前言：本篇博客，适合刚刚学完java基础语法的但是，对于面向对象，理解不够深刻的读者，本文通过经典的宠物商店，来让读者深刻的理解，面向对象，IS-A，HAS-A法则。本文不仅仅是简单的用java来模拟一个宠物商店，而是通过分析宠物商店的业务，来让大家理解，最简单的业务逻辑，即商店，商品，用户，这三者的逻辑，这个代码同样可以适用于，图书管理系统，书店管理系统，宿舍管理系统等等的入门理解。

好了本文开始了。首先我们先把题目给出来。

题目

业务逻辑分析

首先是分析，宠物店，动物，小猫小狗，客户之间的关系，其中最为明显的就是，小猫小狗与动物之间的关系，很显然小猫小狗继承动物的属性，他们之间属于IS-A，什么是IS-A法则，就是这种继承关系，所以，我们可以构建Animal类，思考所有动物的公共属性，比如我这里写的这个Animal类中的姓名，价格，性别，颜色，年龄这些成员，因为是举例子，所以很多地方并不会写的很全，然后再分析行为，我这里设计的他们的共有行为便是，Shout()，大叫属性。

当Animal这个基类成功之后，那么后续就是，设计猫类，狗类了，对于这两个类的话，为了方便理解，我们设置他们的新的成员是，对于猫来说为CatPara，对于狗来说的话是DogPara，然后他们会重写父类的Shout()方法，这里就体现了面向对象里面的多态，具体代码如下。

动物类的编写

代码如下：

/*
* 讲解面向对象的三个基本特性
* IS-A法则
* HAS-A法则
* */// 动物类
class Animal{private String name;  // 姓名private Double price; // 价格private Boolean sex; // 性别private String color; // 颜色 private Integer age; // 年龄public Animal() {}public void Shout(){ // 大叫System.out.println("大声的叫");}public String getName() {return name;}public void setName(String name) {this.name = name;}public Double getPrice() {return price;}public void setPrice(Double price) {this.price = price;}public Boolean getSex() {return sex;}public void setSex(Boolean sex) {this.sex = sex;}public String getColor() {return color;}public void setColor(String color) {this.color = color;}public Integer getAge() {return age;}public void setAge(Integer age) {this.age = age;}@Overridepublic String toString() { // 重写toString()方法 方便遍历类return "Animal{" +"name='" + name + '\'' +", price=" + price +", sex=" + sex +", color='" + color + '\'' +", age=" + age +'}';}
}// 狗类
class Dog extends Animal{ // Dog is a animal // 继承父类属性 这里体现了继承private Integer DogPara; // 狗参数public Integer getDogPara() {return DogPara;}public void setDogPara(Integer dogPara) {DogPara = dogPara;}public void WagTail(){ // 对于小狗添加了一个新的摇尾巴的方法System.out.println("摇尾巴");}public Dog() {}@Overridepublic void Shout(){   // 重写父类的方法 这里体现了多态System.out.println("汪汪汪");}@Overridepublic String toString() {return "Dog{" +"DogPara=" + DogPara + " " + super.toString() +'}';}
}// 猫类
class Cat extends Animal{private Integer CatPara; // 猫参数public Integer getCatPara() {return CatPara;}public void setCatPara(Integer catPara) {CatPara = catPara;}public void LickHair(){   // 对于小猫 添加一个舔毛的方法System.out.println("舔毛");}public Cat() {}@Overridepublic void Shout(){ // 重写父类属性System.out.println("喵喵喵");}@Overridepublic String toString() {  // 重写toString()方法 方便遍历类return "Cat{" +			// super()调用父类的toString()方法 可以简写很多。"CatPara=" + CatPara + " " + super.toString() +'}';}
}

宠物店类的编写

对于宠物店类，和宠物的关系，这里属于的是HAS-A法则，HAS-A法则什么意思了，比如，汽车与轮胎之间的关系，轮胎属于汽车，在这个例题中的情况就是，宠物属于宠物店，这就是HAS-A法则。

