[Java]控制JTextField的輸入為數字

  import   javax.swing.text.*;  
  import   java.awt.*;  
  /**  
    *   描述：使用格式JTextField.setDocument(new NumberDocument())即可  
    **/  
  public class NumberDocument extends PlainDocument   {  
      public void insertString(int offs, String str, AttributeSet   a)  
      throws BadLocationException {  
          char[] source = str.toCharArray();  
          char[] result = new   char[source.length];  
          int j =   0;  
          for (int i = 0; i < result.length; i++){
              if( Character.isDigit(source[i]) )  //是數字  
                  result[j++]  = source[i];  
              else{                               //不是數字  
                  Toolkit.getDefaultToolkit().beep();  
                  System.out.println("你輸入了非數字字符！！")  
              }  
          }
          super.insertString(offs,new String(result,0,j),a);  
      }  
  }