# Interface Vs Abstract Class In Java - Did You Know What's The Difference? **URL:** \ **Category:** Tutorials & Methods\ **Tags:** tools, programming, tips-tricks\ **Created:** [September 15, 2019, 8:39pm UTC](https://onehack.st/t/interface-vs-abstract-class-in-java-did-you-know-whats-the-difference/57665 "2019-09-15T20:39:00Z")\ **Posts on this page:** 2\ **Page:** 1
**Author:** ![Aina](https://onehack.st/user_avatar/onehack.st/aina/32/167469_2.png) [@Aina](https://onehack.st/u/Aina)\ **Post date:** [September 15, 2019, 8:39pm UTC](https://onehack.st/t/interface-vs-abstract-class-in-java-did-you-know-whats-the-difference/57665/1 "2019-09-15T20:39:01Z")
## What is Interface? The interface is a blueprint that can be used to implement a class. The interface does not contain any concrete methods (methods that have code). All the methods of an interface are abstract methods. _(Source: Guru99)_ An interface cannot be instantiated. However, classes that implement interfaces can be instantiated. Interfaces never contain instance variables but, they can contain public static final variables (i.e., constant class variables) ## What Is Abstract Class? A class which has the abstract keyword in its declaration is called abstract class. Abstract classes should have at least one abstract method. , i.e., methods without a body. It can have multiple concrete methods. Abstract classes allow you to create blueprints for concrete classes. But the inheriting class should implement the abstract method. Abstract classes cannot be instantiated. **Important Reasons For Using Interfaces** - Interfaces are used to achieve abstraction. - Designed to support dynamic method resolution at run time - It helps you to achieve loose coupling. - Allows you to separate the definition of a method from the inheritance hierarchy **Important Reasons For Using Abstract Class** - Abstract classes offer default functionality for the subclasses. - Provides a template for future specific classes - Helps you to define a common interface for its subclasses - Abstract class allows code reusability. ## Interface Vs. Abstract Class | **Parameters** | **Interface** | **Abstract class** | | --- | --- | --- | | Speed | Slow | Fast | | Multiple Inheritances | Implement several Interfaces | Only one abstract class | | Structure | Abstract methods | Abstract & concrete methods | | When to use | Future enhancement | To avoid independence | | Inheritance/ Implementation | A Class can implement multiple interfaces | The class can inherit only one Abstract Class | | Default Implementation | While adding new stuff to the interface, it is a nightmare to find all the implementors and implement newly defined stuff. | In case of Abstract Class, you can take advantage of the default implementation. | | Access Modifiers | The interface does not have access modifiers. Everything defined inside the interface is assumed public modifier. | Abstract Class can have an access modifier. | | When to use | It is better to use interface when various implementations share only method signature. Polymorphic hierarchy of value types. | It should be used when various implementations of the same kind share a common behavior. | | Data fields | the interface cannot contain data fields. | the class can have data fields. | | Multiple Inheritance Default | A class may implement numerous interfaces. | A class inherits only one abstract class. | | Implementation | An interface is abstract so that it can’t provide any code. | An abstract class can give complete, default code which should be overridden. | | Use of Access modifiers | You cannot use access modifiers for the method, properties, etc. | You can use an abstract class which contains access modifiers. | | Usage | Interfaces help to define the peripheral abilities of a class. | An abstract class defines the identity of a class. | | Defined fields | No fields can be defined | An abstract class allows you to define both fields and constants | | Inheritance | An interface can inherit multiple interfaces but cannot inherit a class. | An abstract class can inherit a class and multiple interfaces. | | Constructor or destructors | An interface cannot declare constructors or destructors. | An abstract class can declare constructors and destructors. | | Limit of Extensions | It can extend any number of interfaces. | It can extend only one class or one abstract class at a time. | | Abstract keyword | In an abstract interface keyword, is optional for declaring a method as an abstract. | In an abstract class, the abstract keyword is compulsory for declaring a method as an abstract. | | Class type | An interface can have only public abstract methods. | An abstract class has protected and public abstract methods. | ## Sample code for Interface and Abstract Class in Java Following is sample code to create an interface and abstract class in Java **Interface Syntax** ```auto interface name{ //methods } ``` **Java Interface Example:** ```auto interface Pet { public void test(); } class Dog implements Pet { public void test() { System.out.println("Interface Method Implemented"); } public static void main(String args[]) { Pet p = new Dog(); p.test(); } } ``` **Abstract Class Syntax** ```auto abstract class name{ // code } ``` **Abstract class example:** ```auto abstract class Shape { int b = 20; abstract public void calculateArea(); } public class Rectangle extends Shape { public static void main(String args[]) { Rectangle obj = new Rectangle(); obj.b = 200; obj.calculateArea(); } public void calculateArea() { System.out.println("Area is " + (obj.b * obj.b)); } } ``` ## ENJOY & HAPPY LEARNING! 👍 ---
**Author:** ![E10n](https://onehack.st/user_avatar/onehack.st/e10n/32/22265_2.png) [@E10n](https://onehack.st/u/E10n)\ **Post date:** [September 15, 2019, 8:55pm UTC](https://onehack.st/t/interface-vs-abstract-class-in-java-did-you-know-whats-the-difference/57665/2 "2019-09-15T20:55:07Z")
@Aina thanks for all the knowledge ❤