How does a ArrayList's contains() method evaluate objects?

Question

Say I create one object and add it to my ArrayList. If I then create another object with exactly the same constructor input, will the contains() me

Answer 1

Generally you should also override hashCode() each time you override equals(), even if just for the performance boost. HashCode() decides which 'bucket' your object gets sorted into when doing a comparison, so any two objects which equal() evaluates to true should return the same hashCode value(). I cannot remember the default behavior of hashCode() (if it returns 0 then your code should work but slowly, but if it returns the address then your code will fail). I do remember a bunch of times when my code failed because I forgot to override hashCode() though. :)