....)
• Equal precedence
• Assignment Right to Left (a b c)
• Other Binary Operators Left to Right

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Expression

• postfix operators . (params) expr
  expr--
• unary operators expr --expr expr
  -expr !
• creation or cast new (type)expr
• multiplicative /
• additive -
• shift ltlt gtgt gtgtgt
• relational lt gt lt gt instanceof
• equality !
• bitwise AND
• bitwise exclusive OR
• bitwise inclusive OR
• logical AND
• logical OR
• conditional ?
• assignment - /
  ltlt gtgt gtgtgt

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Control Flow Statement

• If Statements
• Loops
• Switch
• Break and Continue

72
If Statements

• if (boolean) / ... / else if (boolean) /
  ... / else / ... /
• The expression in the test must return a boolean
  value
• Zero('') can't be used to mean false, or
  non-zero("...") to mean true

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Loops

• while (boolean expression) / ... /
• do / ... / while (boolean expression)
• for (expression booleanExpression expression)
  / ... /

74
Switch

• switch (expression) case Constant1/ ...
  /breakcase Constant2/ ...
  /break....default/ ... /break

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Break and Continue

• Same meaning as in C
• A optional label can be used. Break/Continue with
  the statement that is declared.
• outer // labelfor (int j0 j lt 10 j)
  / Continue goes to here / for (int i0 i lt
  20 i) if (i15) continue
  outer // go to the outer loop

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Introduction to Java Classes and Objects

• Class templates for specifying the state and
  behavior of an object at runtime
• Object instances of a class

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Basic Structures of a Class

• A class consists of variables and methods.
• Example (Right Column)
• One variable firstVariable
• Two method setValue(nv) andgetValue()
• Access variables and methods
• ltObjectgt.ltvariablegt
• ltObjectgt.ltmethodgt(argument)

78
Basic Structures of a Class

• public class FirstClass int firstVariable
  0 public void setValue(int nv)
  firstVariable nv public int getValue()
  return firstVariable

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Basic Structures of a Class
80
The Class Declaration
81
Constructor

• A method in a class that initialize an instance
  of an object before it's used.
• The same name as the class but no return type
• Multiple Constructors the name name but
  different arguments
• Method Overloading
• Java Provides default constructors.
• The special variable, this, can be used inside a
  method to refer to the object instance.

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Member Variables Declaration
83
Instance and Local Variable

• Local variable is defined inside a block of code
  or a method.
• Example (Right Column)
• Instance Variable firstVariable
• Local Variable half

• public int getHalf() int half // local
  variable half firstVariable / 2 return
  half

84
Methods
85
Method Declaration
86
Return a Value from a Method

• Use return operator in the method to return the
  value.
• Methods can return a primitive type or a
  reference type.
• The class of the returned object must be either a
  subclass of or the exact class of the return type.

87
Method Overload

• Signature of a Method return value, name,
  parameter list
• Method Overloading Use the same method name with
  different arguments
• Constructors can also be overloaded.
• this(parameters) Call another constructor
  within a constructor

88
Passing Information into a Method

• Argument types
• primitive and reference data type Yes
• method No
• Argument Names
• Can have the same name as one of the class's
  member variable
• Use this to refer to the member variable
• Primitive arguments are passed by value.
• Reference arguments are passed by reference.

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The Life Cycle of an Object

• Creating Objects
• Using Objects
• Cleaning Up Unused Objects

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Creating Objects

• Rectangle r new Rectangle(5,5,100,200)
• Declaration Rectangle r (Type name)
• Instantiation new
• Allocate memory for the object
• Initialize instance variables
• Call a constructor
• Initialization by Calling a Constructor
• Rectangle(5,5,100,200)

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Using Objects

• Manipulate or inspect its variables
• objectReference.variable
• r.x 50
• r.y 80
• Call its methods
• objectReference.methodName(argumentList)
• r.move(20,30)
• Java provides an access control mechanism whereby
  classes can restrict or allow access to its
  variables and methods.

