Difference between comparing String using == and .equals() method in Java – GeeksforGeeks

Both equals() method and the == operator are used to compare two objects in Java. == is an operator and equals() is method. But == operator compares reference or memory location of objects in a heap, whether they point to the same location or not.
Whenever we create an object using the operator new, it will create a new memory location for that object. So we use the == operator to check memory location or address of two objects are the same or not.

In general, both equals() and “==” operators in Java are used to compare objects to check equality, but here are some of the differences between the two: 

  1. The main difference between the .equals() method and == operator is that one is a method, and the other is the operator.
  2. We can use == operators for reference comparison (address comparison) and .equals() method for content comparison. In simple words, == checks if both objects point to the same memory location whereas .equals() evaluates to the comparison of values in the objects.
  3. If a class does not override the equals method, then by default, it uses the equals(Object o) method of the closest parent class that has overridden this method. See Why to Override equals(Object) and hashCode() method? in detail.

Java




 

public class Test {

    public static void main(String[] args)

    {

        String s1 = "HELLO";

        String s2 = "HELLO";

        String s3 =  new String("HELLO");

 

        System.out.println(s1 == s2);

        System.out.println(s1 == s3);

        System.out.println(s1.equals(s2));

        System.out.println(s1.equals(s3));

    }

}



Output

true
false
true
true

Explanation: Here, we create two objects, namely s1 and s2. 

  • Both s1 and s2 refer to same objects.
  • When we use the == operator for s1 and s2 comparison, the result is true as both have the same addresses in the string constant pool.
  • Using equals, the result is true because it’s only comparing the values given in s1 and s2.

 Java String Pool

s1 = “HELLO”

s2 = “HELLO”

Java Heap

s3 = “HELLO”

Let us understand both the operators in detail:

Equality operator(==)

We can apply equality operators for every primitive type, including the boolean type. We can also apply equality operators for object types. 

Java




 

class Test {

    public static void main(String[] args)

    {

        

        System.out.println(10 == 20);

 

        

        System.out.println('a' == 'b');

 

        

        System.out.println('a' == 97.0);

 

        

        System.out.println(true == true);

    }

}



Output

false
false
true
true

If we apply == for object types then, there should be compatibility between arguments types (either child to parent or parent to child or same type). Otherwise, we will get a compile-time error. 

Java




 

class Test {

    public static void main(String[] args)

    {

        Thread t = new Thread();

        Object o = new Object();

        String s = new String("GEEKS");

 

        System.out.println(t == o);

        System.out.println(o == s);

 

       

       System.out.println(t==s);

    }

}



Output: 

false
false
// error: incomparable types: Thread and String

.equals() Method

In Java, the String equals() method compares the two given strings based on the data/content of the string. If all the contents of both the strings are the same, it returns true. If all characters are not matched, then it returns false. 

Java




public class Test {

    public static void main(String[] args)

    {

        Thread t1 = new Thread();

        Thread t2 = new Thread();

        Thread t3 = t1;

 

        String s1 = new String("GEEKS");

        String s2 = new String("GEEKS");

 

        System.out.println(t1 == t3);

        System.out.println(t1 == t2);

        System.out.println(s1 == s2);

 

        System.out.println(t1.equals(t2));

        System.out.println(s1.equals(s2));

    }

}



Explanation: Here, we are using the .equals method to check whether two objects contain the same data or not. 

  • In the above example, we create 3 Thread objects and 2 String objects.
  • In the first comparison, we check whether t1 == t3 or not. As we know that both t1 and t3 point to the same object. That’s why it returns true.
  • In the second comparison, we are using the operator “==” for comparing the String Objects and not the contents of the objects. Here, both the objects are different, and hence the outcome of this comparison is “False.”
  • When we are comparing 2 String objects by .equals() operator, then we are checking that is both objects contain the same data or not.
  • Both the objects contain the same String, i.e., GEEKS. That’s why it returns true.

This article is contributed by Veturi Lakshmi Prathyusha. If you like GeeksforGeeks and would like to contribute, you can also write an article using write.geeksforgeeks.org or mail your article to review-t[email protected] See your article appearing on the GeeksforGeeks main page and help other Geeks. Please write comments if you find anything incorrect, or you want to share more information about the topic discussed above.

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