/*
* Has-A法则
*
* */
// 宠物店类
class PetShop{// 这里体现了HAS-A法则 宠物店包含小猫，小狗这些宠物private ArrayList dogs;  // 宠物店的小狗的集合private ArrayList cats;  // 宠物店中小猫的集合public PetShop() {  // 构造方法中加上代码 随机的生成初始数据Random random = new Random();dogs = new ArrayList<>();cats = new ArrayList<>();for (int i = 0; i < 100; i++) {Dog dog = new Dog();Cat cat = new Cat();dog.setName("dog" + i);cat.setName("cat" + i);dog.setPrice(random.nextDouble() * 400 + 100); // [0,1) * 400 = [0, 400) + 100 = [100, 500)cat.setPrice(random.nextDouble() * 400 + 100); // [0,1) * 400 = [0, 400) + 100 = [100, 500)dog.setSex(random.nextBoolean());cat.setSex(random.nextBoolean());dog.setDogPara(random.nextInt(1000));cat.setCatPara(random.nextInt(1000));dog.setColor(random.nextInt(1000) + ":" + random.nextInt(1000) + ":" + random.nextInt(1000));cat.setColor(random.nextInt(1000) + ":" + random.nextInt(1000) + ":" + random.nextInt(1000));dog.setAge(random.nextInt(10));cat.setAge(random.nextInt(10));dogs.add(dog);cats.add(cat);}}public void Traversal(){  // 遍历现有数据for (int i = 0; i < dogs.size(); i++) {System.out.println(dogs.get(i));}System.out.println("----------------------------------");Iterator iterator2 = cats.iterator();while(iterator2.hasNext()){System.out.println(iterator2.next());}}public int getNumDog(){return dogs.size();}public int getNumCat(){return cats.size();}public ArrayList getDogs() {return dogs;}public void setDogs(ArrayList dogs) {this.dogs = dogs;}public ArrayList getCats() {return cats;}public void setCats(ArrayList cats) {this.cats = cats;}
}

客户类的编写

这时候我们就需要分析最后一种关系，客户与宠物店之间的关系，它们之间的关系，是两个单独的个体，至于怎么联合起来，通过客户类中的Buy(PetShop petShop)行为就可以理解了。

class Custom{private Boolean sex;private Integer age;private String name;private ArrayList dogs;private ArrayList cats;public Custom() {}public Custom(String name) {this.name = name;}public boolean Buy(PetShop petShop){ // 这是客户在宠物店中购买商品的情况 // 因为这是一个讲解面向对象的，所以这里作者就先不补全了，示意即可Scanner in = new Scanner(System.in);System.out.println("Y/N"); // 小狗就是Y 小猫就是NString flag = in.nextLine().toLowerCase();if (flag.equals("y")){}else {}return false;}public Boolean getSex() {return sex;}public void setSex(Boolean sex) {this.sex = sex;}public Integer getAge() {return age;}public void setAge(Integer age) {this.age = age;}public ArrayList getDogs() {return dogs;}public void setDogs(ArrayList dogs) {this.dogs = dogs;}public ArrayList getCats() {return cats;}public void setCats(ArrayList cats) {this.cats = cats;}
}

