怎么设置JTextField的maxLenght setFocus

Question

maxLengh自己写，setFocus直接调。

Answer 1

TO stonegump(龙飞虎) 
setFocus直接调,不知道怎么调用啊.

Answer 2

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;
            }
        }
    }
}