Java Swing

One of the most important features of Java is its ability to draw

graphics.

AWT to Swing

• AWT: Abstract Window Toolkit• import java.awt.*

• Swing: new with Java2• import javax.swing.* extends AWT

• Depends less on underlying platform

• Many more predefined GUI components• Event listeners

• API: • http://docs.oracle.com/javase/8/docs/api/

GUI Component API

• Java: GUI component = class

• Properties

• Methods

• Events

JButton

Using a GUI Component

1. Create it• Instantiate object: b = new JButton(“press me”);

2. Configure it• Properties: b.text

• Methods: b.setText(“press me”); //set this way

3. Add button b to panel• panel.add(b);

4. Listen to it• Events: Listeners

JButton

Anatomy of an Application GUI

JPanel

JButton

JFrame

JLabel

GUI Internal structure

JFrame

JPanel

JButton JLabel

containers

Using a GUI Component 2

1. Create it

2. Configure it

3. Add children (if container)

4. Add to parent (if not JFrame)

5. Listen to it

orderimportant

JPanel

JButton

Listener

JFrame

JLabel

Add from bottom up

• Create:• Frame• Panel• Components• Listeners

• Add: (bottom up)• listeners into components• components into panel• panel into frame

Frames

• Swing version JFrame (extends AWT’s frame)

• Import javax.swing (‘x’ – extension package)

• Default size is 0x0 pixels

DEMO FrameTest.java

Frames

• Need to extend class

• Override constructor for size desired.

• Select behavior on Close (for example, exit)

• Starts invisible, must show

DEMO SimpleFrameTest.java

Frames

• Only a few methods to change look• Inherits methods from superclasses

– dispose – closes window and reclaims resources– setIconImage - used when window is minimized– setTitle – for menu bar of window– setResizable – takes boolean to enable/disable user’s

ability to resize window– setLocation – position component– setBounds – size and position component

DEMO SimpleFrameTest2.java

Inheritance Chain

JFrameFrameWindow

Container

JPanelJComponent

Component

Object

Panels

• Draw on a panel, which is added to frame– Specifically to the content pane of the frame

• Displays information – Draw strings– Draw graphical elements

• Add components into content pane (they are containers)

SomeComponent c = new …Container contentPane = frame.getContentPane();contentPane.add (c);

Application Code

import javax.swing.*;

class hello {

public static void main(String[ ] args) {

JFrame f = new JFrame(“title”); JPanel p = new JPanel(); JButton b = new JButton(“press me”);

p.add(b); // add button to panel f.setContentPane(p); // add panel to frame

f.show();}

}

press me

Subclasses

• Extend JPanel• Override paintComponent method in that class to do

graphics

class MyPanel extends Jpanel { public void paintComponent (Graphics

g) { //code for drawing goes here }

DEMO NotHelloWorld.java

Painting…

• Never call paintComponent – Event handler notifies component to paint itself

whenever needed• Resizing, minimizing, overlapping windows, etc.

– If you need to force repainting, call repaint instead

Subclasses cont.

class MyPanel extends Jpanel { public void paintComponent (Graphics g) { super.paintComponent (g); //superclass

does job

//code for drawing goes here g.drawString (“Java is COOL!”, 75, 100); }

DEMO NotHelloWorld.java