Add listener to ArrayList

Question

I have an ArrayList which I add some Objects to it dynamically, and I have a JButton. The ArrayList is empty when running my program and the JButton is set to setEnabled(fal

Answer 1

Following SimpleIntegerProperty syntax I made an ArrayList which fire when the size change. In this case you need to now the current size of the ArrayList since you want to react when the size is 2, so a simple solution to this is doing the following:

ArrayListProperty.java

public class ArrayListProperty extends ArrayList implements ObservableValue {
    private ExpressionHelper helper = null;
    private SimpleIntegerProperty sizeProperty;

    public ArrayListProperty(){
        super();
        sizeProperty = new SimpleIntegerProperty(0);
    }

    @Override
    public boolean add(E e) {
        boolean returnValue = super.add(e);
        sizeProperty.set(size());
        fireValueChangedEvent();
        return returnValue;
    }

    @Override
    public void add(int index, E element) {
        super.add(index, element);
        sizeProperty.set(size());
        fireValueChangedEvent();
    }

    @Override
    public E remove(int index) {
        E returnValue = super.remove(index);
        sizeProperty.set(size());
        fireValueChangedEvent();
        return returnValue;
    }

    @Override
    public boolean remove(Object o) {
        boolean returnValue = super.remove(o);
        if(returnValue){
            sizeProperty.set(size());
            fireValueChangedEvent();
        }
        return returnValue;
    }

    protected void fireValueChangedEvent(){
        ExpressionHelper.fireValueChangedEvent(helper);
    }

    @Override
    public void addListener(ChangeListener listener) {
        helper = ExpressionHelper.addListener(helper, sizeProperty, listener);
    }

    @Override
    public void removeListener(ChangeListener listener) {
        helper = ExpressionHelper.removeListener(helper, listener);
    }

    @Override
    public Number getValue() {
        return null;
    }

    @Override
    public void addListener(InvalidationListener listener) {
        helper = ExpressionHelper.addListener(helper, sizeProperty, listener);
    }

    @Override
    public void removeListener(InvalidationListener listener) {
        helper = ExpressionHelper.removeListener(helper, listener);
    }
}

In this case the observable is the size of the array, then, when declaring your arraylist, you can add a listener and act when the size is 2.

ArrayListProperty