What limitations does the hashCode method have in Java?

The hashCode() method in Java has the following limitations:

• Does not guarantee uniqueness: different objects can have the same hash code (collisions). Therefore, hashCode() should not be used as a unique identifier.

• Must be consistent with equals(): if two objects are equal according to the equals() method, then their hashCode() must return the same value. Violating this contract can lead to incorrect behavior of collections, such as HashMap.

• Value can change: if fields involved in computing hashCode() are modified, the hash code of the object will also change. This is dangerous if the object is used in hash-based structures (e.g., HashSet), as it breaks data integrity.

• Not mandatory to override: if not overridden, the implementation from Object is used, which usually returns the memory address of the object, which may not be suitable for application logic.

Example of correct overriding:

@Override
public int hashCode() {
    return Objects.hash(field1, field2);
}

Thus, hashCode() is an auxiliary method for optimizing search in collections, but it does not guarantee uniqueness and requires adherence to the contract with equals().