如何在JFram中添加JPanel?

Question

下面是小弟写的一段代码，想把JFrame分成5个格子，然后在上面三个格子里分别添加一个JPanel，JPanel中再添加按钮。
但是执行的时候提示下面的错误，这是怎么回事啊？
Exception in thread "main" java.lang.NullPointerException
at java.awt.Container.addImpl(Container.java:1015)
at java.awt.Container.add(Container.java:351)
at SeatClient.<init>(SeatClient.java:82)
at SeatClient.main(SeatClient.java:177)
import java.util.*;
import java.io.*;
import java.net.*;
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;public class SeatClient extends JFrame implements ActionListener {
    JPanel subPanel1 = new JPanel(new GridLayout(3,3));
    JPanel subPanel2 = new JPanel(new GridLayout(4,6));
    JPanel subPanel3 = new JPanel(new GridLayout(2,4));    JTextArea displayMessenger;    Button  allocateButton,
            button1A,
            button2A,
            button3A,
            button1B,
            button2B,
            button3B,
            button1C,
            button2C,
            button3C,            button4A,
            button5A,
            button6A,
            button7A,
            button4B,
            button5B,
            button6B,
            button7B,
            button4C,
            button5C,
            button6C,
            button7C,
            button4D,
            button5D,
            button6D,
            button7D,
            button4E,
            button5E,
            button6E,
            button7E,
            button4F,
            button5F,
            button6F,
            button7F,            button8A,
            button9A,
            button8B,
            button9B,
            button8C,
            button9C,
            button8D,
            button9D;    InputStream is=null;
    OutputStream os=null;
    PrintWriter pw=null;
    BufferedReader br=null;
    Socket s;    SeatClient(String title){
        super(title);
        setDefaultCloseOperation(EXIT_ON_CLOSE);        //set the grids of the frame as(5,1)
        getContentPane().setLayout(new GridLayout(5,1));            button1A=new Button("1A");
        subPanel1.add(button1A);
        button1B=new Button("1B");
        subPanel1.add(button1B);
        button1C=new Button("1C");
        subPanel1.add(button1C);
        getContentPane().add(subPanel1);        button2A=new Button("2A");
        subPanel1.add(button2C);
        button2B=new Button("2B");
        subPanel1.add(button2B);
        button2C=new Button("2C");
        subPanel1.add(button2C);
        button3A=new Button("3A");
        subPanel1.add(button3A);
        button3B=new Button("3B");
        subPanel1.add(button3B);
        button3C=new Button("3C");
        subPanel1.add(button3C);
        getContentPane().add(subPanel2);        //getContentPane().add(subPanel3);        displayMessenger = new JTextArea("Grey=free, click seat to reserve."+"\n\n"
                                        +"Green= reserved, click seat to free."+"\n\n"
                                        +"Red=allocated"+"\n");
        add(displayMessenger);        allocateButton = new Button("Allocate");
        add(allocateButton);        setSize(800,600);
        //pack();
        setVisible(true);
        button1A.addActionListener(this);
        button2A.addActionListener(this);
        button3A.addActionListener(this);
        button1B.addActionListener(this);
        button2B.addActionListener(this);
        button3B.addActionListener(this);
        button1C.addActionListener(this);
        button2C.addActionListener(this);
        button3C.addActionListener(this);        button4A.addActionListener(this);
        button4B.addActionListener(this);
        button4C.addActionListener(this);
        button4D.addActionListener(this);
        button4E.addActionListener(this);
        button4F.addActionListener(this);
        button5A.addActionListener(this);
        button5B.addActionListener(this);
        button5C.addActionListener(this);
        button5D.addActionListener(this);
        button5E.addActionListener(this);
        button5F.addActionListener(this);
        button6A.addActionListener(this);
        button6B.addActionListener(this);
        button6C.addActionListener(this);
        button6D.addActionListener(this);
        button6E.addActionListener(this);
        button6F.addActionListener(this);
        button7A.addActionListener(this);
        button7B.addActionListener(this);
        button7C.addActionListener(this);
        button7D.addActionListener(this);
        button7E.addActionListener(this);
        button7F.addActionListener(this);        button8A.addActionListener(this);
        button8B.addActionListener(this);
        button8C.addActionListener(this);
        button8D.addActionListener(this);
        button9A.addActionListener(this);
        button9B.addActionListener(this);
        button9C.addActionListener(this);
        button9D.addActionListener(this);
        try{
            s=new Socket("",2000);
            is=s.getInputStream();
            os=s.getOutputStream();            pw=new PrintWriter(os,true);
            br=new BufferedReader(new InputStreamReader(is));
        }
        catch(IOException e){
            System.out.println("Error connecting wth the Server "+e);
        }    }    public void actionPerformed(ActionEvent e){    }    public static void main(String[] args){
        //prompt user to enter name
        String name= JOptionPane.showInputDialog("What is your name?");        SeatClient c = new SeatClient(name);    }}

