Abstraction

Data abstraction refers to the process of hiding low level details and only displaying important information. The abstract keyword is used to declare abstract classes. Abstract classes can have abstract and non-abstract methods.

Abstraction is achieved with the help of abstract classes and interfaces:

 

i. Abstract Classes and Abstract Methods:

Abstraction can be implemented only if we inherit the class from another class.

Inside the abstract class, when we create an abstract method, we use a semicolon (;) instead of curly brackets ({}).

Example:

abstract class Fruits {
    public abstract void taste();
    public void eat() {
        System.out.println("Let's eat Fruits.");
    }
}

class Mango extends Fruits {
    public void taste() {
        System.out.println("Mango is sweet.");
    }
}


public class Example3 {
    public static void main(String[] args) {
        Mango m = new Mango();
        m.eat();
        m.taste();
    }
}

 

Output:

Let's eat Fruits.
Mango is sweet.

We have an abstract class Fruits that has an abstract method taste() and a regular method eat(). We cannot directly create object of fruit class.

First, we inherit methods of the fruit class into the Mango class and access the abstract method through it.

Lastly, we create an object of the inherited class to use the abstract methods.

Thus we can see that the implementation of the class can be kept hidden from the end user.

 

ii. Interfaces

Interface in java is mainly used to achieve abstraction. We use the implements keyword to implement an interface. 

Example:

interface Fruits {
    public abstract void taste();
    public void eat();
}

class Mango extends Fruits {
    
    public void taste() {
        System.out.println("Mango is sweet.");
    }
    
    public void eat() {
        System.out.println("Let's eat Fruits.");
    }
}

public class Example4 {
    public static void main(String[] args) {
        Mango m = new Mango();
        m.eat();
        m.taste();
    }
}

 

Output:

Let's eat Fruits.
Mango is sweet.

As we can see, implementing an interface is not that different from creating and abstract class and method. So what is the main difference between an abstract class and an interface?

 

Abstract Class	Interface
abstract keyword is used to create abstract class.	Interface keyword is used to create an interface.
Abstract class is implemented using extends keyword.	Interface is implemented using implements keyword.
Can extend another class or interface.	Can only extend an interface.
Can provide implementation of interface.	Cannot provide implementation of interface.
Does not support multiple inheritance.	Supports multiple inheritance.
Has abstract and non-abstract methods.	Has default, static and abstract methods.