92
Controlling Access to Members of a Class
93
Private

• class Alpha
• private int iamprivate
• private void privateMethod()
• System.out.println ("privateMethod")

• class Beta
• void accessMethod()
• Alpha a new Alpha()
• a.iamprivate 10
• a.privateMethod()

How About one Alpha object access the private
member of another Alpha object?
94
Protected

• package Greek
• class Alpha
• protected int iamprotected
• protected void protectedMethod()
• System.out.println ("protectedMethod")
  

• package Greek
• class Gamma
• void accessMethod()
• Alpha a new Alpha()
• a.iamprotected 10
  a.protectedMethod()

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Protected (II)

• import Greek.
• package Latin
• class Delta extends Alpha
• void accessMethod(Alpha a, Delta d)
• a.iamprotected 10
• d.iamprotected 10
• a.protectedMethod()
• d.protectedMethod()

96
Public

• package Greek
• public class Alpha
• public int iampublic
• public void publicMethod()
• System.out.println("publicMethod")

• import Greek.
• package Roman
• class Beta
• void accessMethod()
• Alpha a new Alpha()
• a.iampublic 10
  a.publicMethod()

97
Package

• package Greek
• class Alpha
• int iampackage
• void packageMethod()
• System.out.println("packageMethod")

• package Greek
• class Beta
• void accessMethod()
• Alpha a new Alpha()
• a.iampackage 10
• a.packageMethod()

98
Inhereitance in Java

• A mechanism you can use to create a new class by
  extending the definition of another class
• Increase the reusability of codes
• Single Inheritance

99
Simple Class Hierarchy
Object
Vehicle
Building
Car
Bike
House
Office
Van
Truck
100
More About Inheritance

• Use the extends keyword to create a subclass.
• Method Override
• Use method overriding when you need a subclass to
  replace a method of its superclass.
• Define a new method that replaces the superclass
  method that has the same signature.
• Calling Superclass Methods
• super.ltmethodgt(parameters)
• super(parameters) (Calling superclass
  constructors)

101
If-Example

• if (testscore gt 90) grade 'A' else if
  (testscore gt 80) grade 'B' else if
  (testscore gt 70) grade 'C' else if
  (testscore gt 60) grade 'D' else
  grade 'F'

102
Switch-Example (I)

• int month . . .
  switch (month) case 1
  System.out.println("January") break
  case 2 System.out.println("February")
  break case 3 System.out.println(
  "March") break case 4
  System.out.println("April") break
  case 5 System.out.println("May") break
  case 6 System.out.println("June")
  break case 7 System.out.println(
  "July") break case 8
  System.out.println("August") break
  case 9 System.out.println("September")
  break case 10 System.out.println(
  "October") break case 11
  System.out.println("November") break
  case 12 System.out.println("December")
  break

103
Switch-Example (II)

• int monthint numDays. . .switch (month)
  case 1case 3case 5case 7case 8case
  10case 12 numDays 31 break

• case 4case 6case 9case 11 numDays
  30 breakcase 2 if ( ((year 4 0)
  !(year 100 0)) (year 400 0) )
  numDays 29 else numDays 28
  break

104
Array

• Array
• Store lists of values
• Contiguous group of related memory locations
• Have the same name and the same type
• To refer to an element within the array
• a5, a7, aj1
• A subscript may be an integer or an integer
  expression.
• Java arrays always begin with element 0.

105
Arrays (I)

• A single-dimensional array of ints
• int numbers new int10
• int numbers new int10
• A two-dimensional array of ints
• int matrixnew int510
• int matrixnew int510
• Initialize an array explicitly
• int numbers0,1,2,3
• int matrix0,1,0,1,2

106
Arrays(II)

• A one-dimensional array of strings
• String myStrings new String20
• Another way to declare two-dimensional array
• int jnew int5 (j.length 5)j0
  new int4 (j0.length 4)j1 new
  int4
• To get the size of an array
• int q numbers.length
• A method returning an array of ints
• int returnArray() return new int10
• int returnArray() return new int10

107
Declare / Allocate Arrays

• Allocate 12 elements for integer array c
• int c new int12 OR
• int c // Declares the arrayc new
  int12 // Allocates the array
• Initialize an array explicitly
• int numbers0,1,2,3
• To get the size of an array
• int q c.length // q will be 12

108
Passing Arrays to Methods

• Arrays are passed to methods call-by-reference.
• Use the array name as the parameter
• modifyArray(hourlyTemperatures)
• void modifyArray(int b)
• Array elements are passed to methods either
  call-by-value or call-by-reference, dependent on
  their types.

