高手帮我看看下面的程序哪里出了问题!高分!

Question

container.setLayout(grid2);有问题，但不知怎么改，

Answer 1

运行时有空指针异常，需要加上一句container=new Container();但是为什么layout没改变我也不知道。但是container.setLayout(grid2);和container.setLayout(grid1);确实是执行了。

Answer 2

too easy,改成这样就没问题了import java.awt.*;
import java.awt.event.*;
import javax.swing.*;public class GridLayoutDemo
    extends JFrame
    implements ActionListener {
    private JButton buttons[];
    private final String names[] = {
        "one", "two", "three", "four", "five", "six"};
    private boolean flag = true;
    private Container container;
    private GridLayout grid1, grid2;    public GridLayoutDemo() {
        super("GridLayout Demo");
        grid1 = new GridLayout(2, 3, 5, 5);
        grid2 = new GridLayout(3, 2);        container = getContentPane();
        container.setLayout(grid1);        buttons = new JButton[names.length];        for (int count = 0; count < names.length; count++) {
            buttons[count] = new JButton(names[count]);
            buttons[count].addActionListener(this);
            container.add(buttons[count]);
        }
        this.setSize(300, 150);
        this.setVisible(true);
    }    public void actionPerformed(ActionEvent e) {
        if (flag)
            container.setLayout(grid2);
        else
            container.setLayout(grid1);        flag = !flag;
        container.validate();
    }    public static void main(String agrs[]) {
        GridLayoutDemo application = new GridLayoutDemo();
        application.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    }

Answer 3

原因:构造函数里container是局部变量,而actionPerformed方法里container是全局变量.解决办法我在楼上给出了,楼主结贴给分吧.