Why do we have to override the equals method in Java

Question

I have some confusion about the reason that we override the  equals method   For example   Test test1   new Test 3   Test test2   new Test 3      The if comparison does the same thing that the overridden   equals    method does  if test1 equals test2        System out println  test1 and test2 are true in  equals            Override  equals method  public boolean equals Object object        if object instanceof Test  amp  amp    Test object  getValue      this t            return true        else           return false            I do not understand why we have to override the  equals   method

User · Answer

equals   doesn t perform an intelligent comparison for most classes unless the class overrides it  If it s not defined for a  user  class  it behaves the same as      Reference  http   www leepoint net notes-java data expressions 22compareobjects html http   www leepoint net data expressions 22compareobjects html

User · Answer

From the article Override equals and hashCode in Java      Default implementation of equals   class provided by java lang Object compares memory location and only return true if two reference variable are pointing to same memory location i e  essentially they are same object        Java recommends to override equals and hashCode method if equality is going to be defined by logical way or via some business logic  example       many classes in Java standard library does override it e g  String overrides equals   whose implementation of equals   method return true if content of two String objects are exactly same      Integer wrapper class overrides equals to perform numerical comparison etc

User · Answer

Object equals   method checks only reference of object not primitive data type or Object value  Wrapper class object of primitive data  simple primitive data type  byte  short  int  long etc     So that we must override equals   method when we compare object based on primitive data type

User · Answer

This should be enough to answer your question  http   docs oracle com javase tutorial java IandI objectclass html  The equals   method compares two objects for equality and returns true if they are equal  The equals   method provided in the Object class uses the identity operator      to determine whether two objects are equal  For primitive data types  this gives the correct result  For objects  however  it does not  The equals   method provided by Object tests whether the object references are equal   that is  if the objects compared are the exact same object  To test whether two objects are equal in the sense of equivalency  containing the same information   you must override the equals   method    Partial quote - click through to read examples

User · Answer

To answer your question  firstly I would strongly recommend looking at the Documentation   Without overriding the equals   method  it will act like       When you use the      operator on objects  it simply checks to see if those pointers refer to the same object  Not if their members contain the same value   We override to keep our code clean  and abstract the comparison logic from the If statement  into the object  This is considered good practice and takes advantage of Java s heavily Object Oriented Approach

User · Answer

The default behavior for java lang Object is to compare references  but that s not appropriate for every kind of object  There are things called Value Objects  like BigDecimal or String   where objects with the same value are considered to be interchangeable  so the default behavior of equals is not desirable  Those kinds of objects have to implement equals and hashcode based on the value that the object takes on

User · Answer

By default  equals   uses    identity function to compare which obviously doesn t work as the instances test1 and test2 are not the same     only works with primitive data types like int or string  So you need to override it to make it work by comparing all the member variables of the Test class

User · Answer

Let me give you an example that I find very helpful  You can think of reference as the page number of a book  Suppose now you have two pages a and b like below   BookPage a   getSecondPage    BookPage b   getThirdPage     In this case  a    b will give you false  But  why  The reason is that what    is doing is like comparing the page number  So  even if the content on these two pages is exactly the same  you will still get false  But what do we do if you we want to compare the content  The answer is to write your own equals method and specify what you really want to compare

[java] Why do we have to override the equals() method in Java?

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