Question

JAVA CardLayout布局问题

JAVA，新建了一个窗体，用了一个循环在窗体中添加了4个JPanel,又用了一个循环在JPanel上添加了4个按钮，用CardLayout布局，给按钮添加事件，当单击按钮时显示下一个JPanel，但最后一行代码不知怎么改，无法实现预期效果，求解！

import java.awt.Frame;
import java.awt.CardLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;

public class CardLayoutUse extends JFrame implements ActionListener{
private JPanel p;
private CardLayout cl;

public CardLayoutUse(){
CardLayout cl = new CardLayout();
setLayout(cl);

JPanel p[] = new JPanel[4];
for(int i = 0; i < 4; i++){
p[i] = new JPanel();
add(p [i],p[i]);
}

JButton b[] = new JButton[4];
for(int i = 0; i < 4; i++){
int a = i + 1;
b[i] = new JButton("第" + a + "页,下一页");
b[i].addActionListener(this);
p[i].add(b[i]);
}

setVisible(true);
setBounds(300, 300, 300, 300);
}

public static void main(String[] args) {
new CardLayoutUse();

}

@Override
public void actionPerformed(ActionEvent arg0) {
for(int i = 0; i < 4; i++){
cl.show(this,p[i]);
}
}
}

Answer 1

你的程序我帮你改了一下，现在运行没问题了，你看看吧。
import java.awt.CardLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;

public class CardLayoutUse extends JFrame implements ActionListener{
private JPanel p1;
private CardLayout cl;
private int j=1;
public CardLayoutUse(){
p1=new JPanel();
cl = new CardLayout();
p1.setLayout(cl);

JPanel p[] = new JPanel[4];
for(int i = 0; i < 4; i++){
p[i] = new JPanel();
p1.add(p[i],String.valueOf(i));
}

JButton b[] = new JButton[4];
for(int i = 0; i < 4; i++){
int a = i + 1;
b[i] = new JButton("第" + a + "页,下一页");
b[i].addActionListener(this);
p[i].add(b[i]);
}

add(p1);
setVisible(true);
setBounds(300, 300, 300, 300);
}

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

public void actionPerformed(ActionEvent arg0) {
cl.show(p1,String.valueOf(j++));
if(j==4) j=0;
}
}

Answer 2

同求！

Answer 3

NullPointerException!
看下这个有用没：
JButton jb = (JButton)e.getSource();
JPanel pel = (JPanel)jb.getParent();

Answer 4

main语句，好像不是这样的吧