what must be hashcode of null objects in Java?

Question

According to a comment from this post, hascode of null objects can throw NPE or a value of zero. This is implementation speci

Answer 1

As the javadoc says:

Objects.hashCode(Object o)

Returns the hash code of a non-null argument and 0 for a null argument.

p2.hashCode() throws a NullPointerException because you are trying to access a method of a null object.