java不知错误原因？

[hh81658388]

我写了个鼠标画图的程序，能通过编译，但运行出错，不知是什么原因，希望高手指点！兄弟我先谢了！
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.awt.Container;
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;
public class FrameTest //implements MouseListener
{
static int xPoit;
static int yPoit;

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);
f.addMouseListener(new MouseAdapter()
{
public void mousePressed(MouseEvent emp)
{
xPoit=emp.getX();
yPoit=emp.getY();
System.out.println("按下");
}

public void mouseReleased(MouseEvent e)
{
Container app=new Container();
Graphics g=app.getGraphics();
System.out.println("拖动显示1");
g.drawOval(xPoit,yPoit,e.getX()-xPoit,e.getY()-yPoit);
System.out.println("拖动显示2");
}
});

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

});

}

}

[aqiansunboy]

import java.awt.Frame;
import java.awt.Graphics;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import java.awt.event.MouseListener;
import java.awt.event.WindowEvent;
import java.awt.event.WindowAdapter;

public class FrameTest extends Frame// implements MouseListener
{
static int xPoit;

static int yPoit;

static Graphics g;

public FrameTest() {

Frame f = new Frame("实例窗口");
f.setSize(600, 400);
f.setLocation(100, 100);
f.setVisible(true);

g = f.getGraphics();

MouseAdapter1 adapter = new MouseAdapter1();
f.addMouseListener(adapter);
}

public static void main(String[] args) {

new FrameTest();

}

class MouseAdapter1 extends MouseAdapter {
public void mousePressed(MouseEvent emp) {
xPoit = emp.getX();
yPoit = emp.getY();
System.out.println("按下");
}

public void mouseReleased(MouseEvent e) {
System.out.println("拖动显示1");
g.drawOval(xPoit, yPoit, e.getX() - xPoit, e.getY() - yPoit);
System.out.println("拖动显示2");
}
}

}

[hh81658388]

谢谢楼上兄弟！

[hh81658388]

请教3楼兄，按照原来代码的结构，错误在哪里呢？
先谢了！

[hh81658388]

我测试了一下，错误发生在
g.drawOval(xPoit, yPoit, e.getX() - xPoit, e.getY() - yPoit); 这句，
真搞不明白，这句怎么错了呢？这个方法中的各个参数都有值的，可以输出来啊，不好意思啊，本人刚学习，让大家见笑！
下面的那句没有执行。

[hh81658388]

错误找到了！谢了，各位，
Graphics 引用不对，

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.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import java.awt.event.WindowEvent;
import java.awt.event.WindowListener;
import java.awt.event.WindowAdapter;

public class FrameTest //implements MouseListener
{
static int xPoit;
static int yPoit;
static Graphics gh;
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);
gh=f.getGraphics();
f.addMouseListener(new MouseAdapter()
{
public void mousePressed(MouseEvent emp)
{
xPoit=emp.getX();
yPoit=emp.getY();
System.out.println("按下");
}

public void mouseReleased(MouseEvent e)
{

System.out.println("拖动显示1");
gh.drawOval(xPoit,yPoit,e.getX()-xPoit,e.getY()-yPoit);
System.out.println("拖动显示2");
}
});

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

});

}

}

[wxzyydy]

错误太多了，不想查了

[yangfeitarena]

代码要放在代码区，这么写一点格式没有，看得太费劲，没谁愿意给你分析

[fanyuanwaifdl]

Graphics 引用不对， 

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.awt.event.MouseAdapter; 
import java.awt.event.MouseEvent; 
import java.awt.event.WindowEvent; 
import java.awt.event.WindowListener; 
import java.awt.event.WindowAdapter; 

public class FrameTest  //implements MouseListener 
{ 
static int xPoit; 
static int yPoit; 
static Graphics gh; 
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); 
gh=f.getGraphics(); 
f.addMouseListener(new MouseAdapter() 
{ 
public void mousePressed(MouseEvent emp) 
{ 
xPoit=emp.getX(); 
yPoit=emp.getY(); 
System.out.println("按下"); 
} 

public void mouseReleased(MouseEvent e) 
{ 

System.out.println("拖动显示1");  
gh.drawOval(xPoit,yPoit,e.getX()-xPoit,e.getY()-yPoit); 
          System.out.println("拖动显示2");      
} 
}); 

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

}); 

} 

}