ToyMessageBus.java

package com.novoda.example.MemoryLeaker;

import java.util.HashSet;
import java.util.Set;

public class ToyMessageBus {
    private static ToyMessageBus instance;
    private final Set<Object> listeners = new HashSet<Object>();

    private ToyMessageBus() {}

    public static ToyMessageBus getInstance() {
        // implementing this method correctly would require a separate blog post.
        if(instance == null) {
            instance = new ToyMessageBus();
        }
        return instance;
    }

    public void register(Object o) {
        listeners.add(o);
    }

    public void unregister(Object o) {
        listeners.remove(o);
    }
}