這是控制臺的所顯示的結果：
Exception?in?thread?"main"?java.lang.NullPointerException
at?com.zyn_1.WriteNote.myEvent(WriteNote.java:36)
at?com.zyn_1.WriteNote.init(WriteNote.java:30)
at?com.zyn_1.WriteNote.<init>(WriteNote.java:14)
at?com.zyn_1.WriteNote.main(WriteNote.java:46)
這是源代碼：package?com.zyn_1;
import?java.awt.*;
import?java.awt.event.*;
public?class?WriteNote?{
private?Frame?f;
private?MenuBar?mb;
private?Menu?m;
private?MenuItem?mi;
WriteNote(){
init();
}
public?void?init(){
Frame?f?=?new?Frame("記事本");//創建frame窗體
//對窗體進行基本設置
f.setLayout(new?FlowLayout());//設置布局
f.setLocation(300,?100);//位置
f.setSize(500,600); //大小
mb?=?new?MenuBar();
m?=?new?Menu("文件");
mi?=?new?MenuItem("退出");
mb.add(m);
m.add(mi);
myEvent();
f.setMenuBar(mb);
f.setVisible(true);//通過setvisiable（true）顯示窗體
}
public?void?myEvent(){
f.addWindowListener(new?WindowAdapter()?{
public??void?windowClosing(WindowEvent?e){
System.exit(0);
}
});
}
public?static?void?main(String[]?args)?{
//?TODO?Auto-generated?method?stub
new?WriteNote();
}
}
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