大家帮忙看看问题出在哪里？

[hnalenx]

import java.awt.*;
import javax.swing.*;
public class CrossLight extends JPanel{
  private int width=getWidth();
  private int height=getHeight();
  private boolean Red,Yellow,Green;
  private boolean isRed(){
     return Red;
  }
  protected void setRed(boolean Red){
     this.Red=Red;
     repaint();
  }
  protected boolean isYellow(){
     return Yellow;
  }
  protected void setYellow(boolean Yellow){
     this.Yellow=Yellow;
     repaint();
  }
  protected boolean isGreen(){
     return Green;
  }
  protected void setGreen(boolean Green){
     this.Green=Green;
     repaint();
  }
  protected void paintComponent(Graphics g){
    super.paintComponent(g);
    int width_Rect=width/3;
    //int height_Rect=height/2;
    int x_Rect=width/2;
    int y_Rect=height/2;
    int x_Red=x_Rect;
    int y_Red=y_Rect;
    int x_Yellow=x_Rect;
    int y_Yellow=y_Red+width_Rect;
    int x_Green=x_Rect;
    int y_Green=y_Yellow+width_Rect;
    g.setColor(Color.BLACK);
    g.drawRect(x_Rect,y_Rect,width_Rect,3*width_Rect);
    if(Red){
       g.setColor(Color.RED);
       g.fillOval(x_Red,y_Red,width_Rect,width_Rect);
    }
    else{
       g.drawOval(x_Red,y_Red,width_Rect,width_Rect);
    }
    if(Yellow){
       g.setColor(Color.YELLOW);
       g.fillOval(x_Yellow,y_Yellow,width_Rect,width_Rect);
    }
    else{
       g.drawRect(x_Yellow,y_Yellow,width_Rect,width_Rect);
    }
    if(Green){
       g.setColor(Color.GREEN);
       g.fillOval(x_Green,y_Green,width_Rect,width_Rect);
    }
    else{
       g.drawOval(x_Green,y_Green,width_Rect,width_Rect);
    }
  }
  public Dimension getPreferredSize(){
    return new Dimension(60,90);
  }
}
import java.awt.*;
import javax.swing.*;
import java.awt.event.*;
public class ControlLight extends JFrame{
   private JRadioButton jrbRed=new JRadioButton("Red");
   private JRadioButton jrbYellow=new JRadioButton("Yellow");
   private JRadioButton jrbGreen=new JRadioButton("Green");
   private CrossLight light=new CrossLight();
   public ControlLight(){
      JPanel jpbutton=new JPanel(new FlowLayout(FlowLayout.CENTER,2,0));
      jpbutton.add(jrbRed);
      jpbutton.add(jrbYellow);
      jpbutton.add(jrbGreen);
      ButtonGroup group=new ButtonGroup();
      group.add(jrbRed);
      group.add(jrbYellow);
      group.add(jrbGreen);
      add(jpbutton,BorderLayout.SOUTH);
      add(light);
      jrbRed.addActionListener(new ActionListener(){
          public void actionPerformed(ActionEvent e){
             light.setRed(true);
          }
      });
      jrbYellow.addActionListener(new ActionListener(){
          public void actionPerformed(ActionEvent e){
             light.setYellow(true);
          }
      });
      jrbGreen.addActionListener(new ActionListener(){
          public void actionPerformed(ActionEvent e){
             light.setGreen(true);
          }
      });
   }
   public static void main(String[] args){
      ControlLight frame=new ControlLight();
      frame.setTitle("ControlLight");
      frame.pack();
      frame.setLocationRelativeTo(null);
      frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
      frame.setVisible(true);
  }
}

大家帮我看看为什么CrossLight的实例在编译运行后主类中显示不出来？

[xiesisi3]

package defaultpackage;

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

public class CrossLight extends JPanel {
	/**
	 * 
	 */
	private static final long serialVersionUID = 3545860909727139358L;

	private int width = 200;

	private int height = 200;

	private boolean Red, Yellow, Green;
	
	public CrossLight(){
		this.setSize(200, 200);
		this.setLocation(100, 100);
		setVisible(true);
	}

	private boolean isRed() {
		return Red;
	}

	protected void setRed(boolean Red) {
		this.Red = Red;
		repaint();
	}

	protected boolean isYellow() {
		return Yellow;
	}

	protected void setYellow(boolean Yellow) {
		this.Yellow = Yellow;
		repaint();
	}

