郁闷死了！为什么不能这样初始化按钮！

[飞行的兔子]

import javax.swing.JApplet;
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;

/*
* Created on 2004-9-8
*
* To change the template for this generated file go to
* Window>Preferences>Java>Code Generation>Code and Comments
*/

/**
* @author Administrator
*
* To change the template for this generated type comment go to
* Window>Preferences>Java>Code Generation>Code and Comments
*/
public class Calculator extends JApplet {
JPanel p1,p2;
JButton Calkey[];
JTextArea result;
JLabel show;
String[] Signs={"1","2","3","4","5","6","7","8","9","0","/","*","-","+",".","sqrt","%","1/x","="};
String S="";

public Calculator(){

setSize(400,300);
show();

}
public void init(){

p1=new JPanel();
show=new JLabel("result:");
result=new JTextArea(1,15);
p1.add(show);
p1.add(result);
p2=new JPanel();
p2.setLayout(new GridLayout(4,5));

Container c=getContentPane();
c.setLayout(new BorderLayout());
for(int i=0;i<Signs.length;i++){
Calkey[i]=new JButton(Signs[i]);//程序总是报告这行有空指针异常
p2.add(Calkey[i]);
}
c.add(BorderLayout.NORTH,p1);
c.add(BorderLayout.SOUTH,p2);
}


}
为什么有这样的错误呢？？？我觉得没问题啊！

[andy_zhang_ping]

JButton Calkey；声明

for(int i=0;i<Signs.length;i++){
Calkey=new JButton(Signs[i]);
你有for语句就不要用数组有标识按扭，你试试

[飞行的兔子]

我想问一下，为什么不能用字符窜数组标识按钮数组呢？？谢谢！

[oicqren]

开始声明了
JButton Calkey[];
后面你又用了Calkey[i],应该是Calkey[]数组没被初始化的缘故吧！
至少应该先分配一个长度；
例如：
JButton Calkey[Signs.length]

[wandou999]

一楼说的对

[fuzhe]

字符串数组可以标志按钮数组，前提是字符串数组里面必须有字符串成员，你的CalKey数组根本没有初始化，拿什么来标志按钮对象呢？所以肯定有空指针错误

[射天狼]

JButton[] Calkey = new JButton [20];
//这样声明就可以了~~~~