Basic syntax and definition of Java interface classes

Basic syntax and definition methods of Java interface classes

In Java programming, an interface (Interface) is a special class used to define a set of methods Specification, but does not provide specific implementation. Interface classes play an important role in code design, helping to implement code modularization and providing flexible extensibility and polymorphism. This article will introduce the basic syntax and definition method of interface classes, with specific code examples.

1. Declaration and definition of interface class
In Java, you can use the keyword "interface" to declare and define an interface class. An interface class is an abstract class that cannot be instantiated and can only be used by classes that implement the interface.

The syntax of the interface class is as follows:

public interface 接口名 {
    // 定义接口方法
    方法返回类型 方法名(参数列表);
    // ...
}

2. Characteristics and precautions of the interface class

1. The methods defined in the interface class default It is an abstract method and does not contain specific implementation content, only the method signature. Therefore, the "abstract" keyword cannot be used to modify methods in interface classes.
2. Constants can be defined in interface classes, but ordinary variables and instance methods cannot be included.
3. A class can implement one or more interface classes and are associated through the "implements" keyword.
4. The class that implements the interface class must implement all abstract methods in the interface class, otherwise the class needs to be declared as an abstract class.
5. Methods in interface classes are public by default, that is, using the "public" modifier, they can be accessed directly through the interface name.

3. Example of definition of interface class
The following uses an example to specifically illustrate the definition and use of interface class.

Define an interface class (Animal.java):

public interface Animal {
    // 声明抽象方法
    void eat();

    void sleep();
}

Implement the interface class (Cat.java):

public class Cat implements Animal {
    // 实现接口中的抽象方法
    @Override
    public void eat() {
        System.out.println("Cat is eating.");
    }

    @Override
    public void sleep() {
        System.out.println("Cat is sleeping.");
    }
} 

Implementation interface class (Dog.java):

public class Dog implements Animal {
    // 实现接口中的抽象方法
    @Override
    public void eat() {
        System.out.println("Dog is eating.");
    }

    @Override
    public void sleep() {
        System.out.println("Dog is sleeping.");
    }
} 

Test class (Main.java):

public class Main {
    public static void main(String[] args) {
        Animal cat = new Cat();    // 定义一个接口类对象
        Animal dog = new Dog();    // 定义一个接口类对象

        cat.eat();    // 调用接口方法
        cat.sleep();

        dog.eat();
        dog.sleep();
    }
}

Program running results ：

Cat is eating.
Cat is sleeping.
Dog is eating.
Dog is sleeping.

In the above example, we defined an interface class Animal, and implemented the abstract methods in the interface in the implementation classes Cat and Dog. By creating an object of the interface class and calling the corresponding method, the specific function is completed.

To sum up, this article introduces the basic syntax and definition method of Java interface classes in detail, including the declaration and definition of interfaces, characteristics and precautions, and demonstrates the use of interface classes through sample code. Interface classes are widely used in Java programming. They can provide code modularization and flexible scalability, and bring a lot of convenience to our programming work.

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