	protected boolean isGreen() {
		return Green;
	}

	protected void setGreen(boolean Green) {
		this.Green = Green;
		repaint();
	}

	public void paint(Graphics g) {
		super.paintComponent(g);
		int width_Rect = width / 3;
		// int height_Rect=height/2;
		int x_Rect = width / 2;
		int y_Rect = height / 2;
		int x_Red = x_Rect;
		int y_Red = y_Rect;
		int x_Yellow = x_Rect;
		int y_Yellow = y_Red + width_Rect;
		int x_Green = x_Rect;
		int y_Green = y_Yellow + width_Rect;
		g.setColor(Color.BLACK);
		g.drawRect(x_Rect, y_Rect, width_Rect, 3 * width_Rect);
		if (Red) {
			g.setColor(Color.RED);
			g.fillOval(x_Red, y_Red, width_Rect, width_Rect);
			repaint();
		} else {
			g.drawOval(x_Red, y_Red, width_Rect, width_Rect);
		}
		if (Yellow) {
			g.setColor(Color.YELLOW);
			g.fillOval(x_Yellow, y_Yellow, width_Rect, width_Rect);
		} else {
			g.drawRect(x_Yellow, y_Yellow, width_Rect, width_Rect);
			repaint();
		}
		if (Green) {
			g.setColor(Color.GREEN);
			g.fillOval(x_Green, y_Green, width_Rect, width_Rect);
		} else {
			g.drawOval(x_Green, y_Green, width_Rect, width_Rect);
			repaint();
		}
	}

	public Dimension getPreferredSize() {
		return new Dimension(60, 90);
	}
	
	public static void main(String[] args) {
		CrossLight cl = new CrossLight();
		cl.setRed(true);
		JFrame jf = new JFrame();
		jf.setLocation(300, 300);
		jf.setSize(300, 300);
		jf.add(cl);
		jf.setVisible(true);
	}
}
package defaultpackage;

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

public class ControlLight extends JFrame {
	/**
	 * 
	 */
	private static final long serialVersionUID = 7839937459494006808L;

	private JRadioButton jrbRed = new JRadioButton("Red");

	private JRadioButton jrbYellow = new JRadioButton("Yellow");

	private JRadioButton jrbGreen = new JRadioButton("Green");

	private CrossLight light = new CrossLight();

	public ControlLight() {
		JPanel jpbutton = new JPanel(new FlowLayout(FlowLayout.CENTER, 2, 0));
		jpbutton.add(jrbRed);
		jpbutton.add(jrbYellow);
		jpbutton.add(jrbGreen);
		ButtonGroup group = new ButtonGroup();
		group.add(jrbRed);
		group.add(jrbYellow);
		group.add(jrbGreen);
		setSize(500, 500);
		setLayout(new BorderLayout());
		add(jpbutton, BorderLayout.NORTH);
//		light.setRed(true);
		add(light, BorderLayout.CENTER);
		jrbRed.addActionListener(new ActionListener() {
			public void actionPerformed(ActionEvent e) {
				light.setRed(true);
			}
		});
		jrbYellow.addActionListener(new ActionListener() {
			public void actionPerformed(ActionEvent e) {
				light.setYellow(true);
			}
		});
		jrbGreen.addActionListener(new ActionListener() {
			public void actionPerformed(ActionEvent e) {
				light.setGreen(true);
			}
		});
	}

	public static void main(String[] args) {
		ControlLight frame = new ControlLight();
		frame.setTitle("ControlLight");
//		frame.pack();
		frame.setLocationRelativeTo(null);
		frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
		frame.setVisible(true);
	}
}

我改了一下，现在可以显示了。

[999朵玫瑰]

serialVersionUID

[hnalenx]

#1楼的大哥给我讲一下原因吧，这样改一下我也不知道错在哪里，麻烦了！！

[pywepe]

顶一下吧

[huangwj20042008]

int width_Rect=width/3;
//int height_Rect=height/2;
int x_Rect=width/2;
int y_Rect=height/2;

改成下面这样：
int width_Rect=getWidth()/3;
//int height_Rect=height/2;
int x_Rect=getWidth()/2;
int y_Rect=getHeight()/2;

[子龙奶爸]

顶一下吧

[hnalenx]

huangwj20042008同志，给我解析一下为什么我向下面这样写
int width_Rect=width/3;
//int height_Rect=height/2;
int x_Rect=width/2;
int y_Rect=height/2;
所获取的值是空啊?麻烦了！！

[huangwj20042008]

[Quote=引用 9 楼 hnalenx 的回复:]
huangwj20042008同志，给我解析一下为什么我向下面这样写
int width_Rect=width/3;
    //int height_Rect=height/2;
    int x_Rect=width/2;
    int y_Rect=height/2;
所获取的值是空啊?麻烦了！！

[/Quote]

width，height是在初始化的时候赋的值，而构建panel的时候，getWidth()，getHeight()返回的是0。

[SambaGao]

做swing的越来越多了。
最近java 6 update 18 对swing优化了很多。大家可以去看看。

[岁月之梦]

swing 忘光了 sorry 给点分让我升星星吧！

[cbajing]

swing..............

[zuoyuxing]

顶....我现在还看不太懂，呵呵