Hashcode and Equals method

Both methods are declared in Object.java (which is parent for all the java classes)

Below snapshot taken from Object.java file

 public boolean equals(Object o) {  
     return this == o;  
   }  
 public int hashCode() {  
     int lockWord = shadow$_monitor_;  
     final int lockWordMask = 0xC0000000; // Top 2 bits.  
     final int lockWordStateHash = 0x80000000; // Top 2 bits are value 2 (kStateHash).  
     if ((lockWord & lockWordMask) == lockWordStateHash) {  
       return lockWord & ~lockWordMask;  
     }  
     return System.identityHashCode(this);  
   }  

Equals method : To check the equality of the two object
    from the above code , if you are not overriding the equals method, then it will check memory address rather than the object . 

  Assume you have a employee class where emp_id is unique , then you need to override the eqquls like below 

 @Override

 public boolean equals(Object o) {  
     return this.emp_id == o.emp_id;  
   }  

Hashcode method : 
       hashcode method will comes in to the picture , if you are using this class's object  as a key in hashmap.
you no need to override this method if you are not using this class as a key.

Nowadays, modern editor will implement hashcode() for you to get the decent hashcode value.


Ok, now we have seen hashcode and equals method separately.. 
  Now ,Question is , any contract between this two method ...

Contract between the two methods Yes ,  in case two object is equal , then hashcode value should be same.
         if hashcode of the two object is same , then object may or may not be equal.

Well, to understand the above statement , we need to know the internal implementation of the hashmap and how read and write happens.

will talk about the those topic soon. stay tuned.