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An Introduction

Java Short Course

Day-

J

Outline

• Applets Once again
• GUI-Components
• Components hierarchy
• Packages
• The Java AWT Package
• Exploring Component Classes
• Creating and Using Components
• Exploring Components Properties
• Using JBuilder7 design tool

Packages

• Packages

 java.awt  javax.swings

• java.awt pacakge

 Abstract Windowing Kit  GUI-Components are drawn according to the underlying windowing system  Initial set of Components developed  AWT Components  Buttons  Text Fields  Labels  Text Areas  Check Boxes  Menus  Radio Buttons  Canvases  Lists  Scroll Panes  Choices

First Button

• Two simple steps

 Create a Button

 Add button to the applet

 Don’t Forget to import the awt package.

• Step-

public Button firstButton = new Button(“ Click It ”);

• Step-

add(firstButton);

Button applet output

• Button Applet

Adding few more buttons

import java.awt.*;

import java.applet.*;

public class ButtonApplet extends Applet{

//creating the button component

public Button firstButton = new Button(“One”);

public Button secondButton = new Button(“Two”);

public Button thirdButton = new Button(“Threet”);

public void init( ){

//adding to the applet

add(firstButton); add(secondButton); add(thirdButton); }

}

Layout Managers

• How your components should be organized

 Layout Managers draw place your components at relative positions

 Absolute position can cause problems

 Necessary for application intended for different platforms

 Layout Managers are classes

 AWT Layout Managers

 Flow Layout  GridLayout  Border Layout  CardLayout  GridBagLayout  Null layout

 So how did the previous applet worked

 The default layout manager

Using Layout managers

• Few Simple Steps

 Prepare your container

 Create the container class e.g. applet  Set layout

 Create instance of a Components

 Set Initial conditions e.g. titles, x y position, size etc..

 Add component to the container

• Setting layout

 The setLayout method

setLayout(Object of a Layout Class)

 Inherited from Applet class

Flow Layout…cont..

• Example-

 Using Flow Layout constructor 1

import java.awt.; import java.applet.;

public class flowLayoutTest extends Applet{

public FlowLayout myFlowLayout=new FlowLayout(); Button B=new Button(“Click It”);

public void init(){ setLayout(myFlowLayout);

add(B); } }

Flow layout cont..

• Example-

 Using a different constructor

import java.awt.; import java.applet.;

public class flowLayoutTest extends Applet{

public FlowLayout

myFlowLayout=newFlowLayout(FlowLayout.RIGHT);

Button B=new Button(“Click It”);

public void init(){ setLayout(myFlowLayout); add(B); } }

Using Labels

• String for descriptions or decoration
• Constructors

 public Label()

 public Label( String text)

 public Label( String text, int alignment)

• Alignments

 Label.LEFT

 Label.RIGHT

• Important methods

 coid setText(String text) //to set the label text

 String getText() // to get the label text

 void setAlignment(int Alignment) //set alignment of the label

 public int getAlignment() // get alignment of the label

Labels..

• Example-

 A label for a button import java.awt.; import java.applet.;

public class flowLayoutTest extends Applet{

public FlowLayout myFlowLayout= newFlowLayout((FlowLayout.Right );

Label label_save=new Label( “Save”); Button B=new Button(“Save”);

public void init(){

setLayout(myFlowLayout); add(label_save); add(B); }}

Using Text Areas

• Multi-line input component
• Constructors

 public TextArea()

 Creates an empty text area with default size (9 rows,47 columns)

 public TextArea(Strig initialText)

 Creates a text area and displays the given text

 public TextArea(int numrows,int numcolumns)

 Creates a text area according to the given number of rows and coumns

 public TextArea(String initialText,int numRows,int numcolumns)

• Important methods

 pubic void appendText(String text)

 Adds text at the end of the current text in the text area

 public void insert(String text,int position)

 Adds text at specified character position

 public void replaceText(String text,int start,int end)

Event Handling

• Events are raised when

 The state of a component is changed

 A button click  Clicking a check box

 User performs some action on a component

 Writing text to a field  Clicking on the applet surface

• Handling events

 Interfaces

 action() method

 Depricated method previously used for handling events  Cannot deal all sorts of events  Syntax public boolean action(Event evnt, Object obj){ -------code to perform some actions----------- }