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Java / Map and its implementations

Difference between HashMap and IdentityHashMap.
HashMap. IdentityHashMap.
HashMap uses equals method to compare keys. IdentityHashMap uses == operator to compare its keys.
HashMap uses hashcode method to find bucket location. IdentityHashMap uses System.identityHashCode(object) to find bucket location.
HashMap may not be faster when compared to IdentityHashMap as it uses equals method for key comparison. IdentityHashMap may be faster than HashMap as it doesn't use equals method..
HashMap keys need to be immutable. IdentityHashMap doesn't require the key object to be immutable as it doesn't use hashcode or equals method.

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