Compare two objects with equals and operator

Question

I constructed a class with one String field  Then I created two objects and I have to compare them using    operator and  equals   too  Here s what I ve done   public class MyClass        String a       public MyClass String ab            a   ab             public boolean equals Object object2            if a    object2                 return true                    else return false             public boolean equals2 Object object2            if a equals object2                 return true                    else return false               public static void main String   args             MyClass object1   new MyClass  test            MyClass object2   new MyClass  test             object1 equals object2           System out println object1 equals object2             object1 equals2 object2           System out println object1 equals2 object2                After compile it shows two times false as a result  Why is it false if the two objects have the same fields -  test

User · Answer

It looks like equals2 is just calling equals  so it will give the same results

User · Answer

Here the output will be false   false beacuse in first sopln statement you are trying to compare a string type varible of Myclass type to the other MyClass type and it will allow because of both are Object type and you have used      oprerator which will check the reference variable value holding the actual memory not the actual contnets inside the memory    In the second sopln also it is the same as you are again calling a equals object2  where a is a varible inside object1   Do let me know your findings on this

User · Answer

You should override equals    public boolean equals  Object obj         if  this  obj  return true       if  this    null  return false       if  this getClass      obj getClass    return false          Class name is Employ  amp  have lastname      Employe emp    Employee  obj        return this lastname equals emp getlastname

User · Answer

The overwrite function equals   is wrong  The object  a  is an instance of the String class and  object2  is an instance of the MyClass class  They are different classes  so the answer is  false

User · Answer

IN the below code you are calling the overriden method  equals     public boolean equals2 Object object2        if a equals object2        here you are calling the overriden method  that is why you getting false 2 times          return true            else return false

User · Answer

the return type of object equals is already boolean  there s no need to wrap it in a method with branches  so if you want to compare 2 objects simply compare them   boolean b   objectA equals objectB     b is already either true or false

User · Answer

If you dont need to customize the default toString   function  another way is to override toString   method  which returns all attributes to be compared  then compare toString   output of two objects  I generated toString   method using IntelliJ IDEA IDE  which includes class name in the string    public class Greeting   private String greeting    Override public boolean equals Object obj        if  this    obj  return true      return this toString   equals obj toString         Override public String toString         return  Greeting                  greeting      greeting

User · Answer

compares object references  it checks to see if the two operands point to the same object  not equivalent objects  the same object    If you want to compare strings  to see if they contain the same characters   you need to compare the strings using equals   In your case  if two instances of MyClass really are considered equal if the strings match  then   public boolean equals Object object2        return object2 instanceof MyClass  amp  amp  a equals   MyClass object2  a          but usually if you are defining a class  there s more to equivalency than the equivalency of a single field  a in this case      Side note  If you override equals  you almost always need to override hashCode  As it says in the equals JavaDoc      Note that it is generally necessary to override the hashCode method whenever this method is overridden  so as to maintain the general contract for the hashCode method  which states that equal objects must have equal hash codes

User · Answer

The best way to compare 2 objects is by converting them into json strings and compare the strings  its the easiest solution when dealing with complicated nested objects  fields and or objects that contain arrays   sample   import com google gson Gson    Object a           Object b          String objectString1   new Gson   toJson a   String objectString2   new Gson   toJson b     if objectString1 equals objectString2          do this

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Your class might implement the Comparable interface to achieve the same functionality  Your class should implement the compareTo   method declared in the interface   public class MyClass implements Comparable lt MyClass gt        String a       public MyClass String ab           a   ab                returns an int not a boolean     public int compareTo MyClass someMyClass                The String class implements a compareTo method  returning a 0             if the two strings are identical  instead of a boolean             Since  a  is a string  it has the compareTo method which we call            in MyClass s compareTo method                      return this a compareTo someMyClass a               public static void main String   args            MyClass object1   new MyClass  test            MyClass object2   new MyClass  test             if object1 compareTo object2     0               System out println  true                      else              System out println  false

User · Answer

When we use      the Reference of object is compared not the actual objects  We need to override equals method to compare Java Objects    Some additional information C   has operator over loading  amp  Java does not provide operator over loading  Also other possibilities in java are implement Compare Interface  which defines a compareTo method    Comparator interface is also used compare two objects

User · Answer

The      operator returns true only if the two references pointing to the same object in memory  The equals   method on the other hand returns true based on the contents of the object   Example   String personalLoan   new String  cheap personal loans    String homeLoan   new String  cheap personal loans       since two strings are different object result should be false boolean result   personalLoan    homeLoan  System out println  Comparing two strings with    operator      result      since strings contains same content   equals   should return true result   personalLoan equals homeLoan   System out println  Comparing two Strings with same content using equals method      result    homeLoan   personalLoan    since both homeLoan and personalLoan reference variable are pointing to same object        should return true result    personalLoan    homeLoan   System out println  Comparing two reference pointing to same String with    operator      result     Output  Comparing two strings with    operator  false Comparing two Strings with same content using equals method  true Comparing two references pointing to same String with    operator  true  You can also get more details from the link  http   javarevisited blogspot in 2012 12 difference-between-equals-method-and-equality-operator-java html m 1

User · Answer

Statements a    object2 and  a equals object2  both will always return false because a is a string while object2 is an instance of MyClass

User · Answer

Your equals2   method always will return the same as equals       Your code with my comments   public boolean equals2 Object object2        equals2 method     if a equals object2        if equals   method returns true         return true     return true           else return false     if equals   method returns false  also return false

User · Answer

Your implementation must like   public boolean equals2 Object object2        if a equals object2 a             return true            else return false      With this implementation your both methods would work

[java] Compare two objects with .equals() and == operator

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