Knowledge Cafe

We will discuss about hashcode() and equals() methods of Object class and what role they play in an object life cycle. The methods  hashCode()  and  equals()  play a distinct role in the objects identity you insert into collections. The specific contract rules of these two methods are best described in the JavaDoc, here I will just describe what role they play, What they are used for, so you know why their implementation is important. Both equals() and hashcode()   are defined in  java.lang.Object  class and their default implementation is based upon Object information e.g. default  equals()  method return  true,  if two objects are exactly same i.e. they are pointing to same memory address, while default implementation of hashcode method return  int  and implemented as native method. Equals: This particular method is used to make equal comparison between two objects. There are two types of compari...

Equals and hashcode methods are two primary but yet one of most important methods for java developers to be aware of. Java intends to provide equals and hashcode for every class to test the equality and to provide a hash or digest based on content of class. Importance of hashcode increases when we use the object in different collection classes which works on hashing principle e.g. hashtable and hashmap. A well written hashcode method can improve performance drastically by distributing objects uniformly and avoiding collision. General Contracts for hashCode() in Java  1) If two objects are  equal  by equals() method then there  hashcode  returned by hashCode() method must be same. 2) Whenever  hashCode() mehtod  is invoked on the same object more than once within single execution of application, hashCode() must return same integer provided no information or fields used in equals and hashcode is modified. This integer is not required to be same during multiple execution of application th...