What is the difference between == vs equals() in J

Question

I wanted to clarify if I understand this correctly:

• == -> is a reference comparison, i.e. both objects point to the same memory location
• .equals() -> evaluates to the comparison of values in the objects

Am I correct in my understanding ?

Answer 1

== operator always reference is compared. But in case of

equals() method

it's depends's on implementation if we are overridden equals method than it compares object on basic of implementation given in overridden method.

 class A
 {
   int id;
   String str;

     public A(int id,String str)
     {
       this.id=id;
       this.str=str;
     }

    public static void main(String arg[])
    {
      A obj=new A(101,"sam");
      A obj1=new A(101,"sam");

      obj.equals(obj1)//fasle
      obj==obj1 // fasle
    }
 }

in above code both obj and obj1 object contains same data but reference is not same so equals return false and == also. but if we overridden equals method than

 class A
 {
   int id;
   String str;

     public A(int id,String str)
     {
       this.id=id;
       this.str=str;
     }
    public boolean equals(Object obj)
    {
       A a1=(A)obj;
      return this.id==a1.id;
    }

    public static void main(String arg[])
    {
      A obj=new A(101,"sam");
      A obj1=new A(101,"sam");

      obj.equals(obj1)//true
      obj==obj1 // fasle
    }
 }

know check out it will return true and false for same case only we overridden

equals method .

it compare object on basic of content(id) of object

but ==

still compare references of object.

Answer 2

Both == and .equals() refers to the same object if you don't override .equals().

Its your wish what you want to do once you override .equals(). You can compare the invoking object's state with the passed in object's state or you can just call super.equals()

Answer 3

Just remember that .equals(...) has to be implemented by the class you are trying to compare. Otherwise, there isn't much of a point; the version of the method for the Object class does the same thing as the comparison operation: Object#equals.

The only time you really want to use the comparison operator for objects is wen you are comparing Enums. This is because there is only one instance of an Enum value at a time. For instance, given the enum

enum FooEnum {A, B, C}

You will never have more than one instance of A at a time, and the same for B and C. This means that you can actually write a method like so:

public boolean compareFoos(FooEnum x, FooEnum y)
{
    return (x == y);
}

And you will have no problems whatsoever.

Answer 4

You will have to override the equals function (along with others) to use this with custom classes.

The equals method compares the objects.

The == binary operator compares memory addresses.

Answer 5

Since Java doesn’t support operator overloading, == behaves identical for every object but equals() is method, which can be overridden in Java and logic to compare objects can be changed based upon business rules.

Main difference between == and equals in Java is that "==" is used to compare primitives while equals() method is recommended to check equality of objects.

String comparison is a common scenario of using both == and equals method. Since java.lang.String class override equals method, It return true if two String object contains same content but == will only return true if two references are pointing to same object.

Here is an example of comparing two Strings in Java for equality using == and equals() method which will clear some doubts:

public class TEstT{

    public static void main(String[] args) {

String text1 = new String("apple");
String text2 = new String("apple");

//since two strings are different object result should be false
boolean result = text1 == text2;
System.out.println("Comparing two strings with == operator: " + result);

//since strings contains same content , equals() should return true
result = text1.equals(text2);
System.out.println("Comparing two Strings with same content using equals method: " + result);

text2 = text1;
//since both text2 and text1d reference variable are pointing to same object
//"==" should return true
result = (text1 == text2);
System.out.println("Comparing two reference pointing to same String with == operator: " + result);

}
}

Answer 6

The major difference between == and equals() is

1) == is used to compare primitives.

For example :

        String string1 = "Ravi";
        String string2 = "Ravi";
        String string3 = new String("Ravi");
        String string4 = new String("Prakash");

        System.out.println(string1 == string2); // true because same reference in string pool
        System.out.println(string1 == string3); // false

2) equals() is used to compare objects. For example :

        System.out.println(string1.equals(string2)); // true equals() comparison of values in the objects
        System.out.println(string1.equals(string3)); // true
        System.out.println(string1.equals(string4)); // false