What is abstraction in Java?

Abstraction is a fundamental concept in object-oriented programming where the implementation details of a class are hidden from the user, and only the necessary information is exposed. In Java, this is achieved by using abstract classes and interfaces.

Abstract classes cannot be instantiated and can only be extended by concrete classes. They can contain both concrete and abstract methods, and are typically used to define a base class that provides a common interface for a group of related classes. Concrete classes that extend an abstract class must implement all the abstract methods defined in the abstract class.

Interfaces in Java are a way to achieve complete abstraction, as they only define the public methods that a class should implement without providing any implementation details. A class can implement any number of interfaces, and each interface can have any number of methods.

The main benefits of abstraction in Java are:

• It allows classes to be loosely coupled, which means that changes to one class do not affect the others.
• It promotes code reuse, as common functionality can be defined in abstract classes and interfaces and shared by multiple classes.
• It enables hiding implementation details, which makes the code more maintainable and easier to understand.

Here's an example:

public abstract class Animal {
    public abstract void makeSound();
}

public class Dog extends Animal {
    public void makeSound() {
        System.out.println("Woof!");
    }
}

public class Cat extends Animal {
    public void makeSound() {
        System.out.println("Meow!");
    }
}

In this example, the Animal class is an abstract class that defines a method makeSound. The Dog and Cat classes extend the Animal class and implement the makeSound method.