Understanding AWT Components and Layout Managers in Java GUI Development, Slides of Java Programming

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ava - programming

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

Container-Non-Container Components

JPanel

JPanel

JButton JButton

JTextArea

JFrame

Combination

JPanel

JButton

JLabel

JButton JButton

JTextArea

AWT Components

Swing

Components

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); }

}

Why Buttons are in one row?

How to control them?

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

Flow Layout

• Adds components in a row
• Starts from left
• Treats container as set of rows
• Height of row is defined by the height of components
• Default alignment is left
• Can also start from right or center
• The constructor

 pulic FlowLayout()

 Public FlowLayout(int alignment) //FlowLayout.LEFT

 Public FlowLayout(int alignement,int hgap,vgap)

• Setting layout
• Step-

Public FlowLayout myFlowLayout=new FlowLayout();

• Step-

setLayout(myFlowLayout)

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); } }