🐷1.接口的概念

🐱‍🚀2.接口的语法规则

💚3.接口的使用

🚀4.接口的特性

🎆5.实现多个接口

🐶6.接口间的继承

🎊7.接口使用的实例

1.什么是接口呢？？？

接口放在现实生活中来说呢，就是手机啊。电脑的插座之类的，我们会发现那些插座几乎大家的充电口都能用，那么这就是一种标准

 接口不能直接实例化，会报错

interface IShape{public abstract void  draw();public static final String name="一宝";default   public    void func(){System.out.println("默认的");}}
class Rect implements IShape{@Overridepublic void draw() {System.out.println("🟥");}
}
class  Circle implements IShape{@Overridepublic void draw() {System.out.println("○");}
}
class  Heart implements IShape{@Overridepublic void draw() {System.out.println(";❤");}
}public class Test {public static void main(String[] args) {IShape shape = new Rect();IShape shape2 = new Circle();IShape shape3 = new Heart();shape.draw();shape.func();shape2.draw();shape2.func();shape3.draw();shape3.func();}}

 对于shape.func（）可以这样理解，调用shape.draw()发生动态绑定，就到那个Rect重写的draw方法去了，但是调用shape.fun（）就到接口中去了，因为func本身也是一个抽象方法，因为有了default的修饰，所以可以不在子类中重写，通过接口的引用，就直接到IShape当中去调了

下面实现电脑USB接口

package demo2;/*** Created with IntelliJ IDEA.* Description:* User: WHY* Date: 2022-11-16* Time: 10:52*/
interface  IUSB{void openDevice();void closeDevice();
}
class  KeyBoard implements IUSB  {@Overridepublic void openDevice() {System.out.println("打开键盘");}@Overridepublic void closeDevice() {System.out.println("关闭键盘");}public void intput(){System.out.println("敲击键盘");}
}
class   Mouse implements IUSB{@Overridepublic void openDevice() {System.out.println("打开鼠标");}@Overridepublic void closeDevice() {System.out.println("关闭鼠标");}public void click(){System.out.println("点击鼠标");}
}
class Computer{public void open(){System.out.println("开机");}public void close(){System.out.println("关机");}public void useDevice(IUSB  usb){//判断一下是不是所有的USB接口都可以被使用usb.openDevice();if(usb instanceof Mouse){Mouse mouse=(Mouse)usb;//向下转型mouse.click();//执行子类中特有的方法}else if(usb instanceof KeyBoard){KeyBoard keyBoard=(KeyBoard)usb;keyBoard.intput();}usb.closeDevice();}
}public class Test {public static void main(String[] args) {Computer computer=new Computer();IUSB  iusb=new KeyBoard();//向上转型computer.useDevice(iusb);IUSB iusb1=new Mouse();computer.useDevice(iusb1);}}

package demo3;/*** Created with IntelliJ IDEA.* Description:* User: WHY* Date: 2022-11-16* Time: 13:48*/
abstract class Animal{public String name;public Animal(String name) {this.name = name;}
}
interface IRunning{void run();
}
interface ISwimming{void swim();
}
interface IFly{void fly();
}
class Dog extends Animal  implements  IRunning{public Dog(String name) {super(name);}@Overridepublic void run() {System.out.println(name+"正在跑");}}
class Duck extends Animal implements  IFly,IRunning,ISwimming{public Duck(String name) {super(name);}@Overridepublic void run() {System.out.println(name+"正在跑");}@Overridepublic void fly() {System.out.println(name+"正在飞");}@Overridepublic void swim() {System.out.println(name+"正在游泳");}
}
class  robot implements ISwimming{public String name;public robot(String name) {this.name = name;}@Overridepublic void swim() {System.out.println(name+"机器人在游泳");}
}public class TestDemo {public static void walk(IRunning iRunning){iRunning.run();}public static void swim(ISwimming iSwimming){iSwimming.swim();}public static void main(String[] args) {walk(new Dog("贝贝"));walk(new Duck("丫丫"));swim(new Duck("丫丫1"));swim(new robot("小冰"));}}

从这两段代码可以看出，只要这个类继承了这个接口，就可以实现

package demo4;/*** Created with IntelliJ IDEA.* Description:* User: WHY* Date: 2022-11-16* Time: 14:14*/
class Student  implements Comparable{public String name;public int age;public int score;public Student(String name, int age, int score) {this.name = name;this.age = age;this.score = score;}@Overridepublic String toString() {return "Student{" +"name='" + name + '\'' +", age=" + age +", score=" + score +'}';}public int compareTo(Student o){//根据年龄比较排序if(this.age>o.age){return 1;}else if(this.age 0) {return 1;}else if(this.name.compareTo(o.name) < 0) {return -1;}else {return 0;}*/
//使用冒泡排序实现依据年龄排序
public class Test {public static void sort(Comparable[] array) {for (int i = 0; i < array.length-1; i++) {for (int j = 0; j < array.length-1-i; j++) {/*if(array[j] > array[j+1]) {交换；}*/if(array[j].compareTo(array[j+1]) > 0) {Comparable tmp = array[j];array[j] = array[j+1];array[j+1] = tmp;}}}}public static void main(String[] args) {Student[]  students=new Student[3];students[0]=new Student("wangyibo",25,100);students[1]=new Student("weihongyan",19,99);students[2]=new Student("gaoyan",19,95);System.out.println(students[0].compareTo(students[1]));}}

 这个是调用sort函数实现排序

这个是调用compareTo方法实现的

当比较字符串是否相等用equals方法，当比较大小也要用compareT方法，要是想从大到小排，换个return  就好

 下面来总结一下接口的知识点

使用interface 接口来定义接口

接口不能被实例化

接口中的方法默认是public abstract 修饰的

接口中的成员默认是public static  final  修饰的

接口当中的方法，不能有具体实现，但是从jdk8开始，可以写一个default来修饰，我已经子啊前面的代码展示并解释了

接口当中不能有构造方法

接口需要被类实现，使用关键字implements

接口中可以有static修饰的方法

接口和接口之间使用关键字extends继承，与类的单继承不一样啊，类可以同时继承多个接口，接口和接口之间也可以多继承

interface A {void funcA();}
interface B {void funcB();
}
//CC这个接口 不仅仅具备func这个功能，还具备了A和B接口的功能
interface CC extends A,B {void funcC();
}class C implements CC {public void funcA() {}public void funcB() {}public void funcC() {}}
public class Test2 {
}

就像这个，一个接口也可以同时继承多个接口，并拥有被继承接口的功能

类继承另一个类同时实现多个接口，代码也有体现到

今天的内容就到此结束，我们下期再见，886！！！

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