ArrayList removeAll() not removing objects

Question

I have the simple ArrayLists of the member class:

ArrayList mGroupMembers = new ArrayList<>();
ArrayList mFriends = new Arr         


        

Answer 1

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

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