Pass a method as an object to DocumentListener

Question

So far, I have been assigning document listeners to JTextfields within the same class as the JTextField, as in...
               private createJTextField(){
                   JTextField t = new JTextField();
                   t.getDocument().addDocumentListener(documentListener());
               private DocumentListener documentListener() {
              DocumentListener listener = new DocumentListener(){
                  public void changedUpdate(DocumentEvent e){textFieldActions();}
              public void removeUpdate(DocumentEvent e){textFieldActions();}
                     public void insertUpdate(DocumentEvent e){textFieldActions();};};
             return listener;
            private void textFieldActions() {
              //Do something, like search the text in the JTextField for a string;
              }This does work, but it means I have to include similar blocks of code for every JTextField I create.
...so, I thought it would be better to set up a utility that I could pass the JTextField and method to, which would assign the method to the DocumentListener. Something like...
     private JTextField t;
     private Boolean b;
     private JTextFieldDocumentListenerUtility l;
     protected void setUp(){
          t = new JTextField();
          b = false;
          l = new JTextFieldDocumentListenerUtility();
     public void testDocumentListener(){
          assertFalse(b);
          l.assignAction(t, someAction());
          t.setText("bogus");
          assertTrue(b);
     private void someAction() {
          b = true;
               }The JTextFieldDocumentListenerUtility class includes the "private DocumentListener documentListener()" method in the first block of code.
However, I can't pass the method "as is". I think (and I need some guidance here) its because the method "someAction()" returns a void, whereas I need to pass an object to the JTextFieldDocumentListenerUtility.
What is the tidiest way to do this, given that I'm trying to cut down duplicate code every time I create a JTextField?
Can someone please walk me through this?

Answer 1

You could use the Strategy pattern.
Basically creating a DocumentListener implementation that accepts as parameters the JTextField and a separate "Operation" instance. Where operation would be an
interface that would define a single operation() method (or 3 different operation methods if you want different operations performed for the changed/remove/insert events).
Some non-tested sample code.
public class MyListener implements DocumentListener {
    private JTextField field;
    private Operation operation;
    public MyListener(JTextField field, Operation operation) {
        this.field = field;
        this.operation = operation;
    public void changedUpdate(DocumentEvent e) { operation.changed(field); }
    public void removeUpdate(DocumentEvent e) { operation.remove(field); }
    public void insertUpdate(DocumentEvent e) { operation.insert(field); }
}This way if you have 10 textfields that need to behave in a similar way, you'd need only create 1 Operation implementation that handles the functionality and just use
t.getDocument().addDocumentListener(new MyListener(t, new MyStandardOperation()));Since you can't pass around only methods, you need to have a class to contain them in.
But if you need to have several textfields that have similar functionality, you'll have the functionality contained in a single place and cut down on the boilerplate code.