ArrayList removeAll() not removing objects

You have to know that

ArrayList#removeAll(Collection)

makes a call to

ArrayList#contains(Object)

which makes a call to

ArrayList#indexOf(Object)

which finally calls

Object#equals

---

So if equals is not correctly overridden (following the equals contract rules), you're not getting the correct behaviour.

How are 2 members determined to be equal? I'm guessing if they have the same ID, you deem them equal, however java wants them to be the exact same reference in memory which may not be the case. To correct for this you can override the equals function to have it return if the ids are equal:

public class Member {
    //..

    @Override
    public boolean equals(Object anObject) {
        if (!(anObject instanceof Member)) {
            return false;
        }
        Member otherMember = (Member)anObject;
        return otherMember.getUserUID().equals(getUserUID());
    }
}

Also when you override .equals it is recommended to also override hashCode so that the objects also work correctly in hashing functions like Set or Map.