The hash value of the value, which allows the value to be an element of a hash-based set or key of a hash-based map. Implementations must respect the constraint that:

• if x==y then x.hash==y.hash.

Therefore, a class which refines equals must also refine hash.

A developer-friendly string representing the instance. Concatenates the name of the concrete class of the instance with the hash of the instance. Subclasses are encouraged to refine this implementation to produce a more meaningful representation.

Compares this value with the given value. Implementations must respect the constraints that:

• x==y if and only if x<=>y == equal (consistency with equals()),
• if x>y then y<x (symmetry), and
• if x>y and y>z then x>z (transitivity).

Determine if two values are equal. Implementations should respect the constraints that:

• if x===y then x==y (reflexivity),
• if x==y then y==x (symmetry),
• if x==y and y==z then x==z (transitivity).

Furthermore it is recommended that implementations ensure that if x==y then x and y have the same concrete class.

A class which explicitly refines equals() is said to support value equality, and the equality operator == is considered much more meaningful for such classes than for a class which simply inherits the default implementation of identity equality from Identifiable.