Learning Java from 0 to Senior 5/100: Interfaces and Abstract Classes

Interfaces and Abstract Classes — Structuring Complex Java Applications

Introduction to Abstraction in Java

Abstraction, a key concept in object-oriented programming, allows complex real-world ideas to be represented in simpler, more manageable forms. In Java, abstraction is achieved using abstract classes and interfaces, enabling objects to be defined in terms of their high-level functionality rather than their detailed workings.

Abstract Classes: The Partial Blueprint

Abstract classes are declared using the abstract keyword and are incomplete by themselves. They require subclasses to provide implementations for the abstract methods.

abstract class Animal {
    // Abstract method (does not have a body)
    public abstract void animalSound();
    
    // Regular method
    public void sleep() {
        System.out.println("Zzz");
    }
}

Classes that inherit from an abstract class:

1. Must implement all abstract methods, or
2. Become abstract classes themselves.

Interfaces: Complete Abstraction