Compare interface inheritance and multiple inheritance in Java

Comparison of interface inheritance and multiple inheritance in Java

In Java, an interface is an abstract type that defines methods and constants. Interfaces can be implemented by classes, and a class can implement multiple interfaces. In the implementation of interfaces, there are two methods: interface inheritance and multiple inheritance. This article will discuss the differences between the two methods and give specific code examples to deepen understanding.

1. Inheritance of interface

Inheritance of interface means that one interface can inherit from another interface, and the methods and constants in the inherited interface will also be inherited. Interface inheritance uses the keyword extends to inherit one or more interfaces. Here is a sample code for interface inheritance:

public interface Animal {
    void eat();
    void sleep();
}

public interface Dog extends Animal {
    void bark();
}

In the above code, interface Dog inherits interface Animal, so Dog interface In addition to containing its own method bark(), it also inherits the methods eat() and sleep() of the Animal interface. Classes that implement the Dog interface need to implement not only the bark() method, but also the eat() and sleep() methods.

2. Multiple inheritance

Multiple inheritance means that a class can inherit multiple interfaces at the same time. Different from the inheritance of interfaces, a class in Java can only inherit one class, but can implement multiple interfaces. Here is a sample code for multiple inheritance:

public interface Flyable {
    void fly();
}

public interface Swimmable {
    void swim();
}

public class Bird implements Flyable, Swimmable {
    @Override
    public void fly() {
        System.out.println("Bird is flying.");
    }

    @Override
    public void swim() {
        System.out.println("Bird is swimming.");
    }
}

In the above code, the class Bird implements the interfaces Flyable and Swimmable, so The Bird class needs to implement the methods fly() and swim() declared in the interface. By implementing multiple interfaces, the Bird class can have the ability to fly and swim at the same time.

3. Comparison between interface inheritance and multiple inheritance

The biggest difference between interface inheritance and multiple inheritance is the difference in semantics. Interface inheritance is a way to extend or add functions. The inherited interfaces are related and belong to related functions in the same field. Multiple inheritance is a way to achieve multiple functions, in which the inherited interfaces can come from different fields and have no direct correlation.

In addition, interface inheritance can be used to organize the structure of the code and classify similar functions. Through inheritance relationships, interface extension and layering can be achieved, making the code clearer and easier to maintain. Multiple inheritance is often used when multiple functions need to be implemented, and different capabilities are obtained by implementing multiple interfaces.

It is worth noting that a class in Java can only inherit one class, but can implement multiple interfaces. This design is to solve the problems caused by multiple inheritance, such as diamond inheritance problem and method conflict problem.

In summary, interface inheritance and multiple inheritance have different semantics and application scenarios in Java. Inheritance of interfaces is suitable for extending and classifying related functions, while multiple inheritance is suitable for implementing multiple functions. Through flexible use of interface inheritance and multiple inheritance, the code can be made clearer, more logically structured, and richer in functionality.

Reference:

• Oracle. The Java™ Tutorials - Interfaces.（https://docs.oracle.com/javase/tutorial/java/IandI/index.html）

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