Re: Problem with JavaFX ChangeListener?

I'm trying to teach myself JavaFX and have hit a snag. In the program
below I add a ChangeListener to a TextField. The Java8 method works
fine, adding an anonymous ChangeListener class works fine but I can't
create a class that implements ChangeListener and get it to compile.

         class LengthListener<String> implements ChangeListener<String> {

             private final int length;

             public LengthListener(int length) {
                 this.length = length;
             }

             @Override public void changed(
              ObservableValue<? extends String> observable,
              String oldValue,String newValue) {
                 if (newValue.length() > length)
                     ((StringProperty)observable).setValue(
                      newValue.substring(0,length));
             }
         }
         textField.textProperty().addListener(new LengthListener(4));