What is the difference between abstract class and interface in java?

In Java, abstract classes and interfaces are both used to achieve abstraction, so what is the difference between them? The following article will introduce it to you. It has certain reference value. Friends in need can refer to it. I hope it will be helpful to everyone.

Abstract class

Abstract class is used to capture the common characteristics of subclasses, that is, what they have in common; for example: cars, Bicycles and electric scooters are all cars and can have a common abstract class: Vehicle. Abstract classes cannot be instantiated, cannot be used to create objects, and can only be used as superclasses for subclasses.

Interface

An interface is a collection of abstract methods. If a class implements an interface, then it inherits all the abstract methods of this interface.

Note: An abstract method is a special method that has only declarations but no specific implementation.

The interface is just a form, it cannot do anything by itself; if you want to implement an interface, you must make sure to implement all the methods in this interface.

The difference between abstract classes and interfaces:

1. An abstract class can have both abstract and concrete methods; while an interface can only have abstract methods, which are abstract methods Collection of (starting from Java 8, it can also have default and static methods).

2. Abstract classes do not support multiple inheritance. You can only extend one class or one abstract class at a time. Interfaces support multiple inheritance and any number of interfaces can be extended at one time.

3. Abstract classes can have final, non-final, static and non-static variables. Interfaces only have static and final variables.

4. An abstract class can extend another concrete (regular) class or abstract class and implement one or more Java interfaces. An interface can only extend another Java interface, and interfaces cannot implement abstract classes.

5. In an abstract class, the keyword: "abstract" is required to declare a method as abstract. In the interface, the keyword: "abstract" is optional and is used to declare the method as abstract

7. You can use the keyword "extends" to extend the abstract class. An interface class can be implemented using the keyword "implements".

8. Java abstract classes can have protected and public abstract methods, and can have class members, such as private, protected, etc. By default, the members of a Java interface are public, and an interface can only have public abstract methods.

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