IS-A relationship in OOP Java?

In OOP, IS-A relationship is completely inheritance . This means, that the child class is a type of parent class. For example, an apple is a fruit. So you will extend fruit to get apple.

In knowledge representation, object-oriented programming and design (see object-oriented program architecture), is-a (is_a or is a) is a subsumption relationship between abstractions (e.g. types, classes), wherein one class A is a subclass of another class B (and so B is a superclass of A) .

An IS-A relationship is inheritance. The classes which inherit are known as sub classes or child classes. On the other hand, HAS-A relationship is composition. In OOP, IS-A relationship is completely inheritance .