"Fundamentals of Java language Programming"--event-driven programming--understanding listeners, registering, and handling events

Use of the listener for the first time

Listener: Is an instance of a listener interface and must be registered on the source object

Listener Implementation Listener Interface

Create listener registers to source object above

Registration method: Call Source.addactionlistener () to register

First step (70 lines): Create Enlargelistener class to implement ActionListener interface
Step Two (28 lines): New one listener, then register to button1
Step three (54 lines): Create a enlarge method to be called
Fourth step (74 lines): Overwrite the Actionperformed method in the interface once the operation is monitored to perform the next sentence called the Enlarge method
Fifth step (line 71): to allow actionperformed to access the Enlarge method, define the class as inner class

Package Chapter16;import Java.awt.borderlayout;import Java.awt.graphics;import java.awt.event.actionevent;import Java.awt.event.actionlistener;import Javax.swing.jbutton;import Javax.swing.jframe;import javax.swing.JPanel;@ Suppresswarnings ("Serial") public class ControlCircle1 extends JFrame {private Circle1 circle = new Circle1 (20);//must be placed outside the method So that the Enlargelistener class can access the variable circleprivate JButton button1 = new JButton ("enlarge");p rivate JButton button2 = new JButton (" Shrink ");p ublic ControlCircle1 () {JPanel P1 = new JPanel ();p 1.add (button1);p 1.add (button2); Add (Circle, Borderlayout.center); Add (P1, Borderlayout.south); Button1.addactionlistener (new Enlargelistener ());//Second step: New One listener , and then register to button1 on Button2.addactionlistener (New Shrinklistener ());} public static void Main (string[] args) {ControlCircle1 a = new ControlCircle1 (); A.setdefaultcloseoperation (Jframe.exit_ On_close); A.setlocationrelativeto (null); A.setvisible (true); A.settitle ("displayshow"); A.setsize (300, 300);} Class Circle1 extends JPanel {PRivate int radius = 5;public circle1 () {}public circle1 (int radius) {This.radius = radius;} public void enlarge () {///Third step: Create enlarge method to be called radius +=20;repaint ();} public void shrink () {radius-=5;repaint ();} protected void Paintcomponent (Graphics g) {super.paintcomponent (g); G.drawoval (GetWidth ()/2-radius, getheight ()/2-r adius,2 * radius, 2 * radius);}} Class Enlargelistener implements ActionListener {//First step: Create Enlargelistener Class Implementation ActionListener interface// Fifth step: In order for actionperformed to access the Enlarge method, define the class as Inner class@overridepublic void actionperformed (ActionEvent e) {// Fourth step: Overwrite the Actionperformed method in the interface once the operation is monitored to perform the next sentence called the Enlarge method Circle.enlarge ();//handling event}}class Shrinklistener implements actionlistener{@Overridepublic void actionperformed (ActionEvent e) {Circle.shrink ();}}}

The enlarge and shrink keys are to control the enlargement and reduction of the circle

"Fundamentals of Java language Programming"--event-driven programming--understanding listeners, registering, and handling events