How does a Java HashMap handle different objects with the same hash code?

Question

As per my understanding I think:

1. It is perfectly legal for two objects to have the same hashcode.
2. If two objects are equal (using the equals() method)

Answer 1

The hashcode determines which bucket for the hashmap to check. If there is more than one object in the bucket then a linear search is done to find which item in the bucket equals the desired item (using the equals()) method.

In other words, if you have a perfect hashcode then hashmap access is constant, you will never have to iterate through a bucket (technically you would also have to have MAX_INT buckets, the Java implementation may share a few hash codes in the same bucket to cut down on space requirements). If you have the worst hashcode (always returns the same number) then your hashmap access becomes linear since you have to search through every item in the map (they're all in the same bucket) to get what you want.

Most of the time a well written hashcode isn't perfect but is unique enough to give you more or less constant access.