The System.identityHashCode (Object) method is an easy way to obtain the hash code that would have been provided for a particular object if that object’s class did not override the hashCode ...

The HashMap tutorial also includes some useful code snippets that help developers understand what's going on with a Java HashMap under the covers. For example, the following code used in the tutorial ...

Many Java developers follow the Joshua Bloch’s advice for implementing these methods as described in Effective Java (where 18 pages of the core 315 pages are devoted to these two methods).