Java IdentityHashMap: Purpose and Uses

The IdentityHashMap class in Java is a unique type of hash map that determines the equality of objects based on reference equality (i.e., the object’s memory address) rather than relying on the objects’ equals() and hashCode() methods.

IdentityHashMap allows storing objects where the equals() method returns true but the hashCode() method returns different values. In regular HashMap or HashSet, equal objects must have equal hashCode values, but in IdentityHashMap, equal objects can have different hashCode values. This is useful in scenarios where object equality needs to be determined based on memory address.

Normally, we use HashMap or HashSet to store objects because they use the equals() method and hashCode() method to determine object equality. In some cases, we may need to determine object equality based on memory address, in which case we can use IdentityHashMap.

It is important to note that IdentityHashMap may be slightly faster in performance compared to HashMap when using reference equality to determine object equality. However, since it does not consider the objects’ hash code values, its performance in operations such as searching, inserting, and deleting may be affected. Therefore, it is necessary to balance performance and requirements when using IdentityHashMap.