相同的程序，可能出现不同的结果，是怎么回事？

Question

这个程序，出现无规律的情况，有时第一次正常，有时第一次不正常，有时要运行几次又正常，不知何因？
本来正常情况下，几个buuton都应出来的，可是有时出来，有时不显示出来。代码如下：
import java.awt.Frame;
import java.awt.Button;
import java.awt.BorderLayout;
import java.awt.Color;
import java.applet.Applet;
import java.awt.Graphics;
import java.applet.Applet;
import java.awt.FlowLayout;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import java.awt.event.WindowEvent;
import java.awt.event.WindowListener;
import java.awt.event.WindowAdapter;
import java.awt.event.ActionListener;
import java.awt.event.ActionEvent;
public class FrameTest  //implements MouseListener
{
 static int xPoit;
 static int yPoit;
 static Graphics gp;
 static int num=1;
public static void main(String[] args)
{
Frame f=new Frame("实例窗口");
f.setSize(600,400);
f.setLocation(100,100);
f.setVisible(true);
gp=f.getGraphics();

f.setLayout(new FlowLayout());
Button bt1=new Button("中");
Button bt2=new Button("东");
Button bt3=new Button("西");
Button bt4=new Button("南");
Button bt5=new Button("北");
f.add(bt1,"Center");
myActionListener ml=new myActionListener();
bt1.addActionListener(ml);

f.add(bt2,"East");
f.add(bt3,"West");
f.add(bt4,"South");
f.add(bt5,"North");
bt2.addActionListener(ml);
bt3.addActionListener(ml);
bt4.addActionListener(ml);
bt5.addActionListener(ml);

//f.setBackground(Color.RED);

f.addMouseListener(new MouseAdapter()
{
public void mousePressed(MouseEvent emp)
{
xPoit=emp.getX();
yPoit=emp.getY();
}
 
 public void mouseReleased(MouseEvent emd)
 {
 
  gp.drawOval(xPoit,yPoit,emd.getX()-xPoit,emd.getY()-yPoit);
  System.out.println("画第"+FrameTest.num+"个圆");  
  FrameTest.num++;
 }
 
});

f.addWindowListener(new WindowAdapter()
{
public void windowClosing(WindowEvent e)
{
System.exit(0);
}

});


}}
class myActionListener implements ActionListener
{
Button gg;
public void actionPerformed(ActionEvent e)
{
gg=(Button)e.getSource();
//System.out.println(gg.getLabel());
//String str=e.getActionCommand();

if(gg.getLabel()=="中")
{
System.out.println("called program 1");

}
else
{
System.out.println("called program 2");

}

}
}

Answer 1

f.setVisible(true);这句的位置不对
修改后： 见红色字体import java.awt.Frame; 
import java.awt.Button; 
import java.awt.BorderLayout; 
import java.awt.Color; 
import java.applet.Applet; 
import java.awt.Graphics; 
import java.applet.Applet; 
import java.awt.FlowLayout; 
import java.awt.event.MouseAdapter; 
import java.awt.event.MouseEvent; 
import java.awt.event.WindowEvent; 
import java.awt.event.WindowListener; 
import java.awt.event.WindowAdapter; 
import java.awt.event.ActionListener; 
import java.awt.event.ActionEvent; 
public class FrameTest extends Frame  //implements MouseListener 
{ 
static int xPoit; 
static int yPoit; 
static Graphics gp; 
static int num=1; 
public static void main(String[] args) 
{ 
Frame f=new Frame("实例窗口"); 
f.setSize(600,400); 
f.setLocation(100,100); 
 
gp=f.getGraphics(); f.setLayout(new FlowLayout()); 
Button bt1=new Button("中"); 
Button bt2=new Button("东"); 
Button bt3=new Button("西"); 
Button bt4=new Button("南"); 
Button bt5=new Button("北"); 
f.add(bt1,"Center"); 
myActionListener ml=new myActionListener(); 
bt1.addActionListener(ml); f.add(bt2,"East"); 
f.add(bt3,"West"); 
f.add(bt4,"South"); 
f.add(bt5,"North"); 
f.setVisible(true);
bt2.addActionListener(ml); 
bt3.addActionListener(ml); 
bt4.addActionListener(ml); 
bt5.addActionListener(ml); //f.setBackground(Color.RED); f.addMouseListener(new MouseAdapter() 
{ 
public void mousePressed(MouseEvent emp) 
{ 
xPoit=emp.getX(); 
yPoit=emp.getY(); 
} public void mouseReleased(MouseEvent emd) 
{ gp.drawOval(xPoit,yPoit,emd.getX()-xPoit,emd.getY()-yPoit); 
System.out.println("画第"+FrameTest.num+"个圆");  
FrameTest.num++; 
} }); f.addWindowListener(new WindowAdapter() 
{ 
public void windowClosing(WindowEvent e) 
{ 
System.exit(0); 
} }); 
} } 
class myActionListener implements ActionListener 
{ 
Button gg; 
public void actionPerformed(ActionEvent e) 
{ 
gg=(Button)e.getSource(); 
//System.out.println(gg.getLabel()); 
//String str=e.getActionCommand(); if(gg.getLabel()=="中") 
{ 
System.out.println("called program 1"); } 
else 
{ 
System.out.println("called program 2"); } } 
} 
这样再试下吧

