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Java三大特性之接口

Java三大特性之接口

作者: Java编程日记 | 来源:发表于2022-04-07 16:40 被阅读0次

    前两篇文章，我们给大家分别介绍了Java三大特性中的前两个特性—— 继承 与 多态 。本文给大家介绍的是这三大特性中的最后一个—— 接口， 并且给大家通过一个综合案例加以说明。首先给大家介绍接口的相关基本概念。

    1.接口

    1.1接口的概述

    接口就是一种公共的规范标准，只要符合规范标准，大家都可以通用。 Java中的接口更多的体现在对行为的抽象！

    1.2接口的特点

    • 接口用关键字 **interface** 修饰

    <pre class="prettyprint hljs kotlin" style="padding: 0.5em; font-family: Menlo, Monaco, Consolas, "Courier New", monospace; color: rgb(68, 68, 68); border-radius: 4px; display: block; margin: 0px 0px 1.5em; font-size: 14px; line-height: 1.5em; word-break: break-all; overflow-wrap: break-word; white-space: pre; background-color: rgb(246, 246, 246); border: none; overflow-x: auto; font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-align: start; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;">public interface 接口名 {}</pre>

    • 类实现接口用 **implements** 表示

    <pre class="prettyprint hljs php" style="padding: 0.5em; font-family: Menlo, Monaco, Consolas, "Courier New", monospace; color: rgb(68, 68, 68); border-radius: 4px; display: block; margin: 0px 0px 1.5em; font-size: 14px; line-height: 1.5em; word-break: break-all; overflow-wrap: break-word; white-space: pre; background-color: rgb(246, 246, 246); border: none; overflow-x: auto; font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-align: start; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;">public class 类名 implements 接口名 {}</pre>

    • 接口不能实例化

    接口如何实例化呢？参照多态的方式，通过实现类对象实例化，这叫接口多态。 多态的形式：具体类多态，抽象类多态，接口多态。

    • 接口的子类

    要么重写接口中的所有抽象方法 要么子类也是抽象类

    1.3接口的成员特点

    • **成员特点 **

    • 成员变量

    只能是常量 默认修饰符： public static final

    • 构造方法

    没有，因为接口主要是扩展功能的，而没有具体存在

    • **成员方法 **

    只能是抽象方法 默认修饰符： **public abstract ** 关于接口中的方法，JDK8和JDK9中有一些新特性。有兴趣的大家可以去 官网 查一下相关的API。

    接下来我们通过一个案例将其简单的说明，具体代码演示如下：

    • **接口 **

    <pre class="prettyprint hljs java" style="padding: 0.5em; font-family: Menlo, Monaco, Consolas, "Courier New", monospace; color: rgb(68, 68, 68); border-radius: 4px; display: block; margin: 0px 0px 1.5em; font-size: 14px; line-height: 1.5em; word-break: break-all; overflow-wrap: break-word; white-space: pre; background-color: rgb(246, 246, 246); border: none; overflow-x: auto; font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-align: start; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;">public interface Inter {
    public int num = 10;
    public final int num2 = 20;
    // public static final int num3 = 30;
    int num3 = 30;

    // public Inter() {}

    // public void show() {}

    public abstract void method();
void show();

    }</pre>

    • **实现类 **

    <pre class="prettyprint hljs java" style="padding: 0.5em; font-family: Menlo, Monaco, Consolas, "Courier New", monospace; color: rgb(68, 68, 68); border-radius: 4px; display: block; margin: 0px 0px 1.5em; font-size: 14px; line-height: 1.5em; word-break: break-all; overflow-wrap: break-word; white-space: pre; background-color: rgb(246, 246, 246); border: none; overflow-x: auto; font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-align: start; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;">public class InterImpl extends Object implements Inter {
    public InterImpl() {
    super();
    }

    @Override
public void method() {
    System.out.println("method");
}

@Override
public void show() {
    System.out.println("show");
}

    }</pre>

    • **测试类 **

    <pre class="prettyprint hljs cs" style="padding: 0.5em; font-family: Menlo, Monaco, Consolas, "Courier New", monospace; color: rgb(68, 68, 68); border-radius: 4px; display: block; margin: 0px 0px 1.5em; font-size: 14px; line-height: 1.5em; word-break: break-all; overflow-wrap: break-word; white-space: pre; background-color: rgb(246, 246, 246); border: none; overflow-x: auto; font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-align: start; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;">public class InterfaceDemo {
    public static void main(String[] args) {
    Inter i = new InterImpl();
    // i.num = 20;
    System.out.println(i.num);
    // i.num2 = 40;
    System.out.println(i.num2);
    System.out.println(Inter.num);
    }
    }</pre>