代码汇总

通过该文章的这个例题的简介，基本上就讲解完了，面向对象的基础和IS-A,HAS-A法则。

import java.util.ArrayList;
import java.util.Iterator;
import java.util.Random;
import java.util.Scanner;/*
* 讲解面向对象的三个基本特性
* IS-A法则
* HAS-A法则
* */
class Animal{private String name;  // 姓名private Double price; // 价格private Boolean sex; // 性别private String color; // 颜色 private Integer age; // 年龄public Animal() {}public void Shout(){ // 大叫System.out.println("大声的叫");}public String getName() {return name;}public void setName(String name) {this.name = name;}public Double getPrice() {return price;}public void setPrice(Double price) {this.price = price;}public Boolean getSex() {return sex;}public void setSex(Boolean sex) {this.sex = sex;}public String getColor() {return color;}public void setColor(String color) {this.color = color;}public Integer getAge() {return age;}public void setAge(Integer age) {this.age = age;}@Overridepublic String toString() {return "Animal{" +"name='" + name + '\'' +", price=" + price +", sex=" + sex +", color='" + color + '\'' +", age=" + age +'}';}
}class Dog extends Animal{ // Dog is a animalprivate Integer DogPara;public Integer getDogPara() {return DogPara;}public void setDogPara(Integer dogPara) {DogPara = dogPara;}public void WagTail(){System.out.println("摇尾巴");}public Dog() {}@Overridepublic void Shout(){System.out.println("汪汪汪");}@Overridepublic String toString() {return "Dog{" +"DogPara=" + DogPara + " " + super.toString() +'}';}
}class Cat extends Animal{private Integer CatPara;public Integer getCatPara() {return CatPara;}public void setCatPara(Integer catPara) {CatPara = catPara;}public void LickHair(){System.out.println("舔毛");}public Cat() {}@Overridepublic void Shout(){System.out.println("喵喵喵");}@Overridepublic String toString() {return "Cat{" +"CatPara=" + CatPara + " " + super.toString() +'}';}
}/*
* Has-A法则
*
* */class PetShop{private ArrayList dogs;private ArrayList cats;public PetShop() {Random random = new Random();dogs = new ArrayList<>();cats = new ArrayList<>();for (int i = 0; i < 100; i++) {Dog dog = new Dog();Cat cat = new Cat();dog.setName("dog" + i);cat.setName("cat" + i);dog.setPrice(random.nextDouble() * 400 + 100); // [0,1) * 400 = [0, 400) + 100 = [100, 500)cat.setPrice(random.nextDouble() * 400 + 100); // [0,1) * 400 = [0, 400) + 100 = [100, 500)dog.setSex(random.nextBoolean());cat.setSex(random.nextBoolean());dog.setDogPara(random.nextInt(1000));cat.setCatPara(random.nextInt(1000));dog.setColor(random.nextInt(1000) + ":" + random.nextInt(1000) + ":" + random.nextInt(1000));cat.setColor(random.nextInt(1000) + ":" + random.nextInt(1000) + ":" + random.nextInt(1000));dog.setAge(random.nextInt(10));cat.setAge(random.nextInt(10));dogs.add(dog);cats.add(cat);}}public void Traversal(){for (int i = 0; i < dogs.size(); i++) {System.out.println(dogs.get(i));}System.out.println("----------------------------------");Iterator iterator2 = cats.iterator();while(iterator2.hasNext()){System.out.println(iterator2.next());}}public int getNumDog(){return dogs.size();}public int getNumCat(){return cats.size();}public ArrayList getDogs() {return dogs;}public void setDogs(ArrayList dogs) {this.dogs = dogs;}public ArrayList getCats() {return cats;}public void setCats(ArrayList cats) {this.cats = cats;}
}class Custom{private Boolean sex;private Integer age;private String name;private ArrayList dogs;private ArrayList cats;public Custom() {}public Custom(String name) {this.name = name;}public boolean Buy(PetShop petShop){Scanner in = new Scanner(System.in);System.out.println("Y/N"); // 小狗就是Y 小猫就是NString flag = in.nextLine().toLowerCase();if (flag.equals("y")){}else {}return false;}public Boolean getSex() {return sex;}public void setSex(Boolean sex) {this.sex = sex;}public Integer getAge() {return age;}public void setAge(Integer age) {this.age = age;}public ArrayList getDogs() {return dogs;}public void setDogs(ArrayList dogs) {this.dogs = dogs;}public ArrayList getCats() {return cats;}public void setCats(ArrayList cats) {this.cats = cats;}
}public class Main {public static void main(String[] args) {PetShop petShop = new PetShop(); // 创建一个宠物店
//        petShop.Traversal();Custom custom = new Custom("LiHua");}
}