Explain Java hashCode() and equals() method.

equals() method is used to determine the equality of two Java objects. When we have a custom class we need to override the equals() method and provide an implementation so that it can be used to find the equality between two instance of it. By Java specification there is a contract between equals() and hashCode().

It says, "if two objects are equal, that is obj1.equals(obj2) is true then, obj1.hashCode() and obj2.hashCode() must return same integer".

Whenever we choose to override equals(), then we must override the hashCode() method. hashCode() is used to calculate the position bucket and keys.