    该案例的具体执行结果如下：

    [图片上传失败...(image-81583c-1649227245224)]

    1.4接口的案例

    • 案例需求

    对猫和狗进行训练，他们就可以跳高了，这里加入跳高功能。 请采用抽象类和接口来实现猫狗案例，并在测试类中进行测试。

    • 代码实现：

    • 动物类

    <pre class="prettyprint hljs java" style="padding: 0.5em; font-family: Menlo, Monaco, Consolas, "Courier New", monospace; color: rgb(68, 68, 68); border-radius: 4px; display: block; margin: 0px 0px 1.5em; font-size: 14px; line-height: 1.5em; word-break: break-all; overflow-wrap: break-word; white-space: pre; background-color: rgb(246, 246, 246); border: none; overflow-x: auto; font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-align: start; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;">public abstract class Animal {
    private String name;
    private int age;

    public Animal() {
}

public Animal(String name, int age) {
    this.name = name;
    this.age = age;
}

public String getName() {
    return name;
}

public void setName(String name) {
    this.name = name;
}

public int getAge() {
    return age;
}

public void setAge(int age) {
    this.age = age;
}

public abstract void eat();

    }</pre>

    • **跳高接口 **

    <pre class="prettyprint hljs java" style="padding: 0.5em; font-family: Menlo, Monaco, Consolas, "Courier New", monospace; color: rgb(68, 68, 68); border-radius: 4px; display: block; margin: 0px 0px 1.5em; font-size: 14px; line-height: 1.5em; word-break: break-all; overflow-wrap: break-word; white-space: pre; background-color: rgb(246, 246, 246); border: none; overflow-x: auto; font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-align: start; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;">public interface Jumpping {
    public abstract void jump();
    }</pre>

    • **猫类 **

    <pre class="prettyprint hljs java" style="padding: 0.5em; font-family: Menlo, Monaco, Consolas, "Courier New", monospace; color: rgb(68, 68, 68); border-radius: 4px; display: block; margin: 0px 0px 1.5em; font-size: 14px; line-height: 1.5em; word-break: break-all; overflow-wrap: break-word; white-space: pre; background-color: rgb(246, 246, 246); border: none; overflow-x: auto; font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-align: start; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;">public class Cat extends Animal implements Jumpping {

    public Cat() {
}

public Cat(String name, int age) {
    super(name, age);
}

@Override
public void eat() {
    System.out.println("猫吃鱼");
}

@Override
public void jump() {
    System.out.println("猫可以跳高了");
}

    }</pre>

    • **测试类 **

    <pre class="prettyprint hljs swift" style="padding: 0.5em; font-family: Menlo, Monaco, Consolas, "Courier New", monospace; color: rgb(68, 68, 68); border-radius: 4px; display: block; margin: 0px 0px 1.5em; font-size: 14px; line-height: 1.5em; word-break: break-all; overflow-wrap: break-word; white-space: pre; background-color: rgb(246, 246, 246); border: none; overflow-x: auto; font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-align: start; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;">public class AnimalDemo {
    public static void main(String[] args) {
    //创建对象，调用方法
    Jumpping j = new Cat();
    j.jump();
    System.out.println("--------");

        Animal a = new Cat();
    a.setName("加菲");
    a.setAge(5);
    System.out.println(a.getName()+","+a.getAge());
    a.eat();

    // a.jump();

        a = new Cat("加菲",5);
    System.out.println(a.getName()+","+a.getAge());
    a.eat();
    System.out.println("--------");

    Cat c = new Cat();
    c.setName("加菲");
    c.setAge(5);
    System.out.println(c.getName()+","+c.getAge());
    c.eat();
    c.jump();
}

    }</pre>

    该案例具体的执行结果如下：

    [图片上传失败...(image-136623-1649227245224)]

