A covariant return type of a method is one that can be replaced by a "narrower" type when the method is overridden in a subclass.

Let say class B is child of class A. 

There is a get() method in class A as well as class B.

 get() method of class A can return an instance

of A, and get() method of class B return an instance of B. Here

class B overrides get() method, but the return type is different.

Before Java 5, any method that overrides the method of parent class

would have same return type.

From Java 5 onwards, a child class can override a method of parent

class and the child class method can return an object that is child of

object return by parent class method.

https://www.tutorialspoint.com/Covariant-return-types-in-Java#:~:text=Covariant%20return%20type%20refers%20to,for%20non%2Dprimitive%20return%20types.