Answer 1

再问一句，如果要用AWT中的Frame，添加Panel，来完成这个界面应该怎么改变啊？

Answer 2

Frame fr=new Frame();
Panel pl=new Panel();
Button bt1=new Button();pl.add(btn1);
fr.add(pl,BorderLayout.SOUTH);
...

Answer 3

不好意思，能不能只用GridLayout，因为这是老师要求的：（

Answer 4

晕啊，楼主这么粗心的
这个地方的代码敲错了：
            button2A=new Button("2A");
            subPanel1.add(button2C);

Answer 5

看到那么多Button都晕了...

Answer 6

LZ定义那么多button却不实例化，运行出来一大堆Exception

Answer 7

下面是修改过的代码。在AWT的Frame添加的Panel:
import java.util.*;
import java.io.*;
import java.net.*;
import java.awt.*;
import java.awt.event.*;import javax.swing.*;
public class SeatClient extends Frame implements ActionListener { Panel subPanel1 = new Panel(new GridLayout(3,3));
    Panel subPanel2 = new Panel(new GridLayout(4,6));
    Panel subPanel3 = new Panel(new GridLayout(2,4));    JTextArea displayMessenger;    Button  allocateButton,
            button1A,
            button2A,
            button3A,
            button1B,
            button2B,
            button3B,
            button1C,
            button2C,
            button3C,            button4A,
            button5A,
            button6A,
            button7A,
            button4B,
            
            button4C,
            button5C;
            
    InputStream is=null;
    OutputStream os=null;
    PrintWriter pw=null;
    BufferedReader br=null;
    Socket s;    SeatClient(String title){
        super(title);
        this.addWindowListener(new WindowListener() {
         public void windowClosed(WindowEvent e) {
        
         } public void windowActivated(WindowEvent arg0) {
// TODO 自动生成方法存根

} public void windowClosing(WindowEvent arg0) {
System.exit(0);

} public void windowDeactivated(WindowEvent arg0) {
// TODO 自动生成方法存根

} public void windowDeiconified(WindowEvent arg0) {
// TODO 自动生成方法存根

} public void windowIconified(WindowEvent arg0) {
// TODO 自动生成方法存根

} public void windowOpened(WindowEvent arg0) {
// TODO 自动生成方法存根

}
        });        //set the grids of the frame as(5,1)
      setLayout(new GridLayout(5,1));            button1A=new Button("1A");
        subPanel1.add(button1A);
        button1B=new Button("1B");
        subPanel1.add(button1B);
        button1C=new Button("1C");
        subPanel1.add(button1C);
        add(subPanel1);        button2A=new Button("2A");
        subPanel1.add(button2A);
        button2B=new Button("2B");
        subPanel1.add(button2B);
        button2C=new Button("2C");
        subPanel1.add(button2C);
        button3A=new Button("3A");
        subPanel1.add(button3A);
        button3B=new Button("3B");
        subPanel1.add(button3B);
        button3C=new Button("3C");
        subPanel1.add(button3C);
       add(subPanel2);        //getContentPane().add(subPanel3);        displayMessenger = new JTextArea("Grey=free, click seat to reserve."+"\n\n"
                                        +"Green= reserved, click seat to free."+"\n\n"
                                        +"Red=allocated"+"\n");
        add(displayMessenger);        allocateButton = new Button("Allocate");
        add(allocateButton);        setSize(800,600);
        //pack();
        setVisible(true);
        button1A.addActionListener(this);
        button2A.addActionListener(this);
        button3A.addActionListener(this);
        button1B.addActionListener(this);
        button2B.addActionListener(this);
        button3B.addActionListener(this);
        button1C.addActionListener(this);
        button2C.addActionListener(this);
        button3C.addActionListener(this);        button4A = new Button("4A");
        button4A.addActionListener(this);
        button4B = new Button("4B");
        button4B.addActionListener(this);
        button4C = new Button("4C");
        button4C.addActionListener(this);
                try{
            s=new Socket("",2000);
            is=s.getInputStream();
            os=s.getOutputStream();            pw=new PrintWriter(os,true);
            br=new BufferedReader(new InputStreamReader(is));
        }
        catch(IOException e){
            System.out.println("Error connecting wth the Server "+e);
        }    }    public void actionPerformed(ActionEvent e){    }    public static void main(String[] args){
        //prompt user to enter name
        String name= JOptionPane.showInputDialog("What is your name?");        SeatClient c = new SeatClient(name);    }}

