Java IdentityHashMap is a class that implements the Java Map interface and uses reference equality to compare keys, rather than the standard Java equals() method. This means that Java IdentityHashMap treats two objects as equal only if they are the exact same object in memory, not if they are logically equal. Introduced in Java 1997 with Java 1.2, IdentityHashMap is useful for scenarios where identity-based comparisons are required, such as in object caching or managing object identity.

https://docs.oracle.com/javase/8/docs/api/java/util/IdentityHashMap.html