Abstract Class vs Interface Demo Example

Interface and Abstract Class are used for abstraction.

Keyword:

• An interface is preceded with keyword interface.
• An Abstract class is preceded with keyword abstract.

Access modifier:

• Data members in inteface are always public.
• Data members in abstract class can be private, protected, etc.

Accessibility:

• Data members in inteface are always static.
• Data members in abstract class can be static and non-static.

Type of Variable:

• Data members in inteface are always final.
• Data members in abstract class can be final and non-final.

Methods:

• Methods in interface are by default abstract and public, java 8 can have body to the methods.
• Abstract class can have both abstract and non-abstract methods.

Inheritance vs Abstraction:

• A class implements an interface.
• A class extends abstract class.

Multiple implementations:

• A class can implement more than one interface.
• A class cannot extend more than one class.

#My Notes:

Interfaces (100% abstraction)

• To be used needs to use impplements keyword.
• All variables are public static final
• Can only have abstract methods

Abstract Class

• To be used needs to use extends keyword.
• Can have abstract methdos (without body) and non-abstract mehtods (with body)
• Abstract class can not be initialized.

Usage:

If we know the implementations we can use Abstract Class, if we don't know the implementation it's better to use and interface.