gui swing and awt

8/3/2019 GUI Swing and AWT

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Java

GUI building with the AWT


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AWT (Abstract Window Toolkit)

Present in all Java implementations

Described in (almost) every Java textbook Adequate formany applications

Uses the controls defined byyourOS

therefore it's "least common denominator" Difficult to build an attractive GUI

import java.awt.*;


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Swing

Requires Java 2 ora separate (huge)

download

More controls, and they are more flexible

Gives a choice of look and feel packages

Much easierto build an attractive GUI import javax.swing.*; // Mac or PCimport com.sun.java.swing.*; // UNIX


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Swingvs. AWT

Swing is biggerand slower

Swing is more flexible and betterlooking Swing and AWT are incompatible--you can

use either, but you cant mix them

Learning the AWT is a good start on learningSwing

AWT: Button b = new Button (OK);

Swing: Jbutton b = new Jbutton(OK);


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To builda GUI...

Make somewhere to display things--a

Frame, a Window, oran Applet

Create controls (buttons, text areas, etc.)

Add yourcontrols to yourdisplay area

Arrange, orlay out, yourcontrols Attach Listeners actions to yourcontrols


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Containers andComponents

The job of a Container is to hold and displayComponents. A Container is also aComponent

Some common subclasses ofComponent areButton, Checkbox, Label, Scrollbar,

TextField, and TextArea Some Container subclasses are Panel (and

Applet), Window, and Frame


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To Create A Frame

import java.awt.*; Frame newFrame = new Frame( );

class MyFrame extends Frame { }

We can add components to the Frame

Its best to add components in init( )


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Some types ofcomponents


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10

CreatingComponents

Swing

// Create a button with text OK

JButton jbtOK = new JButton("OK");

// Create a label with text "Enter your name: "

JLabel jlblName = new JLabel("Enter your name: ");

// Create a text field with text "Type Name Here"

JTextField jtfName = new JTextField("Type Name Here");

// Create a check box with text bold

JCheckBox jchkBold = new JCheckBox("Bold");

// Create a radio button with text red

JRadioButton jrbRed = new JRadioButton("Red");

// Create a combo box with choices red, green, and blue

JComboBox jcboColor = new JComboBox(new String[]{"Red",

"Green", "Blue"});

Button

Label

Text

field

Check

Box

Radio

Button

Combo

Box


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Creatingcomponents

AWT Label lab = new Label (Hi, Dave!");

Button but = new Button ("Click me!");

Checkbox toggle = new Checkbox (toggle");

TextField txt =

new TextField (Initial text.", 20);

Scrollbar scrolly = new Scrollbar

(Scrollbar.HORIZONTAL, initialValue,bubbleSize, minValue, maxValue);


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Addingcomponents to the Frame

class MyApplet extends Applet {

public void init () {

add (lab); // same as this.add(lab)

add (but);

add (toggle);

add (txt);

add (scrolly);


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Arrangingcomponents

EveryContainer has a layout manager

The default layout fora Frame is FlowLayout

We can set it explicitly withsetLayout (new FlowLayout( ));

We can change it to some otherlayout manager


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FlowLayout

Use add (component); to add to acomponent using a FlowLayout

Components are added left-to-right

If no room, a new row is started

Exact layout depends on size of Frame Components are made as small as possible

FlowLayout is convenient but often ugly


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BorderLayout At most five components

can be added

Ifyou want more

components, add a Panel,

then add components to it.

setLayout (newBorderLayout());

add (BorderLayout.NORTH, new Button(NORTH));


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BorderLayout with five Buttons

public void init() {

setLayout (new BorderLayout ());add (BorderLayout.NORTH, new Button ("NORTH"));add (BorderLayout.SOUTH, new Button ("SOUTH"));add (BorderLayout.EAST, new Button ("EAST"));add (BorderLayout.WEST, new Button ("WEST"));

add (BorderLayout.CENTER, new Button ("CENTER"));}


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Usinga Panel

panel p = new Panel(); add (BorderLayout.SOUTH, p);

p.add (new Button (Button 1));

p.add (new Button (Button 2));


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Makingcomponents active

Most components alreadyappearto do

something--buttons click, text appears

To associate an action with a component, attach

a listenerto it

Components send events, listeners listen for

events

Different components may send different

events, and require different listeners


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Listeners

Listeners are interfaces, not classes

class MyButtonListener implementsActionListener {

An interface is a group of methods that must

be supplied

When you sayimplements, you arepromisingto supply those methods


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Writinga Listener

Fora Button, you need an ActionListener

b1.addActionListener(new MyButtonListener ( ));

An ActionListener must have anactionPerformed( ) method

public voidactionPerformed(ActionEvent e) {}


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MyButtonListenerpublic void init () {

...

b1.addActionListener (new MyButtonListener ());}

class MyButtonListener implements ActionListener {public void actionPerformed (ActionEvent e) {

showStatus ("Ouch!");}

}


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Listeners for TextFields

An ActionListener listens forhitting thereturn key

An ActionListener demandspublic void actionPerformed (ActionEvent e)

use getText( ) to get the text

A TextListener listens forany and all keys

A TextListener demandspublic void textValueChanged(TextEvent e)


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Summary I:

Buildinga GUI

Create A Frame by extending Frame

Choose a layout manager (FlowLayout isthe default)

Create more complex layouts by putting

Panels in the Frame; each Panel can haveits own layout manager

Create othercomponents and add them to

whichever Panels you like


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Summary II:

Buildinga GUI

Foreach active component, look up what

kind ofListeners it can have

Create (implement) the Listeners, typicallyone Listenerperactive component

Foreach Listener you implement, supplythe methods that it requires

gui swing and awt

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