Difference Between Abstract Class and Interface

An abstract class permits you to make functionality that subclasses can implement or override whereas an interface only permits you to state functionality but not to implement it. A class can extend only one abstract class while a class can implement multiple interfaces.

1. What is the difference between an abstract class and an interface and when would you use one over the other?
2. What is difference between abstract class and interface after Java 8?
3. What is the difference between abstract class and interface till Java 7?
4. Where do we use abstract class?
5. When would you use an abstract class instead of an interface?
6. Can we override static method?
7. Can abstract class have constructor?
8. Can an abstract class implement an interface?
9. What is difference between class and interface?
10. Can we instantiate abstract class?
11. What is abstract class example?

What is the difference between an abstract class and an interface and when would you use one over the other?

The short answer: An abstract class allows you to create functionality that subclasses can implement or override. An interface only allows you to define functionality, not implement it. And whereas a class can extend only one abstract class, it can take advantage of multiple interfaces.

What is difference between abstract class and interface after Java 8?

The differences it highlights are the accessibility of data members and methods: abstract classes allow non-static and non-final fields and allow methods to be public, private, or protected while interfaces' fields are inherently public, static, and final, and all interface methods are inherently public.

What is the difference between abstract class and interface till Java 7?

Abstract classes can have both abstract methods as well as methods with implementation. Interfaces, till Java 7, could only have public abstract methods. ... Abstract classes can have fields that are not static and final. In interfaces, all fields are automatically public, static, and final and used to define constants.

Where do we use abstract class?

When to use an abstract class

• An abstract class is a good choice if we are using the inheritance concept since it provides a common base class implementation to derived classes.
• An abstract class is also good if we want to declare non-public members. ...
• If we want to add new methods in the future, then an abstract class is a better choice.

When would you use an abstract class instead of an interface?

Abstract classes should be used primarily for objects that are closely related, whereas interfaces are best suited for providing common functionality to unrelated classes. If you are designing small, concise bits of functionality, use interfaces. If you are designing large functional units, use an abstract class.

Can we override static method?

Can we Override static methods in java? We can declare static methods with the same signature in the subclass, but it is not considered overriding as there won't be any run-time polymorphism. Hence the answer is 'No'.

Can abstract class have constructor?

The constructor inside the abstract class can only be called during constructor chaining i.e. when we create an instance of sub-classes. This is also one of the reasons abstract class can have a constructor.

Can an abstract class implement an interface?

In Java, an abstract class can implement an interface, and not provide implementations of all of the interface's methods. It is the responsibility of the first concrete class that has that abstract class as an ancestor to implement all of the methods in the interface.

What is difference between class and interface?

A class describes the attributes and behaviors of an object. An interface contains behaviors that a class implements. A class may contain abstract methods, concrete methods. An interface contains only abstract methods.

Can we instantiate abstract class?

Abstract classes cannot be instantiated, but they can be subclassed. When an abstract class is subclassed, the subclass usually provides implementations for all of the abstract methods in its parent class.

What is abstract class example?

A class that is declared using “abstract” keyword is known as abstract class. It can have abstract methods(methods without body) as well as concrete methods (regular methods with body). A normal class(non-abstract class) cannot have abstract methods.