109
A Method Returns an Array

• Use the array name followed by the subscript as
  the parameter
• printElement(a5)
• A method returning an array of ints
• int returnArray() return new int10

110
Multiple-Subscripted Arrays

• Java does not support multiple-subscript
  directly.
• Specify single-subscript arrays whose elements
  are also single-subscript arrays.

111
Multiple-Subscripted Arrays

• Examples
• int b 1, 2, 3, 4
• int bnew int510
• int jnew int5 (j.length 5) j0
  new int4 (j0.length 4) j1
  new int7 (j1.length7)
• How About three or four dimension arrays?

112
Applet Content

• Examples The Spot, Simple, SimpleClick,
  ScrollingSimple Classes
• Interface
• Life Cycle of an Applet
• Methods for MileStones
• Methods for Drawing and Event Handling
• UI Component

113
The Spot Applet

• Subclass another class
• Implement an Interface
• MouseListener

114
The Spot Applet

• Display a small spot when you click over the
  applet with the mouse.
• Take a look at the applet source code

115
Extend a Class

• Applet Inheritance Hierarchy
• Code Reuse
• Responsibility
• Implement certain methods
• Override certain methods
• Responsibility of Applet's subclass
• Implement at least one init, start, or paint

116
Implement an Interface

• An interface defines a protocol of behaviors
  (methods)
• How to get mouse events from AWT?
• Implement the MouseListener interface
• You can implement more than one interface in a
  class.
• If a class implements an interface, the class
  must implement all of the methods in the
  interface.
• Inheritance and Interface

117
The MouseListener Interface

• MouseListener defines the following methods
• mouseClicked(MouseEvent)
• mouseEntered(MouseEvent)
• mouseExited(MouseEvent)
• mousePressed(MouseEvent)
• mouseReleased(MouseEvent)

118
Life Cycle of an Applet(I)

• The Simple Applet
• Loading the Applet
• An instance of the applet is created.
• The applet initializes itself.
• The applet starts running.
• Leaving and Returning to the applet's page
• The applet stops itself.
• The applet starts itself again.

119
Life Cycle of an Applet (II)

• Reloading the Applet Unload and Load
• Unload stop and final cleanup
• Load See "Loading the Applet"
• Quitting the Browser
• stop
• final cleanup

120
Methods for MileStones (I)

• init
• Initialize the applet each time it's loaded (or
  reloaded).
• start
• Start the applet's execution, such as when the
  applet's loaded or when the user revisits a page
  that contains the applet.
• stop
• Stop the applet's execution, such as when the
  user leaves the applet's page or quits the
  browser.
• destroy
• Perform a final cleanup in preparation for
  unloading.

121
Methods for MileStones (II)

• init
• Contain the code that you would normally put into
  a constructor.
• start
• Perform the applet's work or (more likely) starts
  up one or more threads to perform the work.
• If the applet responses to user actions, no need
  for start
• Stop
• Suspend the applet's execution, so that it
  doesn't take up system resources when the user
  isn't viewing the applet's page

122
Methods for Drawing

• The two display methods an applet can override
• paint
• The basic display method. Draw the applet's
  representation within a browser page.
• update
• Use along with paint to improve drawing
  performance.
• The two methods define in AWT (Abstract Window
  Toolkit) Component class.

123
Method for Event Handling

• Applets inherits a group of event-handling
  methods from the Component class.
• Event-Specific Method
• mouseListener....

124
Pre-Made UI Components(I)

• Buttons (java.awt.Button)
• Checkboxes (java.awt.Checkbox)
• Single-line text fields (java.awt.TextField)
• Larger text display and editing areas
  (java.awt.TextArea)
• Labels (java.awt.Label)

125
Pre-Made UI Components(II)

• Lists (java.awt.List)
• Pop-up lists of choices (java.awt.Choice)
• Sliders and scrollbars (java.awt.Scrollbar)
• Drawing areas (java.awt.Canvas)
• Menus (java.awt.Menu, java.awt.MenuItem,
  java.awt.CheckboxMenuItem)
• Containers (java.awt.Panel, java.awt.Window and
  its subclasses)

126
Methods for Using UI

• Container Class
• Contain components
• Use layout managers to control the components'
  onscreen positions
• add
• Adds the specified Component.
• remove
• Removes the specified Component.
• setLayout
• Sets the layout manager.
• The ScrollingSimple Applet

127
Abstract Window Toolkit (AWT)

• Introduction to AWT
• General Rules for Using AWT Components
• Components Introduction
• Layout Manager
• Writing Event Handlers

128
Introduction to AWT

• Provides GUI components such as buttons, lists,
  menus, and text areas.
• Provide containers (such as windows and menu
  bars)
• Provide higher-level components (such as a dialog
  for opening or saving files).

