IdentityHashMap in Java: Key Uses

IdentityHashMap in Java is a unique implementation of the HashMap class that distinguishes itself from regular HashMaps by using the “==” operator to determine if two keys are equal, instead of using the equals method.

The uses of the IdentityHashMap include:

1. Use in situations where object reference equality needs to be considered instead of logical equality. In some cases, two objects may have the same content but are different instances. Using IdentityHashMap can ensure distinguishing between these different instances.
2. Use when it is necessary to preserve the order of object references. Unlike HashMap, IdentityHashMap maintains the order of key insertion. This is useful for scenarios where iteration needs to be done in the order of insertion.
3. It is used in hash mappings that require object references. Unlike HashMap, IdentityHashMap calculates hash codes based on the memory address of the objects, rather than relying on the objects’ hashCode method. This ensures that object references used as keys have unique hash codes, avoiding hash collisions.

It is important to note that due to IdentityHashMap using the “==” operator to determine equality, rather than the equals method, it cannot be used for typical key-value operations. If object logical equality needs to be considered, HashMap or other map implementations that have an equals method should be used.