Answer 2

1楼兄弟，这样也不对，Button是出来了，可是鼠标拖动画图又报错了。

Answer 3

先解决楼主自己程序中的问题
f.setLayout(new FlowLayout()); 
和
f.add(bt1,"Center"); 
f.add(bt2,"East"); 
f.add(bt3,"West"); 
f.add(bt4,"South"); 
f.add(bt5,"North"); 
矛盾f.add(bt1,"Center"); 这种方式是BorderLayout中添加组件的方式，既然已经设置为FlowLayout，那就不能这样添加，f.add(bt1); 这样才对，五个都改了就好了。另外，强烈建议楼主使用swing包中的组件，还有注意编码规范，老三我改了一下楼主东东，如下
import java.awt.Container;
import java.awt.FlowLayout;
import java.awt.Graphics;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.UIManager;public class FrameTest extends JFrame implements ActionListener
{
    private static final long serialVersionUID = 3856883799347234725L;
    
    private Container contentPane;
    
    private JButton btnCenter;
    
    private JButton btnEast;
    
    private JButton btnWest;
    
    private JButton btnSouth;
    
    private JButton btnNorth;
    
    private Graphics g;
    
    private int x;    private int y;    private int num = 1;    public static void main(String[] args) throws Exception
    {
        UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
        new FrameTest();
    }
    
    public FrameTest()
    {
        contentPane = this.getContentPane();
        btnCenter = new JButton("中");
        btnEast = new JButton("东");
        btnWest = new JButton("西");
        btnSouth = new JButton("南");
        btnNorth = new JButton("北");
        
        this.setTitle("实例窗口");
        contentPane.setLayout(new FlowLayout());
        
        btnCenter.addActionListener(this);
        btnEast.addActionListener(this);
        btnWest.addActionListener(this);
        btnSouth.addActionListener(this);
        btnNorth.addActionListener(this);
        
        contentPane.add(btnCenter);
        contentPane.add(btnEast);
        contentPane.add(btnWest);
        contentPane.add(btnSouth);
        contentPane.add(btnNorth);
        
        contentPane.addMouseListener(new MouseAdapter()
        {
            public void mousePressed(MouseEvent e)
            {
                x = e.getX();
                y = e.getY();
            }            public void mouseReleased(MouseEvent e)
            {
                g.drawOval(x, y, e.getX() - x, e.getY() - y);
                System.out.println("画第" + num + "个圆");
                num++;
            }
        });
        
        this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        this.setSize(600, 400);
        this.setLocationRelativeTo(null);
        this.setVisible(true);
        g = contentPane.getGraphics();
    }
    
    public void actionPerformed(ActionEvent e)
    {
        JButton source = (JButton)e.getSource();        if(source.getText().equals("中"))
        {
            System.out.println("called program 1");
        }
        else
        {
            System.out.println("called program 2");
        }
    }
}

Answer 4

还有，楼主若要想真正意义上实现画圆的功能，以上的程序远远不够，你现在这个在调整窗口大小或者最小化后再显示出来（应该还有其他情况），那以前画的东东都没了，我上面改的也仅仅只是用swing包中的组件实现了楼主帖的程序中的功能而已，要想彻底解决问题，老三我帖上一个类似的供楼主参考（需要在JDK5及以上的环境中运行）
import java.awt.BasicStroke;
import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Cursor;
import java.awt.Font;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.event.ComponentAdapter;
import java.awt.event.ComponentEvent;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import java.awt.event.MouseMotionAdapter;
import java.util.ArrayList;
import java.util.List;import javax.swing.JComponent;
import javax.swing.JFrame;
import javax.swing.SwingUtilities;public class DrawPane extends JComponent
{
    private static final long serialVersionUID = -8963598853892068851L;    private int startX = 0;    private int startY = 0;    private int endX = 0;    private int endY = 0;    private List<Draw> drawList = new ArrayList<Draw>();    private Color color = Color.BLUE;    private Font font = new Font("Courier New", Font.BOLD, 14);    private boolean drawing = false;    public static void main(String[] args)
    {
        SwingUtilities.invokeLater(new Runnable()
        {
            public void run()
            {
                final DrawPane draw = new DrawPane();
                JFrame frame = new JFrame();
                frame.setTitle("Draw Demo");
                frame.add(draw, BorderLayout.CENTER);
                frame.setSize(500, 300);
                frame.setLocationRelativeTo(null);
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                frame.getContentPane().setBackground(Color.WHITE);
                frame.setVisible(true);
            }
        });
    }    public DrawPane()
    {
        super();
        init();
    }    public void paintComponent(Graphics g)
    {
        super.paintComponent(g);        for(Draw draw: drawList)
        {
            draw.draw(g);
        }        if(drawing)
        {
            g.drawString(endX + "," + endY, endX, endY);
            g.drawLine(startX, startY, endX, endY);
        }
    }    private void init()
    {
        addMouseListener(new MouseL());
        addMouseMotionListener(new MouseMotionL());
        addComponentListener(new ComponentL());
        setCursor(new Cursor(Cursor.CROSSHAIR_CURSOR));
    }    public Color getColor()
    {
        return color;
    }    public void setColor(Color color)
    {
        this.color = color;
    }    public Font getFont()
    {
        return font;
    }    public void setFont(Font font)
    {
        this.font = font;
    }    private class MouseL extends MouseAdapter
    {
        public void mousePressed(MouseEvent e)
        {
            startX = e.getX();
            startY = e.getY();
            drawList.add(new Text(font, color, startX, startY));
            repaint();
        }        public void mouseReleased(MouseEvent e)
        {
            drawing = false;
            endX = e.getX();
            endY = e.getY();
            drawList.add(new Line(font, color, startX, startY, endX, endY));
            drawList.add(new Text(font, color, endX, endY));
            repaint();
            startX = 0;
            startY = 0;
            endX = 0;
            endY = 0;
        }
    }    private class MouseMotionL extends MouseMotionAdapter
    {
        public void mouseDragged(final MouseEvent e)
        {
            drawing = true;
            endX = e.getX();
            endY = e.getY();
            repaint();
        }
    }    private class ComponentL extends ComponentAdapter
    {
        public void componentResized(final ComponentEvent e)
        {
            repaint();
        }
    }
    