129
AWT Components Inheritance
130
How to Add a Component to a Container

• Components belong to a container.
• Container objects are also components.
• Windows, such as Frames and Dialog, are the
  top-level containers. Don't need to be added to
  containers.
• Using add() to add a component to a container.
• You can't have one component in two containers.

131
What the Component Class Provides

• Basic Drawing Support
• Event Handling
• Appearance control font
• Appearance control color
• Image handling
• Onscreen size an position control

132
Change the Appearance and Behavior of Components

• The appearance of most components is
  platform-specific.
• You can make minor appearance changes, such as
  the font and color.
• Exception Canvas
• Using event handling to change the behaviors of
  components.

133
How to Use Components

• Buttons
• Checkbox
• Choice
• Label
• List
• Menus
• TextAreas and TextFields
• Scrollbars and Scroll Panes

134
How to Use Containers

• Panel
• Frame
• Window
• Dialog
• Canvas

135
Layout Manager

• Layout Manager controls the size and position of
  components in a container.

136
Layout Managers (I)

• The Layout Managers that JDK provides
• FlowLayout
• GridLayout
• BorderLayout
• CardLayout
• GridBagLayout
• Default Layout Manager
• Panel FlowLayout
• Window BorderLayout
• Use setLayout(Layout Manager) to specify the
  layout manager used by a container

137
Layout Managers (II)
138
BorderLayout

• BorderLayout defines five areas north, south,
  east, west, and center.
• Put the space-hungry component in the center.
• Constructors
• BorderLayout()
• BorderLayout(int horizontalGap, int verticalGap)
• Add Components
• add(Direction, Component)

139
CardLayout

• Use to manager two or more components that share
  the same display space.
• Add Components
• add(String name, Component comp)
• Methods to choose components shown in a
  CardLayout
• public void first(Container parent)
• public void next(Container parent)
• public void previous(Container parent)
• public void last(Container parent)
• public void show(Container parent, String name))

140
FlowLayout

• Put components in a row if possible
• Constructors
• FlowLayout()
• FlowLayout(int alignment)
• FlowLayout.LEFT
• FlowLayout.CENTER
• FlowLayout.RIGHT
• FlowLayout(alignment, horizontalGap, verticalGap)
• add(component)

141
GridLayout

• Place components in a grid of cells.
• Constructors
• GridLayout(int rows, int columns)
• GridLayout(rows, column, horizontalGap,
  verticalGap)
• add(component)

142
GridBagLayout

• Place components in a grid of rows and columns,
  allowing specified components to span multiple
  rows or columns.
• Specify layout constraints for each component.
• GridBagLayout gridbag new GridBagLayout()
• GridBagConstraints c new GridBagConstraints()
• setLayout(gridbag)
• gridbag.setConstraints(theComponent, c)
• add(theComponent)

143
GridBagConstraints(I)

• gridx, gridy
• GridBagConstraints.RELATIVE (Default)
• gridwidth, gridheight (Default Value 1)
• GridBagConstraints.REMAINDER
• GridBagConstraints.RELATIVE
• fill
• GridBagConstraints.NONE (Default)
• GridBagConstraints.HORIZONTAL
• GridBagConstraints.VERTICAL
• GridBagConstraints.BOTH

144
GridBagConstraints (II)

• ipadx, ipady (Default Value 0)
• insets (Default Value 0)
• anchor
• GridBagConstraints.CENTER(Default), NORTH,
  NORTHEAST, EAST, SOUTHEAST, SOUTH, SOUTHWEST,
  WEST, NORTHWEST
• weightx, weighty(Default Value 0)

145
More About Layout Manager

• Create a custom layout manager
• Doing without a layout manager (absolute
  positioning)

146
Event (I)

• New event model
• Events are generated by event sources.
• One or more listeners can register to be notified
  about enents of a particular kind from a
  particular source.
• Event handler can be instances of any class.

