import java.awt.*;
import java.awt.event.*;
public class j1216_4 extends Frame{
private Frame frm;
public Button btn;
public BorderLayout layout;
public Graphics g;
public void initial(){
frm=new Frame("My first AWT program!!");
btn=new Button("Draw!!");
layout=new BorderLayout();
g=getGraphics();
frm.setLayout(layout);
frm.setTitle("按鈕事件");
frm.setSize(200,150);
frm.add(btn,layout.SOUTH);
btn.addActionListener(new ActionListener(){
public void actionPerformed(ActionEvent e){
g.drawRect(100,50,70,55);
}
});
frm.setVisible(true);
frm.addWindowListener(new WindowAdapter(){
public void windowClosing(WindowEvent e){System.exit(0);}
});
}
public static void main(String []args){
j1216_4 myFrame=new j1216_4();
myFrame.initial();
}
}
以上是程式碼,可是好像被拋出例外跑不出結果
Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
at j1216_4$1.actionPerformed(j1216_4.java:31)
at java.awt.Button.processActionEvent(Button.java:409)
at java.awt.Button.processEvent(Button.java:377)
請問要怎麼改才可以跑呢@@?
到底哪裏出問題~~
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※ 編輯: supercygnus 來自: 220.132.37.216 (12/16 14:45)