Effective Java, 3rd Edition

Chapter 3. Methods Common to All Objects

ALTHOUGH Object is a concrete class, it is designed primarily for extension. All of its nonfinal methods (equals, hashCode, toString, clone, and finalize) have explicit general contracts because they are designed to be overridden. It is the responsibility of any class overriding these methods to obey their general contracts; failure to do so will prevent other classes that depend on the contracts (such as HashMap and HashSet) from functioning properly in conjunction with the class.

This chapter tells you when and how to override the nonfinal Object methods. The finalize method is omitted from this chapter because it was discussed in Item 8. While not an Object method, Comparable.compareTo is discussed ...