Why you should worry about that?

• or not.

Is-A (Inheritance)

Represents an “is-a-kind-of” hierarchy between classes.
A subclass (child class) inherits attributes and methods from its superclass (parent class).
Subclasses can specialize or override inherited behavior.
Declared using the extends keyword.

Has-A (Composition)

Represents a “has-a” part-whole relationship between objects.
One class (whole) contains a reference (member variable) to an object of another class (part).
The whole object can control the lifetime of the part object.
Implemented by creating an instance variable of the “part” class within the “whole” class.

References

https://www.geeksforgeeks.org/abstraction-in-java-2/
https://stackoverflow.com/questions/36162714/what-is-the-difference-between-is-a-relationship-and-has-a-relationship-in
https://www.acs.ase.ro/Media/Default/documents/java/ClaudiuVinte/books/ArnoldGoslingHolmes06.pdf#page=64.50