Question

I would like a Map implementation in which i could add listeners for put() events.

Is there anything like that in the standard or any 3rd party libraries?

Answer 1

I’m not aware of any standard or 3rd party, but it is easy, just create a class which wraps another Map and implements the Map interface:

public class MapListener<K, V> implements Map<K, V> {

    private final Map<K, V> delegatee;

    public MapListener(Map<K, V> delegatee) {
        this.delegatee = delegatee;
    }

    // implement all Map methods, with callbacks you need.

}