Does Map Support User-Defined Object As Key?

Question

Hi,
Map m = new HashMap();
m.put(myobj1, "Hello");
m.put(myobj2, "World");
I'm using my own object as the key for the map.
Since the key is a user-defined object, I would need to overload the equality operator in order to get the value.
Now, if I would to do something like this:
MyObj myObj = (MyObj)m.get(myobj3);
I found out that the equality operator for MyObj never even executes (by printing out some message). But if I would to retrieve using the original myobj1 and myobj2 object, then only the equality operator would get executed.
If I would to do the above using the String object instead of MyObj, the equality operator works fine.
I can't seemed to find a reason for the above behaviour. Any ideas?
Thanks in advance.

Answer 1

In a hashmap, the object is located/stored by calculating its hash code. Therefore, you need to also override the hashCode() method of the Object class so that the same objects return the same hashCode, so that you can retrieve your objects.