This is called a key attribute!
There are different types of key attributes!
Primary key is the key that is actually chosen, for example a social security number.
There is also a unique key, say our finger prints! they also uniquely identify humans, but usually we prefer to use social security number when we list people (a unique key could be a primary key if we chose so)
We could also identify people by their social security number and a name, but this is unnecessary, as social security number already gives a full identification. Such a reduntant key is called super key.
Answer:- Major property of a good hash code is that objects which are equal should return the same hash code .
Explanation: Hash codes is a numeric value which is used for identify a object while a equality testing .Hash code can occupy the value of any length and then returns a fixed length value. The value of hash codes are variable.
If two objects are equal then by the method of equal(object) if the hashcode() function is called on both the objects , they produce the same value.
