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Effective Java(TM) Programming Language Guide

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Perhaps a later release of the Java platform will provide stateof. theart hash functions for its classes and utility methods to allow average program ...

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Effective Java(TM) Programming Language GuidePage 125C H A P T E R3Methods Common to All ObjectsALTHOUGHObjectis a concrete class it is designed primarily for extension. Allof its nonfinal methods (equals hashCode toString clone andfinalize) haveexplicit general contracts because they are designed to be overridden. It is theresponsibility of any class overriding these methods to obey their general contracts; failure to do so will prevent other classes that depend on these contractsfrom functioning properly in conjunction with the class.This chapter tells you when and how to override the nonfinalObjectmethods.Thefinalizemethod is omitted from this chapter because it was discussed inItem 6. While not anObjectmethodComparable.compareTois discussed in thischapter because it has a similar character.Item 7: Obey the general contract when overridingequalsOverriding the equalsmethod seems simple but there are many ways to get itwrong and the consequences can be dire. The easiest way to avoid problems is notto override theequalsmethod in which case each instance is equal only to itself.This is the right thing to do if any of the following conditions apply: Each instance of the class is inherently unique. This is true for classes thatrepresent active entities rather than values such asThread. Theequalsimplementation provided by Objecthas exactly the right behavior for these classes. You dont care whether the class provides a logical equality test. Forexamplejava.util.Randomcould have overridden equalsto check whethertwo Randominstances would produce the same sequence of random numbersgoing forward but the designers didnt think that clients would need or wantthis functionality. Under these circumstances theequalsimplementationinherited fromObjectis adequate.Page 2CHAPTER 3 METHODS COMMON TO ALL OBJECTS26 A superclass has already overriddenequalsand the behavior inheritedfrom the superclass is appropriate for this class. For example mostSetimplementations inherit theirequals ...

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