    1.5类和接口的关系

    • 类与类的关系

    继承关系，只能单继承，但是可以多层继承

    • 类与接口的关系

    实现关系，可以单实现，也可以多实现，还可以在继承一个类的同时实现多个接口

    • **接口与接口的关系 **

    继承关系，可以单继承，也可以多继承

    1.6抽象类和接口的区别

    • **成员区别 **

    • 抽象类

    变量,常量；有构造方法；有抽象方法,也有非抽象方法

    • 接口

    常量；抽象方法

    • 关系区别

    • **类与类 **

    继承，单继承

    • **类与接口 **

    实现，可以单实现，也可以多实现

    • 接口与接口

    继承，单继承，多继承

    • **设计理念区别 **

    • 抽象类

    对类抽象，包括属性、行为

    • **接口 **

    对行为抽象，主要是行为

    2.综合案例

    2.1案例需求

    我们现在有乒乓球运动员和篮球运动员，乒乓球教练和篮球教练。 为了出国交流，跟乒乓球相关的人员都需要学习英语。 请用所学知识分析，这个案例中有哪些具体类，哪些抽象类，哪些接口，并用代码实现。

    这些类之间的关系如下：

    [图片上传失败...(image-f78d82-1649227245223)]

    2.2代码实现

    根据以上的需求以及类之间的关系，我们给出如下的代码实现，首先我们给出的是抽象出来的人类：

    • ** 抽象人类 **

    <pre class="prettyprint hljs java" style="padding: 0.5em; font-family: Menlo, Monaco, Consolas, "Courier New", monospace; color: rgb(68, 68, 68); border-radius: 4px; display: block; margin: 0px 0px 1.5em; font-size: 14px; line-height: 1.5em; word-break: break-all; overflow-wrap: break-word; white-space: pre; background-color: rgb(246, 246, 246); border: none; overflow-x: auto; font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-align: start; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;">public abstract class Person {
    private String name;
    private int age;

    public Person() {
}

public Person(String name, int age) {
    this.name = name;
    this.age = age;
}

public String getName() {
    return name;
}

public void setName(String name) {
    this.name = name;
}

public int getAge() {
    return age;
}

public void setAge(int age) {
    this.age = age;
}

public abstract void eat();

    }</pre>

    • **抽象运动员类 **

    <pre class="prettyprint hljs scala" style="padding: 0.5em; font-family: Menlo, Monaco, Consolas, "Courier New", monospace; color: rgb(68, 68, 68); border-radius: 4px; display: block; margin: 0px 0px 1.5em; font-size: 14px; line-height: 1.5em; word-break: break-all; overflow-wrap: break-word; white-space: pre; background-color: rgb(246, 246, 246); border: none; overflow-x: auto; font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-align: start; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;">public abstract class Player extends Person {
    public Player() {
    }

    public Player(String name, int age) {
    super(name, age);
}

public abstract void study();

    }</pre>

    • **抽象教练类 **

    <pre class="prettyprint hljs scala" style="padding: 0.5em; font-family: Menlo, Monaco, Consolas, "Courier New", monospace; color: rgb(68, 68, 68); border-radius: 4px; display: block; margin: 0px 0px 1.5em; font-size: 14px; line-height: 1.5em; word-break: break-all; overflow-wrap: break-word; white-space: pre; background-color: rgb(246, 246, 246); border: none; overflow-x: auto; font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-align: start; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;">public abstract class Coach extends Person {
    public Coach() {
    }

    public Coach(String name, int age) {
    super(name, age);
}

public abstract void teach();

    }</pre>

    • **学英语接口 **

    <pre class="prettyprint hljs java" style="padding: 0.5em; font-family: Menlo, Monaco, Consolas, "Courier New", monospace; color: rgb(68, 68, 68); border-radius: 4px; display: block; margin: 0px 0px 1.5em; font-size: 14px; line-height: 1.5em; word-break: break-all; overflow-wrap: break-word; white-space: pre; background-color: rgb(246, 246, 246); border: none; overflow-x: auto; font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-align: start; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;">public interface SpeakEnglish {
    public abstract void speak();
    }</pre>