    private class Line implements Draw
    {
        private int orgX = 0;        private int orgY = 0;        private int endX = 0;        private int endY = 0;        private Font font;        private Color color;        public Line(Font font, Color color, int orgX, int orgY, int endX, int endY)
        {
            this.orgX = orgX;
            this.orgY = orgY;
            this.endX = endX;
            this.endY = endY;
            this.color = color;
            this.font = font;
        }        public void draw(Graphics g)
        {
            g.setFont(font);
            g.setColor(color);
            g.drawLine(orgX, orgY, endX, endY);
        }
    }    private class Text implements Draw
    {
        private int orgX = 0;        private int orgY = 0;        private Font font;        private Color color;        public Text(Font font, Color color, int orgX, int orgY)
        {
            this.orgX = orgX;
            this.orgY = orgY;
            this.color = color;
            this.font = font;
        }        public void draw(Graphics g)
        {
            Graphics2D g2d = (Graphics2D)g;
            g2d.setStroke(new BasicStroke(2));
            g.setFont(font);
            g.setColor(color);
            g.drawString(orgX + "," + orgY, orgX, orgY);
        }
    }    private interface Draw
    {
        public void draw(Graphics g);
    }
}

Answer 5

3楼，4楼兄弟，我修改代码如下，但运行结果，还是和原来一样的
实际应用GUI的时候用Swing，我是想找出我这个用AWT写的怎么会出现这样的情况？？？import java.awt.Frame;
import java.awt.Button;
import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Graphics;
import java.awt.FlowLayout;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import java.awt.event.WindowEvent;
import java.awt.event.WindowListener;
import java.awt.event.WindowAdapter;
import java.awt.event.ActionListener;
import java.awt.event.ActionEvent;public class FrameTest  implements ActionListener
{
  private int xPoit;
  private int yPoit;
  private Graphics gp;
  private static int num=1;
  private Button bt1;
  private Button bt2;
  private Button bt3;
  private Button bt4;
  private Button bt5;
 
FrameTest()
{
Frame f=new Frame("实例窗口");
f.setSize(600,400);
f.setLocation(100,100);
f.setVisible(true);
gp=f.getGraphics();
f.setLayout(new FlowLayout());
  bt1=new Button("中");
  bt2=new Button("东");
  bt3=new Button("西");
  bt4=new Button("南");
  bt5=new Button("北");

f.add(bt1);
bt1.addActionListener(this);

f.add(bt2);
f.add(bt3);
f.add(bt4);
f.add(bt5);
bt2.addActionListener(this);
bt3.addActionListener(this);
bt5.addActionListener(this);

f.addMouseListener(new MouseAdapter()
{
public void mousePressed(MouseEvent emp)
{
xPoit=emp.getX();
yPoit=emp.getY();
}
 
 public void mouseReleased(MouseEvent emd)
 {
 
  gp.drawOval(xPoit,yPoit,emd.getX()-xPoit,emd.getY()-yPoit);
  System.out.println("画第"+FrameTest.num+"个圆");  
  FrameTest.num++;
 }
 
});

f.addWindowListener(new WindowAdapter()
{
public void windowClosing(WindowEvent e)
{
System.exit(0);
}

});
}


public static void main(String[] args)
{
FrameTest ft=new FrameTest();
}
 
public void actionPerformed(ActionEvent e)
{
Button gg=(Button)e.getSource();
if(gg.getLabel()=="中"){
System.out.println("called program 1");
}else{
System.out.println("called program 2");
}
}
}