Question

java listener actionperformed 问题

运行不起来 帮忙看一下吧 谢谢你们了
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
public class SimpleGui3C extends JFrame implements ActionListener{
JFrame frame;
public static void main(String[] args) {
// TODO Auto-generated method stub
SimpleGui3C gui=new SimpleGui3C();
gui.go();
}

public void go(){
frame=new JFrame();
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

JButton button= new JButton("change colours");
button.addActionListener(this);

MyDrawPanel drawPanel=new MyDrawPanel();

frame.getContentPane().add(BorderLayout.SOUTH,button);
frame.getContentPane().add(BorderLayout.CENTER,drawPanel);

frame.setSize(300,300);
frame.setVisible(true);

public void actionPerformed(ActionEvent event){
frame.repaint();
}
}
}
另一个类
import java.awt.Color;
import java.awt.GradientPaint;
import java.awt.Graphics;
import java.awt.Graphics2D;

import javax.swing.JPanel;

class MyDrawPanel extends JPanel {
private static final long serialVersionUID = 1L;
public void paintComponent(Graphics g){
Graphics2D g2d=(Graphics2D) g;
GradientPaint gradient=GradientPaint(50,50,Color.blue,150,150,Color.orange);
g2d.setPaint(gradient);
g2d.fillOval(70,70,100,100);
}
编译都没有通过 public void actionPerformed(ActionEvent event){
frame.repaint();
}说 void is an invalid type for the variable actionPerformed

Answer 1

public class SimpleGui3C extends JFrame implements ActionListener {
/**
*
*/
private static final long serialVersionUID = 1L;
JFrame frame;

public static void main(String[] args) {
// TODO Auto-generated method stub
SimpleGui3C gui = new SimpleGui3C();
gui.go();
}

public void go() {
frame = new JFrame();
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

JButton button = new JButton("change colours");
button.addActionListener(this);

MyDrawPanel drawPanel = new MyDrawPanel();

frame.getContentPane().add(BorderLayout.SOUTH, button);
frame.getContentPane().add(BorderLayout.CENTER, drawPanel);

frame.setSize(300, 300);
frame.setVisible(true);
}

public void actionPerformed(ActionEvent event) {
frame.repaint();
}
}

另一个类
import java.awt.Color;
import java.awt.GradientPaint;
import java.awt.Graphics;
import java.awt.Graphics2D;

import javax.swing.JPanel;

public class MyDrawPanel extends JPanel {
private static final long serialVersionUID = 1L;

public void paintComponent(Graphics g) {
Graphics2D g2d = (Graphics2D) g;
GradientPaint gradient = new GradientPaint(50, 50, Color.blue, 150,
150, Color.orange);
g2d.setPaint(gradient);
g2d.fillOval(70, 70, 100, 100);
}
}

自己对照看看哪儿不同！

Answer 2

import javax.swing.*;
import java.awt.*;
import java.awt.event.*;

public class SimpleGui3C extends JFrame implements ActionListener{
JFrame frame;
public static void main(String[] args) {
// TODO Auto-generated method stub
SimpleGui3C gui=new SimpleGui3C();
gui.go();
}

public void go(){
frame=new JFrame();
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

JButton button= new JButton("change colours");
button.addActionListener(this);

MyDrawPanel drawPanel=new MyDrawPanel();

frame.getContentPane().add(BorderLayout.SOUTH,button);
frame.getContentPane().add(BorderLayout.CENTER,drawPanel);

frame.setSize(300,300);
frame.setVisible(true);

}
public void actionPerformed(ActionEvent event){
frame.repaint();
}

}

class MyDrawPanel extends JPanel {
private static final long serialVersionUID = 1L;
public void paintComponent(Graphics g){
Graphics2D g2d = (Graphics2D) g;
GradientPaint gradient = new GradientPaint(50,50,Color.blue,150,150,Color.orange);
g2d.setPaint(gradient);
g2d.fillOval(70,70,100,100);
}
}

点击按钮没什么反应！

Answer 3

ewFVv