Joshua Bloch

The Boolean.valueOf(boolean) method illustrates this technique: it never creates an object. This technique is similar to the Flyweight pattern [Gamma95]. It can greatly improve performance if equivalent objects are requested often, especially if they are expensive to create.

when is it appropriate to override equals? It is when a class has a notion of logical equality that differs from mere object identity and a superclass has not already overridden equals.

providing a good toString implementation makes your class much more pleasant to use and makes systems using the class easier to debug.