按照你的要求，写出的程序如下：
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import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Graphics;
import java.awt.event.ItemEvent;
import java.awt.event.ItemListener;
import javax.swing.JComboBox;
import javax.swing.JFrame;
import javax.swing.JPanel;
public class TrafficLight {
JFrame jf=new JFrame("Traffic Light");
JPanel jp=new JPanel();
JComboBox jcb=new JComboBox();
public TrafficLight(){
jcb.addItem("红灯");
jcb.addItem("黄灯");
jcb.addItem("绿灯");
jcb.addItemListener(new JComboBoxListener());
jf.add(jcb,BorderLayout.NORTH);
jf.add(jp,BorderLayout.CENTER);
jf.setSize(400,400);
jf.setVisible(true);
jf.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
}
public static void main(String[] args) {
// TODO Auto-generated method stub
new TrafficLight();
}
class JComboBoxListener implements ItemListener{
@Override
public void itemStateChanged(ItemEvent ie) {
Graphics g=jf.getGraphics();
if(ie.getItem().equals("红灯")){
g.setColor(Color.RED);
g.fillOval(200, 200, 100, 100);
}else if(ie.getItem().equals("黄灯")){
g.setColor(Color.YELLOW);
g.fillOval(200, 200, 100, 100);
}else if (ie.getItem().equals("绿灯")){
g.setColor(Color.GREEN);
g.fillOval(200, 200, 100, 100);
}
}
}
}
import java.awt.Color;
import java.awt.Container;
import java.awt.Dimension;
import java.awt.FlowLayout;
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;
public class Way extends JPanel {
JButton red;
public Way() {
red= new JButton("换灯");
setBackground(Color.yellow);
setSize(new Dimension(320, 260));
setPreferredSize(new Dimension(320, 260) );
JPanel btnPanel = new JPanel();
btnPanel.setLayout(new FlowLayout());
red.setLayout(new FlowLayout());// 将单选按钮加入按钮面板
btnPanel.add(red);
add(red);
}
private void lightRed(Graphics g) {
g.setColor(Color.red);
g.fillOval(getWidth() / 2, 30, 15, 15);
g.setColor(Color.black);
g.fillOval(getWidth() / 2, 50, 15, 15);
g.fillOval(getWidth() / 2, 70, 15, 15);
}
private void lightYellow(Graphics g) {
g.setColor(Color.yellow);
g.fillOval(getWidth() / 2, 50, 15, 15);
g.setColor(Color.black);
g.fillOval(getWidth() / 2, 30, 15, 15);
g.fillOval(getWidth() / 2, 70, 15, 15);
}
private void lightGreen(Graphics g) {
g.setColor(Color.green);
g.fillOval(getWidth() / 2, 70, 15, 15);
g.setColor(Color.black);
g.fillOval(getWidth() / 2, 30, 15, 15);
g.fillOval(getWidth() / 2, 50, 15, 15);
}
protected void paintComponent(Graphics g) {
super.paintComponents(g);
Way a = new Way();
g.clearRect(0, 0, getWidth(), getHeight());
g.drawRect(getWidth() / 2, 30, 30, 80);
red.addActionListener(new ActionListener() {
int f1 = 0;
public void actionPerformed(ActionEvent e) {
Graphics g = getGraphics();
switch (f1) {
case 0:
a.lightRed(g);
break;
case 1:
a.lightYellow(g);
break;
case 2:
a.lightGreen(g);
break;
}
f1++;
if(f12) f1=0;
};
});
}
public static void main(String[] args) {
JFrame fr = new JFrame("邮件界面模拟");
fr.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); // 点击x结束程序
Container contentPane = fr.getContentPane();
// 得到窗口内容面板
contentPane.add(new Way());
fr.pack();
fr.setVisible(true); // 设置窗口可见
}
}大致帮你改了下，不知道符合不符合你的要求，有问题请追问
按照你的要求编写的红绿灯程序，你看看吧，比较简单。
完整的程序如下：
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import java.awt.Graphics;
public class TrafficLight extends JFrame{
JRadioButton jrbYellow,jrbGreen,jrbRed;
int flag=0;
jpNewPanel jpNewPanel;
public static void main(String[] args){
TrafficLight frame=new TrafficLight();
frame.setSize(500,200);
frame.setLocationRelativeTo(null);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setTitle("TrafficLight");
frame.setVisible(true);
}
public TrafficLight(){
jpNewPanel=new jpNewPanel();
add(jpNewPanel,BorderLayout.CENTER);
JPanel jpRadioButtons=new JPanel();
jpRadioButtons.setLayout(new GridLayout(1,3));
jpRadioButtons.add(jrbYellow=new JRadioButton("Yellow"));
jpRadioButtons.add(jrbGreen=new JRadioButton("Green"));
jpRadioButtons.add(jrbRed=new JRadioButton("Red"));
add(jpRadioButtons,BorderLayout.SOUTH);
ButtonGroup group=new ButtonGroup();
group.add(jrbYellow);
group.add(jrbGreen);
group.add(jrbRed);
jrbYellow.addActionListener(new ActionListener(){
public void actionPerformed(ActionEvent e){
flag=2;
jpNewPanel.repaint();
}
});
jrbGreen.addActionListener(new ActionListener(){
public void actionPerformed(ActionEvent e){
flag=1;
jpNewPanel.repaint();
}
});
jrbRed.addActionListener(new ActionListener(){
public void actionPerformed(ActionEvent e){
flag=3;
jpNewPanel.repaint();
}
});
}
class jpNewPanel extends JPanel{
protected void paintComponent(Graphics g){
super.paintComponent(g);
g.drawRect(0,0,40,100);
g.drawOval(10,10,20,20);
g.drawOval(10,40,20,20);
g.drawOval(10,70,20,20);
if(flag==1){
g.setColor(Color.GREEN);
g.fillOval(10, 70, 20, 20);
}
else if(flag==2){
g.setColor(Color.YELLOW);
g.fillOval(10, 40, 20, 20);
}
else if(flag==3){
g.setColor(Color.RED);
g.fillOval(10, 10, 20, 20);
}
}
}
}
//按回车键就可以
import java.awt.event.KeyAdapter;
import java.awt.event.KeyEvent;
import javax.swing.JFrame;
import javax.swing.JLabel;
public class Print {
public static void main(String[] args) {
JFrame jFrame = new JFrame ();
final JLabel jLabel = new JLabel ("按回车键！");
jFrame.setLayout(null);
jLabel.setBounds(80,50,500,80);
jFrame.add(jLabel);
jFrame.setSize(200, 200);
jFrame.setLocation(200, 300);
jFrame.setVisible(true);
jFrame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
jFrame.addKeyListener(new KeyAdapter () {
int n = 0;
public void keyPressed(KeyEvent e) {
int keyCode = e.getKeyCode();
if (keyCode == KeyEvent.VK_ENTER) {
n++;
if (n == 1)
jLabel.setText("绿");
else if (n == 2) {
jLabel.setText("红");
} else if (n == 3) {
jLabel.setText("黄");
n = 0;
}
}
}
});
}
}
