画面合并的问题

Question

我写了一个差不多的，没出这个问题啊
import java.awt.*;
import javax.swing.*;public class Test
{
public static void main(String[] args)
{
JFrame2 jf2 = new JFrame2();
jf2.setSize(300,300);
jf2.setVisible(true);
}
}
class JFrame1 extends JFrame
{
Container con;
JButton jb1;
public JFrame1()
{
 con = this.getContentPane();
 con.setLayout(new FlowLayout());
 jb1 = new JButton("Button1");
 con.add(jb1);
}
}
class JFrame2 extends JFrame1
{
JButton jb2;
public JFrame2()
{
con = this.getContentPane();
jb2 = new JButton("Button2");
con.add(jb2);
}
}
楼主最好把源代码贴出来，看看是不是因为加的组件只声明而忘记构造了。

Answer 1

NullPointerException一般是没初始化

Answer 2

晕，写super()干吗？
你每次自己写窗体继承了JFrame的时候，构造函数里写super()么？

Answer 3

他是直接继承JFrame吗？如果不是很有可能是自己的一些对象没有初始化。

Answer 4

先谢谢大家,问题找到了,是因为JFrame１的init()和JFrame2的init()重名了.大家还要帮我一个忙,我的排版不太对,不知道为什么,大家帮看一下:
package FrameNoTitle;import java.awt.*;
import javax.swing.*;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import java.awt.Point;
import java.awt.event.MouseMotionAdapter;
import java.awt.Toolkit;
import java.awt.Dimension;public class FrameNoTitle extends JFrame
{
    javax.swing.JLabel lblUserId = new javax.swing.JLabel();
    javax.swing.JLabel lblSystemTime = new javax.swing.JLabel();
    javax.swing.JLabel lblTitle = new javax.swing.JLabel();
    int iWindowWidth;
    int iWindowHeight;    private Point pressedPt;    public FrameNoTitle()
    {
        setDefaultCloseOperation(EXIT_ON_CLOSE);
        this.setSize(400, 300);
        this.setUndecorated(true);
        this.addMouseListener(new MouseAdapter() {
            public void mousePressed(MouseEvent e) {
                pressedPt = e.getPoint();
            }
        });        this.addMouseMotionListener(new MouseMotionAdapter() {
            public void mouseDragged(MouseEvent e) {
                JFrame frame = (JFrame) e.getSource();
                Point location = frame.getLocation();
                int x = e.getX() - pressedPt.x + location.x;
                int y = e.getY() - pressedPt.y + location.y;
                frame.setLocation(x, y);
            }
        });        Dimension screenSize = Toolkit.getDefaultToolkit().getScreenSize();
        Dimension frameSize = this.getSize();
        this.setLocation((screenSize.width - frameSize.width)/2, (screenSize.height - frameSize.height)/2);        initFrame();
        }    public void initFrame()
    {
        GridBagConstraints gridBagConstraints = new GridBagConstraints();
        int anchor = gridBagConstraints.CENTER;
        int iFill = gridBagConstraints.NONE;        getContentPane().setLayout(new GridBagLayout());
        setSize(iWindowWidth, iWindowHeight);        lblUserId.setHorizontalAlignment(javax.swing.SwingConstants.RIGHT);
        lblUserId.setFont(new Font("Serif", Font.PLAIN, 12));
        lblUserId.setText("20030901");
        getContentPane().add(lblUserId,new GridBagConstraints(1,0,1,1,0.0,0.0,anchor,iFill,new Insets(0,12,0,10),60,9));        lblTitle.setHorizontalAlignment(javax.swing.SwingConstants.CENTER);
        lblTitle.setFont(new Font("Serif", Font.PLAIN, 18));
        getContentPane().add(lblTitle,new GridBagConstraints(0,1,1,2,0.0,0.0,anchor,iFill,new Insets(12,108,206,0),44,2));        lblSystemTime.setHorizontalAlignment(javax.swing.SwingConstants.RIGHT);
        lblSystemTime.setFont(new Font("Serif", Font.PLAIN, 12));
        lblSystemTime.setText("2003/09/01 12:01:20");
        getContentPane().add(lblSystemTime,new GridBagConstraints(1,1,1,1,0.0,0.0,anchor,iFill,new Insets(0,12,0,10),3,9));
    }    public void setTitle(String sTitle)
    {
        lblTitle.setText("《" + sTitle + "》");
    }    public void setWindowWidth(int iWindowWidth)
    {
        this.iWindowWidth = iWindowWidth;
    }    public void setWindowHeight(int iWindowHeight)
    {
        this.iWindowHeight = iWindowHeight;
    }    public static void main(String[] args)
    {
        FrameNoTitle app = new FrameNoTitle();
        app.setWindowWidth(426);
        app.setWindowHeight(266);
        app.setTitle("标            题");
        app.show();
    }
}--------------------------------------------------------------
package GUI;import java.awt.*;
import javax.swing.*;
import FrameNoTitle.*;public class Form2 extends FrameNoTitle
{
    public Form2()
    {
        init();
    }    public static void main(String[] args)
    {
        Form2 app = new Form2();
        app.setSize(337,380);
        app.setTitle("标题");
        app.show();
    }    public void init()
    {
        GridBagConstraints gridBagConstraints = new GridBagConstraints();
        int anchor = gridBagConstraints.CENTER;
        int iFill = gridBagConstraints.NONE;
        int iLine = 3;        getContentPane().setLayout(new GridBagLayout());
        getContentPane().setFont(new Font("Dialog", Font.PLAIN, 12));        lbl.setText("lbl：");
        getContentPane().add(lbl,new GridBagConstraints(0,iLine,1,1,0.0,0.0,anchor,iFill,new Insets(24,36,0,0),72,8));
        lbl.setFont(new Font("Serif", Font.PLAIN, 12));
        getContentPane().add(txt,new GridBagConstraints(1,iLine,2,1,0.0,0.0,anchor,iFill,new Insets(12,0,0,0),156,4));
        txt.setFont(new Font("Serif", Font.PLAIN, 12));
        iLine = iLine + 1;    
    }
    javax.swing.JLabel lbl = new javax.swing.JLabel();
    javax.swing.JTextField txt = new javax.swing.JTextField();
    
