文本框事件

Question

文本框要求：
          要求该文本框只能输入数字，输入其他的报错并且弹出错误提示窗口。

Answer 1

import java.applet.*;
import java.awt.*;
import java.awt.event.*;
import javax.swing.JOptionPane;
public class Textfield extends Applet implements ActionListener
{
   TextField text1;
   public void init()
        {
           text1 = new TextField(20);
            add(new Label("输入数字: "));
            add(text1);
            text1.addActionListener(this);
        } 
    public void actionPerformed(ActionEvent e)
         {
            if(e.getSource() == text1)
                {
                    String isNum = text1.getText();
                     int len = isNum.length();
                    String n ="0123456789";
                    for(int i=0;i<len;i++)
                       {
                         try{
                               String loneNum = isNum.substring(i,i+1);
                               if( n.indexOf(loneNum) == -1)
                                   {
                                   JOptionPane.showMessageDialog(this,"非法字                                        符"," 警告对框",JOptionPane.WARNING_MESSAGE);
                                   text1.setText(null);
                                   break;
                                    }
                              }
                            catch(NumberFormatException ee)
                              {
                                 System.out.println(ee);
                              }
                       }
                }
         }
}

Answer 2

/**
*你应该监听键盘事件!!!
*/
import java.applet.*;
import java.awt.*;
import java.awt.event.*;
import javax.swing.JOptionPane;
public class Textfield extends Applet implements KeyListener
{
TextField text1;
public void init()
{
text1 = new TextField(20);
add(new Label("输入数字: "));
add(text1);
text1.addKeyListener(this);
}
public void keyPressed(KeyEvent e)
{
if("0123456789".indexOf(e.getKeyChar()+"")==-1)
{
JOptionPane.showMessageDialog(this,"非法字符"," 警告对框",JOptionPane.WARNING_MESSAGE);
text1.setText(null);return;
}
}
public void keyReleased(KeyEvent e)
{
if("0123456789".indexOf(e.getKeyChar()+"")==-1)
{
JOptionPane.showMessageDialog(this,"非法字符"," 警告对框",JOptionPane.WARNING_MESSAGE);
text1.setText(null);return;
}
}
public void keyTyped(KeyEvent e)
{}
}