>> Abstract Class VS Interface

Abstract Class VS Interface

To read about Interface  click here

To read about Abstract Class click here

While creating interface , you create it as interface. While creating abstract class, you create it as regular class and later you convert it as an abstract class.

Abstract class have keyword "abstract class" , Interface has keyword "interface".

Abstract methods inside Abstract class should use the keyword "abstract". Abstract method inside interface may or may not use "abstract" keyword.

Access modifiers for the interface variables and methods are by default public. It allows public and default only.

Access modifiers for an abstract class variables and methods are private(only non-abstract methods and variables), public or  protected.

Interface can have only abstract methods.

Abstract class can have both abstract and non-abstract methods and constructors.

The variables values in interface are final by default.

The variables values in abstract methods need not to be final.

An abstract class can extend another abstract class or implement interface.

An interface can not extend any classes. Interface can extend another interface or interfaces.

An abstract class or normal class can not extend more than one abstract class or normal class , ie, does not support multiple inheritance.

An interface can extend one or more interfaces. An abstract class or normal class can implements one or more interfaces.

public interface InterfaceName extends Intf1, Intf2{  

      

}

public class ClassName implements Intf1, Intf2 {  //class or abstract class

}

Speed wise Interface is slow, Abstract class is fast.

Default access modifier is possible only in interface. Because in an existing interface, the abstract methods are already being implemented by implementing classes. So, if you add any other regular abstract method, those implementing classes have to implement them. To avoid this situation, we use default access modifier to write new method in interface.

public interface InterfaceXYZ {

       default void red() {

              System.out.println("Default method in interface");

       }

Class implementing the interface:

public class XYZ implements InterfaceXYZ{

       public static void main(String[] args) {

             

              XYZ xyz = new XYZ();

              xyz.red();       

       }

Output:

Default method in interface

Benefits of Interface and Abstract Class :

Interface and Abstract class are used mainly for security (hiding data/information). Other benefits of using Abstract Class(AC) are : AC is faster, it allows different access modifiers , it allows abstract and non-abstract methods, it can implements more than one interfaces, variables could be final, non-final, static, non-static , initialized , non-initialized , AC can have constructors.

Benefits of Interface: Security, allows default access modifier , allows multiple inheritance.