An Abstract class has abstract methods. An Abtsract class can not be instanitiated directly. All the abtract methods are implemented in the derived class. There is no multiple inheritance here.

Interface class also has abstract methods and all of them are public. You can have multiple inheritance with Interfaces.

Ans:

In an interface class all methods are abstract - there is no implementation. In an abstract class some methods can be concrete. In an interface class no accessibility modifiers are allowed. An abstract class may have accessibility modifiers.

Interface :

1. All the methods in the interface are abstract.
2. We can achieve multiple inheritance through interface.
3. All the methods in the interface should be without Access modifier. Implicitly public.

Abstract class:

1. Abstract class may contain abstract method and non-abstract method.
2. We can achieve only single inheritance and multi-level inheritance.
3. Abstract methods have Access modifiers.

An Interface is created/used when we have different types of objects while an abstract class is used when there is a single root hierarchy.

Abstarct class is like normal class with 2 specials. 1. It can not be instanciated 2. It can have abstarct functions. Abstract class is used in inheritance as super class where some common implementation is requried.

Example is Thread class

interface is different type than class. All the members are public and no implementation is allowed. Interfaces are used for 1. For declaring project level constants because all variables public final and static. 2. In delegation pattern for providing flexibilty of implementation.

Example is runnable interface

Abstract class:

1. Abstract class may contain abstract method and concrete method(means having own implemantion).
2. Abstract methods have Access modifiers(Public protected internal etc).

Interface :

1. All the methods in the interface are abstract.
2. We can achieve multiple inheritance through interface.
3. Donot have access Modifiers by default is PUBLIC

Interface

All methods are abstract and there is no implementation.

No access modifiers are allowed.

Interfaces are essentially having all method prototypes no definition

We can achieve multiple inheritance through interface

Abstract class

Some methods can be concrete.

They have access modifiers

Contain method definitions also.

We can achieve only single inheritance and multi-level inheritance

It can not be instantiated