Java Abstraction

Java Abstraction

Abstraction hides implementation details and only shows what is important. In Java you do this with abstract classes and abstract methods.

Abstract classes

• An abstract class cannot create objects.
• You must inherit from it.
• It can have both normal and abstract methods.

Abstract methods

An abstract method has no body, only a signature. The subclass must provide the body:

abstract class Animal {
  public abstract void animalSound();

  public void sleep() {
    System.out.println("Zzz");
  }
}

class Pig extends Animal {
  public void animalSound() {
    System.out.println("The pig says: wee wee");
  }
}

Why abstract

• Force subclasses to implement specific methods.
• Define a common template while leaving details to subclasses.
• Helpful for large projects and teamwork.

Rules

• An abstract method must be in an abstract class.
• A subclass of an abstract class must implement all abstract methods (or also be abstract).

TL;DR

• Abstract classes cannot be instantiated.
• Abstract methods have a signature but no body.
• Subclasses must implement abstract methods.