JTextField only digit

// Add feature to JTextField
// MyJTextField.java
import java.awt.event.KeyAdapter;
import java.awt.event.KeyEvent;
import javax.swing.JTextField;


public class MyJTextField extends JTextField {
 
   /** Creates a new instance of JOnlyDigitField */
   public MyJTextField() {      
       initFeature();
   }
  
   public MyJTextField(int width) {
       super(width);
       initFeature();
   }
 
   int length = 9; // real 10
   JTextField txfThis = this;
 
   public void setLength(int length) {
       this.length = length - 1;
   }
 
   public int getLength() {
       return length;
   }
 
   public void initFeature() {
       this.addKeyListener(new KeyAdapter() {
         
           public void keyTyped(KeyEvent e) {
             
               char c = e.getKeyChar(); 
   
               if ((!(Character.isDigit(c) 
                  || c == KeyEvent.VK_BACK_SPACE) 
                  || (c == KeyEvent.VK_DELETE))) {
                   e.consume();
               }    
          
               if (txfThis.getText().length() > length)
                   e.consume();
           }
       });
   }
 
}