当前页面: 开发资料首页 → J2SE 专题 → NullPointerException问题

NullPointerException问题

摘要: NullPointerException问题

编译没有问题
运行是出现以下错误
Exception in thread "main" java.lang.NullPointerException
at GameButton.main(GameButton.java:36)

---

源程序代码如下：

import javax.swing.*;
import java.awt.GridLayout;
public class GameButton extends JButton {
private int X;
privateint Y;
private int value;
private boolean selected;
private static GameButton[][] gbGroup;

public GameButton(){
super();
}

public GameButton(String s){
super(s);
}


public void setX(int x){X=x;}
public void setY(int y){Y=y;}
public void setValue(int V){value=V;}
public int getX(){return X;}
public int getY(){return Y;}
public int getValue(){return value;}
public void erase(){setValue(0);}


public static void main(String[] args) {
JFrame mFrame=new JFrame("lianPanel");
mFrame.setSize(600,400);
mFrame.setLocation(100,100);
JPanel panel=new JPanel(new GridLayout(3,3));

for(int a=0;a<3;a++){
for(int b=0;b<3;b++){
gbGroup[a][b]=new GameButton(a+b+"");//出问题的是这一行
}
}

for(int i=0;i<3;i++){
for(int j=0;j<3;j++)
panel.add(gbGroup[i][j]);
}
mFrame.add(panel,"Center");
mFrame.setVisible(true);
}
}

---

import javax.swing.*;
import java.awt.GridLayout;
public class GameButton extends JButton {
private int X;
privateint Y;
private int value;
private boolean selected;
private static GameButton[][] gbGroup = new GameButton[3][3] ; //修改这里就OK

public GameButton(){
super();
}

public GameButton(String s){
super(s);
}


public void setX(int x){X=x;}
public void setY(int y){Y=y;}
public void setValue(int V){value=V;}
public int getX(){return X;}
public int getY(){return Y;}
public int getValue(){return value;}
public void erase(){setValue(0);}


public static void main(String[] args) {
JFrame mFrame=new JFrame("lianPanel");
mFrame.setSize(600,400);
mFrame.setLocation(100,100);
JPanel panel=new JPanel(new GridLayout(3,3));

for(int a=0;a<3;a++){
for(int b=0;b<3;b++){
gbGroup[a][b]=new GameButton(a+b+"");//出问题的是这一行
}
}

for(int i=0;i<3;i++){
for(int j=0;j<3;j++)
panel.add(gbGroup[i][j]);
}
mFrame.add(panel,"Center");
mFrame.setVisible(true);
}
}

---

多谢碧海夜心！
到这里又有一个问题，为什么这些Button要我把鼠标放上去才显示出来啊？
我的程序是想要它自动全部显示出来的阿

---

空指针异常

---