147
Event (II)

• Three bits of code
• public class MyClass implements
  SomeKindOfListener
• aComponent.addSomeKindOfListener(instanceOfMyClass
  )
• Implementation of the methods in the
  SomeKindOfListener Handling standard AWT events
  (eventstandard.html)

148
More about Event

• Adapters
• MyClass extends MouseAdapter
  .....someObject.addMouseListener(this)
• Inner Class
• MyClass extends Applet .....someObject.addMouse
  Listener(new MyAdapter))...class MyAdapter
  extends MouseAdapter ....

149
Threads of Control

• What Is a Thread
• A Simple Thread Example
• Thread Attributes

150
What Is a Thread

• Definition A thread is a single sequential flow
  of control within a program
• Some texts use the name lightweight process
  instead of thread
• Takes advantage of the resources allocated for
  that program and the program's environment

151
A Simple Thread Example (I)

• class TwoThreadsTest
• public static void main
  (String args)
• new SimpleThread("Jamaica")
  .start()
• new SimpleThread("Fiji").st
  art()
• class SimpleThread extends Thread
  
• public SimpleThread(String
  str)
• super(str)

152
A Simple Thread Example (II)

• public void run()
• for (int i 0 i lt 10
  i)
• System.out.println(i
  " " getName())
• try
• sleep((int)(Math.ra
  ndom() 1000))
• catch
  (InterruptedException e)
• System.out.println("DONE!
  " getName())

153
Thread Body

• All the action takes place in the thread body,
  which is the thread's run() method.
• Two ways to provide run() for a Java thread
• Subclass the Thread class defined in the
  java.lang package and override the run() method
• Provide a class that implements the Runnable
  interface, also defined in the java.lang package

154
Thread State (I)
155
Thread State (II)

• New Thread
• Thread myThread new MyThreadClass()
• Runnable
• myThread.start()
• Not Runnable
• Someone invokes its sleep() method
• Someone invokes its suspend() method
• The thread uses its wait() method
• The thread is blocking on I/O

156
Thread State (III)

• Dead
• natural causes
• public void run()
• by being killed (stopped)
• myThread.stop()

157
Thread State (IV)

• IllegalThreadStateException
• For ExampleIllegalThreadStateException is thrown
  when you invoke suspend() on a thread that is not
  "Runnable"
• The isAlive() Method
• false - thread is either a "New Thread" or "Dead
• true - thread is either "Runnable" or "Not
  Runnable"

158
Thread Priority

• You can also modify a thread's priority with the
  setPriority() method
• The chosen thread will run until one of the
  following conditions is true
• a higher priority thread becomes "Runnable"
• it yields, or its run() method exits
• on systems that support time-slicing, its time
  allotment has expired

159
Working with Shape and Text

• Graphics Contexts
• Graphics Objects
• The Coordinate System
• Drawing Text

160
Related Inheritance Tree
Object
Polygon
Color
Graphics
Component
FontMetrics
Font
161
Graphics Contexts and Graphics Objects

• A graphics context enables drawing on the screen
  in Java.
• A Graphics object manages a graphics context by
  controlling how information is drawn.
• Graphics Objects provide
• Drawing
• Font Manipulation
• Color Manipulation

162
Graphics Object

• Lone argument to the paint() and update() methods
• Support two kinds of drawing
• Primitive Graphics (lines, rectangles, and texts)
• Images
• Provide the current drawing context
• Current drawing area
• Current drawing context

163
The Coordinate System
164
Drawing Text

• First consider whether you can use a
  text-oriented Component, like the Label,
  TextField, or TextArea
• Drawing Text
• drawBytes(byte, length, x, y)
• drawChars(char, length, offset, length, x, y)
• drawString(str, x, y)
• TextXY.java

165
Drawing Text
166
Font Constants and Constructors

• Font Style Constants
• public final static int PLAIN
• public final static int BOLD
• public final static int ITALIC
• Constructor
• public Font (String s, // font nameint
  style, // font styleint size) // font point
  size
• Font Name Courier, Helvetica, TimesRoman

167
Font Methods

• Related Methods in Graphics Class
• public abstract void setFont(Font f)
• Related Methods in Font Class
• public int getStyle()
• public int getSize()
• public String getName()
• public String getFamily()
• public boolean isPlain()
• public boolean isBold()
• public boolean isItalic()

168
FontMetrics (I)

• Getting Information about a Font
• FontDemo.java
• Information about a fonts vertical size
• getAscent(), getMaxAscent()
• getDescent(), getMaxDescent()
• getHeight()
• getLeading()

