What is double equal(==) operator and equals() method in java?

There are following difference between double equal(==) operator and equals() method in java.

Equals() method:—

equals() method compare the content value of two String object. this method is available in java.lang package.

  • This method is only applicable for object reference but not for primitive.
  • We can override equals() method for content comparison.
  • If we are apply equals() method for heterogeneous object then we would get compile time or run time exception.
  • To any object reference like m, m.equals(null) is always return false.
				
					public class EqualityTest {
	public static void main(String[] args) {
		
		String s1 = new String("well");
		String s2 = new String("well");
		System.out.println(s1.equals(s2));
	}
}

Output:- true

== Operator method :-

It is compare the reference value of two object.it return true when both object pointing to the same memory location.

  • This operator is applicable for both primitive and object reference.
  • We can not override ‘==’ operator for content comparison.
  • If we are applying ‘==’ operator for heterogeneous object then we will get incompatible type exception.
  • For ant object reference like h, h==null is always return false.
				
					public class B {
	String name;

	B(String name) {
		this.name = name;
	}
}

public class EqualityTest {
	public static void main(String[] args) {
		
		B b1 = new B("well");
		B b2 = new B("well");
		System.out.println(b1 == b2);
		String s1 = "test";
		String s2 = "test";
		System.out.println(s1 == s2);
	}
}

Output:-
false
true

Above first output is false because b1 and b2 are two different object.
Second output is true because s1 and s2 String object is reference same object.