}

Answer 5

是父窗体与子窗体不在同一个Container中引起的.

Answer 6

package TextBox;import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
import java.lang.*;
import java.awt.event.KeyEvent;
import java.awt.event.KeyListener;
import javax.swing.text.AttributeSet;
import javax.swing.text.BadLocationException;
import javax.swing.text.Document;
import javax.swing.text.PlainDocument;
import TextBox.*;public class TextBox extends JTextField
{
    private int iMaxLen;    public TextBox()
    {
        super();
        LoadEvent();
    }    public void setMaxLength(int iMaxLength)
    {
        iMaxLen = iMaxLength;
    }
    public void LoadEvent()
    {
        this.addFocusListener(new FocusListener(){
            public void focusLost(FocusEvent e)
            {
                LostFocus();
            }
            public void focusGained(FocusEvent e)
            {
                GetFocus();
            }
        });        this.addKeyListener(new MaxLengthKeyListener());
    }
    public void LostFocus()
    {
        if(!IsNumber(this.getText()))
        {
            this.requestFocus();
        }
    }    public void GetFocus()
    {
        this.selectAll();
    }    public static  boolean IsNumber(String  sTmp)
    {
        String sNumber[]={"0","1","2","3","4","5","6","7","8","9"};
        String sComp="";        for(int j=0;j<sTmp.length();j++ )
        {
            sComp=sTmp.substring(j,j+1);
            for(int i=0;i <10 ;i++ )
            {
                if( sComp.equals(sNumber[i]) )
                {
                    break;
                }
                if ( i == 9)
                {
                    return false;
                }
            }
        }
        return true;
    }    protected Document createDefaultModel()
    {
        return new MaxLengthDocument();
    }    class MaxLengthDocument extends PlainDocument
    {
        private int added = 0;        public void insertString(int arg0, String arg1, AttributeSet arg2) throws BadLocationException
        {
            if (arg0 < iMaxLen)
            {
                super.insertString(arg0, arg1, arg2);
            }
        }
    }    class MaxLengthKeyListener implements KeyListener
    {
        private String oldString;        public void keyPressed(KeyEvent arg0)
        {
            checkMaxLength();
        }        public void keyReleased(KeyEvent arg0)
        {
            checkMaxLength();
        }        public void keyTyped(KeyEvent arg0)
        {
            checkMaxLength();
        }        private void checkMaxLength()
        {
            String checkString = getText();
            byte[] byteLength = checkString.getBytes();
            if (byteLength.length > iMaxLen)
            {
                setText(oldString);
            } else {
                oldString = checkString;
            }
        }
    }
}