Difference between an abstract class and interface in Java

Another commonly asked interview question is to explain the difference between an abstract class and an interface. So in this blog post, I will give you a detailed explanation.

What is an Abstract Class?

An abstract class is a class that has one or more abstract method. An abstract method is a method that has the “abstract” keyword specified in the method definition. It does not have any method body, it is up to the subclass of the abstract class to provide an implementation for the abstract method.

So why is an abstract class useful?

Sometimes, you will want to create a super class that defines a method that all its sub classes must implement, but it leaves the exact implementation to the sub class. For ex. suppose you have a class called Shape, you can define an abstract method called draw. You can then have sub-classes for various shapes like Rectangle, Triangle, etc which provide implementations for the draw method. So while the “draw” method makes no sense for the Shape class, it makes sense for the Rectangle and Triangle classes and so it makes sense to have the code for the draw me

What is an Interface?

An interface is a java construct that specifies methods without any method bodies. The code for the methods within the interface must be provided by the classes that implement the interface.

Why is an interface useful?

Using  an interface, you can specify what a class must do, but not how it does it.   So you can use it to specify a behavior that classes must implement.

So what are the similarities between abstract class and interface?

  • Both abstract classes and interfaces are used to specify a behavior
  • Both cannot be instantiated

How are they different?

Edit
Abstract ClassInterface
An abstract class can have non-abstract methods i.e. methods with method bodiesAll methods within the interface are abstract so it cannot have methods with method bodies.
Only one class can extend an abstract classAn interface can be implemented by several classes
An abstract class can have protected and public abstract methodsAn interface can have only have public abstract methods
Can have instance variablesCannot have instance variables, all variables are implicitly static and final since an interface cannot be instanitated
Can have a constructorCannot have constructors

When to use which?

An abstract class should be used when you want methods in the base class to have some basic default behavior but want to leave it to the subclasses to override these methods. An interface should be used when you want to define a behavior that other classes (probably external) must implement.

 

Comments

Post a Comment

Popular posts from this blog

How to use logging in SpringBoot with code samples

Image
In this article, we will learn how to use logging in SpringBoot. Introduction There are several Java logging frameworks like logback, log4j, and so on. Spring Boot supports out-of-the-box support for logback. Let us learn how to use logging in SpringBoot with logback. Step 1 – Create a New Maven Project Create a new Maven project. (Refer to  this  blog post). This will create a project in Eclipse as follows:   Step 2 – Add the Spring Boot Dependencies Add the spring-boot-starter-web dependency to the pom.xml . So, the pom.xml should look as follows: <project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd"> <modelVersion>4.0.0</modelVersion> <groupId>com.learnjava</groupId> <artifactId>learnjava-springboot-logging-example</artifactId> <version>0.0.1-SNAPSHOT&
Read more

Python While Loop with code samples

Much like a Java while loop, you can use a Python while loop to repeatedly execute a block of code as long as a condition is true. In this article, we will learn more about the Python while loop. Python While loop Syntax A while loop in Python has the following syntax: while <condition>: loop body The while keyword is followed by a condition. If the condition evaluates to true, the body of the loop is executed. Once the body of the loop is completed, the condition is checked again and this is repeated until the condition evaluates to false at which point the loop is exited. While loop Sample Code The following code demonstrates how you can use the while loop: num=10counter=1total=0while counter<=num: total += counter counter+=1print("sum of first 10 numbers is",total) This code adds the numbers from 1 to 10 and prints the sum. It uses a while loop to iterate from 1 to 10. The while loop checks the condition counter <= num and if so adds the current value of count
Read more

How to convert a List to a Set

In this blog post ,I will be showing you how you can convert a List to a Set. Consider the following code snippet: public class ListToSetDemo {public static void main(String[] args) {List<Integer> list = Arrays.asList(5,3,11,15,9);//Method 1Set<Integer> set = new HashSet<Integer>(list);System.out.println("Set is "+set);//method 2Set<Integer> set2 = new HashSet<Integer>();set2.addAll(list);System.out.println("Set is "+set2);}} This code demonstrates two ways to convert a List to a Set. Method 1 Here, we are creating a new HashSet . We are invoking the constructor that accepts a Collection object. Here, we are passing in the input list to this constructor.   Method 2 Here again, we are creating a new HashSet . However, we are using the default constructor. We are then invoking the addAll method and passing in the input list.   When you run this code, it will print the following output: Set is [3, 5, 9, 11, 15]Set is [3, 5, 9, 11, 15] No
Read more