169
FontMetrics (II)
170
FontMetric (III)

• Information about a fonts horizontal size
• getMaxAdvance()
• bytesWidth(bytes, int, int)
• charWidth(int), charWidth(char)
• charsWidth(char, int, int)
• stringWidth(String)
• getWidths()

171
Constructors

• Public Color (int r, // 0 - 255 red contentint
  g, // 0 - 255 green contentint b // 0 - 255
  blue content)
• Public Color (float r, // 0.0 - 1.0 red
  contentfloat g, // 0.0 - 1.0 green
  contentfloat b // 0.0 - 1.0 blue content)

172
Color Constant and Methods

• Color Constant
• orange, pink, cyan, magenta, yellow, black,
  white, gray, lightGray, darkGray, red, green,
  blue
• public final Static Color
• Related Methods in Color Class
• public int getRed() //Return red content
• public int getGreen() //Return green content
• public int getBlue() //Return blue content
• Related Methods in Graphics Class
• public abstract Color getColor() //Return current
  color
• public abstract void setColor(Color c) //Set
  current color

173
Drawing Shapes

• Lines (drawLine())
• Rectangles (drawRect(), fillRect(), and
  clearRect())
• Raised or lowered rectangles (draw3DRect() and
  fill3DRect())
• Round-edged rectangles (drawRoundRect() and
  fillRoundRect())
• Ovals (drawOval() and fillOval())
• Arcs (drawArc() and fillArc())
• Polygons (drawPolygon() and fillPolygon())

174
Introduction to Exception Handling

• An exception is an event that occurs during the
  execution of a program that disrupts the normal
  flow of instructions.

175
How to Find an Appropriate Exception Handler

• The set of methods in the call stack of the
  method where the error occurred.
• The type of the exception thrown is the same as
  the type of exception handled by the handler.
• The exception handler chosen is said to catch the
  exception.

176
Advantages of Exception Handling

• Separating error handling code from regular
  code
• Propagating errors up the call stack
• Grouping error types and error differentiation

177
Grouping Exception Types
178
Catch or Specify Requirement

• A method need to either catch or specify all
  checked exceptions that can be thrown within the
  scope of the method.
• Exceptions that can be thrown by a method is part
  of the methods public programming interface.
• Exception Classification
• RunTime arithmetic, pointer, indexing exceptions
• Checked

179
Exception Scope

• Exceptions that can be thrown within the scope of
  the method
• Exceptions that are thrown directly by the method
  with Java's throw statement.
• Exceptions that are thrown indirectly by the
  method through calls to other methods

180
Catching and Handling Exceptions (I) -- try

• The try Block
• Enclose the statements that might throw a
  exception within a try block.
• Define the scope of any exception handlers
  associated with it
• try Java statements
• A try statement must be accompanied by at least
  one catch block or one finally block.

181
Catching and Handling Exceptions (II) -- catch

• The catch Block
• Define exception handlers
• try . . . catch
  (SomeThrowableObject variableName) Java
  statements catch (SomeThrowableObject
  variableName) Java statements

182
Catching and Handling Exceptions (III) --finally

• The finally Block
• To clean up the state of the method before
  allowing control to be passed to a different part
  of the program.
• Close files opened
• Eliminate duplicate code

183
Throw Exceptions

• Specify the exceptions thrown by a method
• MethodName throws exception1, exception2...
• public void writeList throws IOException,
  ArrayIndexOutOfBoundsExceptions ..
• Throw a exception
• throw new exception()
• throw new IOException()

184
Images, Animation, Sound

• Loading, Displaying, and Scaling Images
• Introduction to Animation Image Loop
• Graphics Double Buffering
• Using the MediaTracker to Monitor Image Loading
• Using a Separate Thread to Run Animation
• Loading and Playing Audio Clips

185
Loading, Displaying and Scaling Images (I)

• LoadImageAndScale.java
• img getImage(getDocumentBase(), "T1.gif")
• 1st parameter Image location
• 2nd parameter Image file name
• Java supports GIF and JPEG image formats
• img.getWidth(ImageObserver)
• img.getHeight(ImageObserver)

186
Loading, Displaying and Scaling Images (II)

• g.drawImage(img, 1, 1, this)
• drawImage is a Graphics method
• 2nd and 3rd parameters x and y coordinates to
  put the image
• 4th argument ImageObserver
• Let java automatically notify the ImageObserver
  object to update the image as the remainder of
  the image is loaded.
• g.drawImage(img, 1, 200, width2, height2, this)
• 4th and 5th parameters the x, y scaling factors