    • **蓝球教练 **

    <pre class="prettyprint hljs java" style="padding: 0.5em; font-family: Menlo, Monaco, Consolas, "Courier New", monospace; color: rgb(68, 68, 68); border-radius: 4px; display: block; margin: 0px 0px 1.5em; font-size: 14px; line-height: 1.5em; word-break: break-all; overflow-wrap: break-word; white-space: pre; background-color: rgb(246, 246, 246); border: none; overflow-x: auto; font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-align: start; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;">public class BasketballCoach extends Coach {
    public BasketballCoach() {
    }

    public BasketballCoach(String name, int age) {
    super(name, age);
}

@Override
public void teach() {
    System.out.println("篮球教练教如何运球和投篮");
}

@Override
public void eat() {
    System.out.println("篮球教练吃羊肉，喝羊奶");
}

    }</pre>

    • 乒乓球教练

    <pre class="prettyprint hljs java" style="padding: 0.5em; font-family: Menlo, Monaco, Consolas, "Courier New", monospace; color: rgb(68, 68, 68); border-radius: 4px; display: block; margin: 0px 0px 1.5em; font-size: 14px; line-height: 1.5em; word-break: break-all; overflow-wrap: break-word; white-space: pre; background-color: rgb(246, 246, 246); border: none; overflow-x: auto; font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-align: start; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;">public class PingPangCoach extends Coach implements SpeakEnglish {

    public PingPangCoach() {
}

public PingPangCoach(String name, int age) {
    super(name, age);
}

@Override
public void teach() {
    System.out.println("乒乓球教练教如何发球和接球");
}

@Override
public void eat() {
    System.out.println("乒乓球教练吃小白菜，喝大米粥");
}

@Override
public void speak() {
    System.out.println("乒乓球教练说英语");
}

    }</pre>

    • **乒乓球运动员 **

    <pre class="prettyprint hljs java" style="padding: 0.5em; font-family: Menlo, Monaco, Consolas, "Courier New", monospace; color: rgb(68, 68, 68); border-radius: 4px; display: block; margin: 0px 0px 1.5em; font-size: 14px; line-height: 1.5em; word-break: break-all; overflow-wrap: break-word; white-space: pre; background-color: rgb(246, 246, 246); border: none; overflow-x: auto; font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-align: start; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;">public class PingPangPlayer extends Player implements SpeakEnglish {

    public PingPangPlayer() {
}

public PingPangPlayer(String name, int age) {
    super(name, age);
}

@Override
public void study() {
    System.out.println("乒乓球运动员学习如何发球和接球");
}

@Override
public void eat() {
    System.out.println("乒乓球运动员吃大白菜，喝小米粥");
}

@Override
public void speak() {
    System.out.println("乒乓球运动员说英语");
}

    }</pre>

    • 篮球运动员

    <pre class="prettyprint hljs java" style="padding: 0.5em; font-family: Menlo, Monaco, Consolas, "Courier New", monospace; color: rgb(68, 68, 68); border-radius: 4px; display: block; margin: 0px 0px 1.5em; font-size: 14px; line-height: 1.5em; word-break: break-all; overflow-wrap: break-word; white-space: pre; background-color: rgb(246, 246, 246); border: none; overflow-x: auto; font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-align: start; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;">public class BasketballPlayer extends Player {

    public BasketballPlayer() {
}

public BasketballPlayer(String name, int age) {
    super(name, age);
}

@Override
public void study() {
    System.out.println("篮球运动员学习如何运球和投篮");
}

@Override
public void eat() {
    System.out.println("篮球运动员吃牛肉，喝牛奶");
}

    }</pre>

    • 测试类

    <pre class="prettyprint hljs cs" style="padding: 0.5em; font-family: Menlo, Monaco, Consolas, "Courier New", monospace; color: rgb(68, 68, 68); border-radius: 4px; display: block; margin: 0px 0px 1.5em; font-size: 14px; line-height: 1.5em; word-break: break-all; overflow-wrap: break-word; white-space: pre; background-color: rgb(246, 246, 246); border: none; overflow-x: auto; font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-align: start; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;">/*
    测试类
    */
    public class PersonDemo {
    public static void main(String[] args) {
    //创建对象
    PingPangPlayer ppp = new PingPangPlayer();
    ppp.setName("王浩");
    ppp.setAge(30);
    System.out.println(ppp.getName()+","+ppp.getAge());
    ppp.eat();
    ppp.study();
    ppp.speak();
    System.out.println("--------");

        BasketballPlayer bp = new BasketballPlayer();
    bp.setName("姚明");
    bp.setAge(35);
    System.out.println(bp.getName()+","+bp.getAge());
    bp.eat();
    bp.study();
}

    }</pre>

    该案例执行的结果如下：

    [图片上传失败...(image-bd00c-1649227245223)]Java三大特性之接口

    总结

    本文主要给大家介绍了Java中三大特性中的接口，至此，我们java中的三大特性都给大家介绍完毕，这是我们Java开发中最基础也是最常用的。希望大家认真掌握，打好基础才能走的更远。

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