equals is a method in Object class..
By default in java all the classes extend object class so 
any two object can be compared using the equals method...

Provided user implement their own equals method(Override), 
because the original equals method compares two objects by 
their reference..

If you have a class

class A
{
  int value;
    p s v m(String args[]){
    A obj1= new A();
    abj1.value = 10;
    A obj2= new A();
    abj2.value = 10;
    
   // now if try to compare these two classes 

    sop(obj1.equals(obj2))  // Result will be always false
 }                          //unless you override
                             the equals method
 
    boolean equals(A a){
      if (a.value == this.value)
       return true;
      else
        return false;
    }//Placing this method in the above class will override 
        the equals method and you will be able to compare 
        actually the properties of those two object not 
        their references.