程序如下：
package?com.zyn_1;
import?java.awt.*;
import?java.awt.event.*;
public?class?WriteNote?{
private?Frame?f;
private?MenuBar?mb;
private?Menu?m1,m2;
private?MenuItem?mi1,mi2,mi3,mi4,mi5,mi6;
private?FileDialog?open,save;
private?TextArea?ta;
WriteNote(){
init();
}
public?void?init(){
?f?=?new?Frame("記事本");//創(chuàng)建frame窗體
//對窗體進行基本設置
f.setLayout(new?FlowLayout());//設置布局
f.setLocation(300,?70);//位置
f.setSize(600,640); //大小
m1?=?new?Menu?("文件");
m2?=?new?Menu("幫助");
mi1?=?new?MenuItem("新建");
mi2?=?new?MenuItem("打開");
mi3?=?new?MenuItem("保存");
mi4?=?new?MenuItem("另存為");
mi5?=?new?MenuItem("退出");
mi6?=?new?MenuItem("版本");
mb.add(m1);
mb.add(m2);
m1.add(mi1);
m1.add(mi2);
m1.add(mi3);
m1.add(mi4);
m1.add(mi5);
m2.add(mi6);
open?=?new?FileDialog(f,"打開",FileDialog.LOAD);
save?=?new?FileDialog(f,"保存",FileDialog.SAVE);
ta?=?new?TextArea();
f.add(ta);
myEvent();
f.setMenuBar(mb);
f.setVisible(true);//通過setvisiable（true）顯示窗體
}
public?void?myEvent(){
mi2.addActionListener(new?ActionListener()?{
@Override
public?void?actionPerformed(ActionEvent?e)?{
//?TODO?Auto-generated?method?stub
open.setVisible(true);
}
});
mi5.addActionListener(new?ActionListener()?{
@Override
public?void?actionPerformed(ActionEvent?e)?{
//?TODO?Auto-generated?method?stub
System.exit(0);
}
});
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();
}
}
控制臺顯示內(nèi)容：
Exception?in?thread?"main"?java.lang.NullPointerException
at?com.zyn_1.WriteNote.init(WriteNote.java:32)
at?com.zyn_1.WriteNote.<init>(WriteNote.java:15)
at?com.zyn_1.WriteNote.main(WriteNote.java:78)
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