Exception in thread "main" java.lang.NullPointerException，怎么老提示空指针错误呢？

显示全部楼层 · 2011-7-27 10:45:02

import javax.swing.*;
publicclass trycatch extends JFrame {

JPanel jp;

JLabel jb;

public trycatch(){

jb = new JLabel("呵呵",JLabel.CENTER);
jp.add(jb);
this.setSize(700, 500);
this.setLocation(200, 200);
this.setVisible(true);

}
public static void main(String args[]){

new trycatch();

}
}

千问 · 2011-7-27 10:45:02

import java.text.ParseException;import java.text.SimpleDateFormat;import java.util.Date;class Test2 { public static String getDate(){SimpleDateFormat ft = new SimpleDateFormat("yyyy/MM/dd");Date dd = new Date();return ft.format(dd); } public static long getQuot(String time1, String time2){long quot ...

千问 · 2011-7-27 10:45:02

Panel jp;只进行了声明，并没有实例化。jp.add(jb);之前增加jp = new JPanel();...

千问 · 2011-7-27 10:45:02

jp.add(jb);jp没有初始化！！！...