The answer is simple; a little education is in order.

Hash maps/tables work by taking an object and 'hashing' it with a 'hash' function to produce a Psuedo Random Uniformly Distributed unique id representing the object where said id can be used as a key into an indexable structure like an array. Ideally you would have a perfect hash where each unique item produces a unique indexable id.

Obviously your array is fixed in size (you can grow the array but this will dramatically affect runtime performance) so at some point, if you continue to add elements to the Hash map/table you will eventually get 2 items with the same hash code and then you will have a collision; this is where equals comes into play.

When this occurs equality is used to disambiguate WHICH key/value you are seeking by iterating through (usually by storing a LinkedList at the index position and not just the element) the available objects and checking the equals method.

So, the problem for your case is easy: Your hash implementation is wrong and thus HashSet (which is backed by HashMap) fails to find your object in it's table and thus never bothers to call equals (have a look at HashMap.get() to see their implementation).

Whatever you use in equals MUST be used in hashCode() if you want this to work and vice versa. If you implement equals() it's a damn good idea to implement hashCode(). If you implement hashCode() then you MUST implement equals for hashing to actually work.

Hash maps/tables work by taking an object and 'hashing' it with a 'hash' function to produce a Psuedo Random Uniformly Distributed unique id representing the object where said id can be used as a key into an indexable structure like an array. Ideally you would have a perfect hash where each unique item produces a unique indexable id.

Obviously your array is fixed in size (you can grow the array but this will dramatically affect runtime performance) so at some point, if you continue to add elements to the Hash map/table you will eventually get 2 items with the same hash code and then you will have a collision; this is where equals comes into play.

When this occurs equality is used to disambiguate WHICH key/value you are seeking by iterating through (usually by storing a LinkedList at the index position and not just the element) the available objects and checking the equals method.

So, the problem for your case is easy: If your hash implementation is wrong then HashSet (which is backed by HashMap) fails to find your object in it's table and thus never bothers to call equals (have a look at HashMap.get() to see their implementation).

Whatever you use in equals MUST be used in hashCode() if you want this to work and vice versa. If you implement equals() it's a damn good idea to implement hashCode(). If you implement hashCode() then you MUST implement equals for hashing to actually work.