187
Introduction to AnimationAn Image Loop

• Store images in an array of images
• Use Thread.sleep(sleepTime) to sleep for a
  fraction of a second before displaying the next
  image.
• Flicker
• repaint() gt update() gt paint()
• The update() method will draw a filled rectangle
  the size of the applet in the current background
  color.
• repaint, update, and paint
• One separate thread is started by repaint()

188
Graphics Double Buffering

• Basic Concept
• Create a blank Image
• Draw on the blank Image (Using methods of the
  Graphics class)
• Display the Image
• Create a graphics double buffer
• buffer createImage(width, height)
• gContext buffer.getGraphics()

189
Using the MediaTracker to Monitor Image Loading

• MediaTracker
• Wait for an image or images to load before
  allowing a program to continue
• Determine if an error occurred while loading an
  image
• imageTracker new MediaTracker(ImageObserver)
• Method
• imageTracker.addImage(img, RegisterID)
• imageTracker.waitForID(RegisterID)
• imageTracker.checkID(RegisterID, boolean)
• Override update()

190
Using a Separate Thread to Run an Animation

• Implement interface Runnable
• Implement the run method
• Thread method
• start()
• stop()
• suspend()
• resume()

191
Loading and Playing Audio Clip

• Applet's Play method
• public void play(URL location, String
  soundFileName)
• public void play(URL soundURL)
• AudioClip
• getAudioClip(URL location, String soundFileName)
• play()
• loop()
• stop()

192
Files and Streams

• Loading, Displaying, and Scaling Images
• Introduction to Animation Image Loop
• Graphics Double Buffering
• Using the MediaTracker to Monitor Image Loading
• Using a Separate Thread to Run Animation
• Loading and Playing Audio Clips

193
Stream
A source can be from file, network, memory, or
other programs
194
Algorithm for Read/Write

• Reading
• Open a stream
• While more information
• read information
• close the stream

• Writing
• Open a stream
• While more information
• write information
• close the stream

195
Character Streams
196
Byte Streams
197
Examples

• Basic File I/O -- Copy.java
• Sequential-Access File CreateSeqFile.java,
  ReadSeqFile.java, CreditInquiry.java
• Random-Access File Record.java,
  CreateRandFIle.java, WriteRandFile.java,
  ReadRandFile.java
• TransactionProcessor.java
• FileTest.java

198
Networking

• TCP/UDP
• Port
• Manipulating URLs

199
TCP/UDP

• TCP (Transport Control Protocol)
  connection-based protocol that provides a
  reliable flow of data between two computers.
• UDP (User Datagram Protocol) protocol that sends
  independent packets of data,called datagrams,
  from one computer to another with no guarantees
  about arrival.

200
Port
Socket
Datagram
201
Manipulating URLs

• java.net.URL
• How to open a URL By using a URL as an argument
  to the showDocument method of class AppletContext
• AppletContext Represent the applets environment
• Applet.getAppletContext() Return a AppletContext
  object

202
Read a File From a Server

• URL.openStream() Associate an InputStream with
  the URL
• Use traditional Stream input methods, like
  readLine to read the contents of the file.

203
Establishing a Simple Server (Stream Socket)

• Step1 Create a ServerSocket Object
• ServerSocket s new ServerSocket(port,
  queueLength)
• Step2 Create a Socket and Wait for a Connection
• Socket connect s.accept()
• Step3 Associate Input and Output Stream with the
  Socket
• connect.getInputStream
• connect.getOutputStream
• Step4 Process Connection
• Step5 Close Connection

204
Establishing a Simple Client (Stream Socket)

• Step1 Create a Socket to make connection
• Socket connect new Socket(ServerName, port)
• Step2 Associate Input and Output Stream with the
  Socket
• connect.getInputStream
• connect.getOutputStream
• Step3 Process Connection
• Step4 Close Connection

205
Datagrams

• Set up a DatagramSocket
• Send socket new DatagramSocket()
• Receive socket new DatagramSocket(port)
• Set up a Packet
• Send s new DatagramPacket(.Packet Info..)
• Receive r new DatagramPacket(data, length)
• Send/Receive
• socket.receive(packet)
• socket.send(packet)