What is the difference between Java abstract classes and interfaces?

#What is the difference between Java abstract class and interface?

Abstract class: In Java, a class modified by the abstract keyword is called an abstract class, and a method modified by the abstract keyword is called an abstract method. Abstract methods only have methods. Statement, there is no method body. Characteristics of abstract classes:

1. Abstract classes cannot be instantiated and can only be inherited;

2. Those that contain abstract methods must be abstract classes, but abstract classes do not necessarily contain abstract methods;

3. The modifier of an abstract method in an abstract class can only be public or protected, and the default is public;

4. If a subclass inherits an abstract class, the subclass must implement the parent Class abstract method, otherwise the subclass must also be defined as an abstract class;

5. Abstract classes can contain attributes, methods, and constructors, but constructors cannot be used for instantiation and are mainly used to be called by subclasses.

Interface: The interface in Java is modified with the interface keyword. The characteristics are:

1. The interface can contain variables and methods; the variable is designated as public static final by Hermit. The method is designated as public abstract by Hermit (before JDK1.8);

2. The interface supports multiple inheritance, that is, one interface can extend multiple interfaces, which indirectly solves the problem of single inheritance of classes in Java;

3. A class can implement multiple interfaces;

4. New features have been added to interfaces in JDK1.8:

• Default method (default method): JDK 1.8 allows adding non-abstract method implementations to interfaces, but they must be modified with the default keyword; the method that defines default does not need to be implemented by the implementation subclass, but can only be called by the object that implements the subclass; if the subclass If a class implements multiple interfaces, and these interfaces contain the same default method, the subclass must override the default method;

• static method: static method is allowed in JDK 1.8 The keyword modifies a method and provides an implementation, which is called an interface static method. Interface static methods can only be called through the interface (interface name. static method name).

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