What does the interface do?

The role of interfaces: 1. Interfaces can separate projects, and all layers are developed towards interfaces, improving development efficiency; 2. Interfaces reduce the coupling between code and code; 3. Interfaces can be implemented in multiple ways, Multiple inheritance, and in addition to interfaces, a class can also inherit other classes.

The role of the interface:

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1. Projects can be separated, and all layers are developed for interfaces to improve development efficiency;

2. The interface reduces the coupling between code and code, becomes pluggable, and can be switched at will;

3. Both interfaces and abstract classes can complete a certain function. Interfaces are preferred because interfaces can be implemented and inherited in multiple ways, and in addition to interfaces, a class can also inherit other classes.

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Code sample:

public interface CustomerService {    //定义一个推出系统的方法
    void logout();
}

package date818;//接口实现类1public class CustomerServierImpl implements CustomerService {    
    public void logout(){
        System.out.println("成功退出系统");
    }
}

package date818;//接口实现类2public class CustomerServiceImpl2 implements CustomerService{    
    public void logout(){
        System.out.println("hello world");
    }
}

package date818;public class TestCustomer {    
    public static void main(String[] args){  //需要执行CustomerServiceImpl和CustomerImpl2接口实现类中的logout方法
        //以下程序面向接口调用
        CustomerService cs = new CustomerServierImpl();//多态。父类型引用指向子类型对象
        //调用
        cs.logout();
        CustomerService cs2 = new CustomerServiceImpl2();
        cs2.logout();
    }
}

Define interface

package date818;
public interface Engine {    //所有发动机都可以通过这个接口启动
    void start();
}//定义实现接口的类
package date818;
public class Honda implements Engine{    
    public void start(){
        System.out.println("本田启动");
    }
}
package date818;public class Ymaha implements Engine{    
    public void start(){
        System.out.println("雅马哈启动");
    }
}//定义生产汽车的类package date818;public class Car {    //面向接口编程，不能将类实例化
    /**
     * 引用接口定义一个属性e，相当于
     * String name;
     * Integer age;
     * 类里定义的变量是成员变量；方法里定义的变量是局部变量。
     */
    Engine e ;//成员变量e

    Car(Engine e){        //定义构造方法，把局部变量e赋值给成员变量
        this.e=e;
    }    //对外提供的测试方法
    public void testEngine(){        //成员变量e
        e.start();
    }
}//定义测试类package date818;public class TestCar {    
    public static void main(String[] args){        //生产引擎
        Engine e = new Ymaha();        //根据构造方法传入参数生产汽车
        Car c = new Car(e);        //测试引擎
        c.testEngine();

        c.e = new Honda();//已经定义了一个实例，直接对实例的参数修改即可
        c.testEngine();
    }
}

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