Java supports inheritance as its core functionality and then to achieve a lot of OOPs principles like abstraction using inheritance.

A class can extend another class using extends keyword and can inherit from an interface using implements keywords.

The access modifiers define rules for the member variables and methods of a class about their access from other classes (or anywhere in the code).

There are four access modifiers:

• private
• public
• protected
• default (No keyword required)

You can read more about them here

These concepts are very similar and are often confused.

• Inheritance means that the child has IS-A relationship with the parent class.

interface Animal() {
    public void bark();
}

class Dog implements Animal {
    public void bark() {
        System.out.println("Bark");
    }
}

Here, Dog IS-A Animal

• Composition represents a HAS-A relationship.

interface Engine {

}

class Car {
    private Engine engine;
}

Here, Car HAS-A Engine