java applet 源程序学习1

- Limit TextField input to a maximum length
import java.awt.*;
import java.awt.event.*;
public class TextFieldWithLimit extends TextField
    implements KeyListener {
    private int  maxLength;
    public TextFieldWithLimit
           (String initialStr,int col,int maxLength) {
      super(initialStr,col);
      this.maxLength = maxLength;
      addKeyListener(this);
      }
    public TextFieldWithLimit (int col,int maxLength) {
      this("",col,maxLength);
      }
    public void keyTyped(KeyEvent e) {
      char c = e.getKeyChar();
      int len = getText().length();
      if (len < maxLength) {
         return;
         }
      else {
         if((c==KeyEvent.VK_BACK_SPACE)||
            (c==KeyEvent.VK_DELETE) ||
            (c==KeyEvent.VK_ENTER)||
            (c==KeyEvent.VK_TAB)||
             e.isActionKey())
            return;
          else {
            e.consume();
           }
          }
      }
    public void keyPressed(KeyEvent e) { }
    public void keyReleased(KeyEvent e) { }
    }