IGNOU BCA 4th sem Solved Assignment - Differentiate Abstract class and Interface

Differentiate Abstract class and Interface

Ans

Features                                      Interfaces                                abstract class

Multiple inheritance	A class may inherit several interfaces.	A class may inherit only one abstract class.
Default implementation	An interface cannot provide any code, just the signature.	An abstract class can provide complete, default code and/or just the details that have to be overridden.
Access Modfiers	An interface cannot have access modifiers for the subs, functions, properties etc everything is assumed as public	An abstract class can contain access modifiers for the subs, functions, properties
Core VS Peripheral	Interfaces are used to define the peripheral abilities of a class. In other words both Human and Vehicle can inherit from a IMovable interface.	An abstract class defines the core identity of a class and there it is used for objects of the same type.
Homogeneity	If various implementations only share method signatures then it is better to use Interfaces.	If various implementations are of the same kind and use common behaviour or status then abstract class is better to use.
Speed	Requires more time to find the actual method in the corresponding classes.	Fast

1. Main difference is methods of a Java interface are implicitly abstract and cannot have implementations. A Java abstract class can have instance methods that implements a default behavior.

1. Variables declared in a Java interface is by default final. An  abstract class may contain non-final variables.

1. Members of a Java interface are public by default. A Java abstract class can have the usual flavors of class members like private, protected, etc..

1. Java interface should be implemented using keyword “implements”; A Java abstract class should be extended using keyword “extends”.

1. An interface can extend another Java interface only, an abstract class can extend another Java class and implement multiple Java interfaces.

1. A Java class can implement multiple interfaces but it can extend only one abstract class.

1. Interface is absolutely abstract and cannot be instantiated; A Java abstract class also cannot be instantiated, but can be invoked if a main() exists.

In comparison with java abstract classes, java interfaces are slow as it requires extra indirection.