Answer 8

自动生成方法存根?能不能解释一下是什么意思啊？
自动生成方法存根 那几段代码是不是和下面的是一个原理？
 //dispose();By default, when the close button on a frame is clicked, nothing happens.
        //This shows how to properly close the application:
        addWindowListener(new WindowAdapter() {
        public void windowClosing(WindowEvent evt) {
            Frame frame = (Frame)evt.getSource();
            // Hide the frame
            frame.setVisible(false);
            // If the frame is no longer needed, call dispose
            frame.dispose();
        }
    });

Answer 9

Frame fr=new Frame();
Panel pl=new Panel();
Button bt1=new Button();pl.add(btn1);
fr.add(pl,BorderLayout.SOUTH);
...
--------------------------------
up

Answer 10

你把你定义Button改为数据,注册事件也用数组,那样会好些.
Button btn[]=new Button[100];
for(int i=0;i<100;i++)
{
     btn[i]=new Button(Intger.toString(i));
     btn[i].addActionListener(this);
}
其它的我没看,太长了,看了头痛...
觉得说得好,就给分哈..

Answer 11

JFrame jf=new JFrame();
Container cp =jf.getContentPane();
cp.add(new JPanel());
这样就行了

Answer 12

import javax.swing.*;
import java.awt.*;
public class Panel1 {
   public static void main(String[] args) {
   Panel1 gui = new Panel1();
   gui.go();
   }
   public void go() {
   JFrame frame = new  JFrame();
   JPanel panel = new JPanel(new GridLayout(2,2));
   panel.setBackground(Color.DARK_GRAY);
   
   panel.setLayout(new BoxLayout(panel,BoxLayout.Y_AXIS));
   
   JButton button = new JButton("yyc");
   JButton button1 = new JButton("chunyou128");
   
   panel.add(button);
   panel.add(button1);
   
   frame.getContentPane().add(BorderLayout.EAST,panel);
   frame.setSize(250,200);
   frame.setVisible(true);
   }
}

Answer 13

import org.eclipse.swt.SWT;
import org.eclipse.swt.layout.GridData;
import org.eclipse.swt.layout.GridLayout;
import org.eclipse.swt.widgets.Button;
import org.eclipse.swt.widgets.Display;
import org.eclipse.swt.widgets.Shell;/**//**
 * @author HexUzHoNG Created on 2005-6-23
 *
 */
public class GridLayoutDemo {    public static void main(String[] args) {
        
        Display display = new Display();
        Shell shell = new Shell(display);
        
        GridLayout gridLayout = new GridLayout();
        //设置为2列
        gridLayout.numColumns = 2;
        gridLayout.makeColumnsEqualWidth = true;
        shell.setLayout(gridLayout);
        
        GridData gd = new GridData(GridData.FILL_BOTH);
        Button butOne = new Button(shell, SWT.PUSH);
        butOne.setText("one");
        butOne.setLayoutData(gd);
        
        gd = new GridData(GridData.FILL_BOTH);
        Button butTwo = new Button(shell, SWT.PUSH);
        butTwo.setText("two");
        butTwo.setLayoutData(gd);
        
        gd = new GridData(GridData.FILL_BOTH);
        Button butThree = new Button(shell, SWT.PUSH);
        butThree.setText("three");
        butThree.setLayoutData(gd);
        
        gd = new GridData(GridData.FILL_BOTH);
        Button butFour = new Button(shell, SWT.PUSH);
        butFour.setText("four");
        butFour.setLayoutData(gd);
        
        shell.pack();
        shell.open();
        
        while (!shell.isDisposed()) {
            if (!display.readAndDispatch()) {
                display.sleep();
            }
        }
        
        display.dispose();
    }}