Abstraction in Java

In Java abstraction is the technique which we come across every day. Abstraction is one of the major pillars of OOP. Using abstraction we can achieve great things. Today in this article we are going to discuss abstraction. Let’s understand what abstraction is.

What is abstraction?

Abstraction is related to data/details. Data abstraction is the process of hiding details from the user and showing only the necessary information. This mechanism helps the developer to hide trivial information from the user. For instance: the user will see the ATM as an ATM rather than its components.

Let us understand this by taking the real-life scenario of an ATM. While using the ATM the user only knows that by pressing the “Withdraw Cash” button he will get the cash or by pressing the “Get Statement” he will get the bank statement. The user is completely unaware of how the cash is withdrawn, what calculation the ATM did to withdraw the cash or how the bank statement is calculated.

Now that we have the upper level of knowledge on what exactly the abstraction is, let's discuss this topic in terms of java.

 

Abstraction in java

In java abstraction can be achieved using the interface and abstract classes. We can achieve 100% abstraction using interfaces in java.

There are abstract classes and abstract methods in java.

Abstract Classes:

          These are the restricted classes that cannot be used to create objects. It only contains abstract methods.

Abstract Methods:

       1. An abstract class is declared with abstract keyword.

       2. Abstract methods are those methods which are only declared they are not defined.

       3. An abstract class is a class which contains only abstract methods in it.

       4. An abstract class may or may not have abstract methods. Some of the methods in abstract class can be concrete methods also.

       5. Methods declared as an abstract need to be implemented in the sub-class thus making overriding compulsory or make the subclass as abstract.

       6. If a class contains one or more abstract methods then that class must be declared as Abstract.

       7. We cannot create the object of an Abstract class.

      8. The an abstract class can have parameterized constructor. A default constructor is always present in the abstract class.

 

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Where to use abstract class and abstract methods

There are situations where you want to define a superclass that declares an abstract structure without fully implementing each method. That is, sometimes we want to create a superclass that only defines the generalization form, which is shared by all its subclasses, leaving each subclass to fill out the description.

Consider the Person class example. Here the base type is Person and each person will have colour, height, weight and so on. From this specific type of person are derived Person1 and Person2, each of which will have specific characters.

            

Java program to illustrate the concept of Abstraction

	abstract class Person
	{
	// these are abstract methods
	String name;
	abstract String color();
	public abstract Long height();
	public abstract Long weight();
	// abstract class can have constructor
	public Person(String name) {
	System.out.println("Person constructor called");
	this. name = name;
	}
	// this is a concrete method
	public String getName() {
	return name;
	}
	}
	class Person1 extends Person
	{
	String name;
	public Person1(String name) {
	// calling Person constructor
	super(name);
	System.out.println("Person1 constructor called");
	this. name = name;
	}
	@Override
	String color() {
	System.out.println("Person1 colour is white");
	}
	@Override
	public Long weight() {
	return 65L;
	}
	@Override
	public Long height() {
	return 165L;
	}
	}
	class Person2 extends Person{
	String name;
	public Person2(String name) {
	// calling Person constructor
	super(name);
	System.out.println("Person2 constructor called");
	this. name = name;
	}
	@Override
	public Long weight() {
	return 50L;
	}
	@Override
	public Long height() {
	return 150L;
	}
	public class Test
	{
	public static void main(String[] args)
	{
	Person p1 = new Person1("Ram");
	Person p2 = new Person2("Shyam");
	System.out.println(p1.toString());
	System.out.println(p2.toString());
	}
	}
	}

view raw Abstraction hosted with ❤ by GitHub

Output:

Person constructor called.

Person1 constructor called.

Person constructor called.

Person2 constructor called.

Person1 weight is 65.

Person1 height is 165.

Person1 weight is 50

Person2 height is 150.

 

Advantages of Abstraction:

1.      It increases the reusability of code.

2.      It helps to increase the security as it exposes only the important functionalities of the application.

 

Related Articles:

        1.      Core java interview questions.

        2.      Java8 interview questions.

        3.      Internal working of Hashmap in java.

        4.   Encapsulation in java.

        5.      Compile time polymorphism in java.

        6.    Runtime Polymorphism in java.