2.20.成熟的类的对象要自己做事情

把操作成员变量的代码放在类里
初始化成员变量

简单访问和设置成员变量的值 （ Java Bean ）

专有的一些计算逻辑

用类定义成员变量，并把操作成员变量的代码都放在类里，就是封装：
• 可以集中管控，自己的成员变量别人不可以乱来，避免出现非法的状态，比如库存为负数
• 代码逻辑可以公用，避免代码重复，修改的时候只需改一处
• 封装的好，可以更好的抽象一类事物

public class LittleSuperMarket {
    public String superMarketName;
    public String address;
    public int parkingCount;
    public double incomingSum;
    public MerchandiseV2[] merchandises;
    public int[] merchandiseSold;

    /**
     * 初始化小超市
     *
     * @param superMarketName
     * @param address
     * @param parkingCount
     * @param merchandiseCount 商品种类数
     * @param count            每种商品缺省库存
     */
    public void init(String superMarketName, String address, int parkingCount,
                     int merchandiseCount, int count) {
        this.superMarketName = superMarketName;
        this.address = address;
        this.parkingCount = parkingCount;

        merchandises = new MerchandiseV2[merchandiseCount];
        for (int i = 0; i < merchandises.length; i++) {
            // 创建并给商品的属性赋值
            MerchandiseV2 m = new MerchandiseV2();
            m.name = "商品" + i;
            m.count = count;
            m.purchasePrice = Math.random() * 200;
            m.soldPrice = m.purchasePrice * (1 + Math.random());
            m.id = "ID" + i;
            // 用创建的商品，给商品数组的第i个引用赋值，all和小超市的商品数组引用指向的是同一个数组对象
            merchandises[i] = m;
        }
        merchandiseSold = new int[merchandises.length];
    }

    // 简单的访问成员变量

    public String getSuperMarketName() {
        return superMarketName;
    }

    public String getAddress() {
        return address;
    }

    public int getParkingCount() {
        return parkingCount;
    }

    public double getIncomingSum() {
        return incomingSum;
    }

    public void setSuperMarketName(String superMarketName) {
        this.superMarketName = superMarketName;
    }

    public void setAddress(String address) {
        this.address = address;
    }

    public void setParkingCount(int parkingCount) {
        this.parkingCount = parkingCount;
    }

    public void setIncomingSum(double incomingSum) {
        this.incomingSum = incomingSum;
    }

    public void setMerchandises(MerchandiseV2[] merchandises) {
        this.merchandises = merchandises;
    }

    public void setMerchandiseSold(int[] merchandiseSold) {
        this.merchandiseSold = merchandiseSold;
    }

    // 一些特殊的逻辑

    /**
     * 得到利润最高的商品
     *
     * @return
     */
    public MerchandiseV2 getBiggestProfitMerchandise() {
        MerchandiseV2 curr = null;
        for (int i = 0; i < merchandises.length; i++) {
            MerchandiseV2 m = merchandises[i];
            // 这个逻辑有问题吗？相同的利润怎么判断？
            if (curr == null || curr.calculateProfit() < m.calculateProfit()) {
                curr = m;
            }
        }
        return curr;
    }

    /**
     * 根据索引获取商品
     *
     * @param merchandiseIndex
     * @return
     */
    public MerchandiseV2 getMerchandiseOf(int merchandiseIndex) {
        if (merchandiseIndex < 0 || merchandiseIndex >= merchandises.length) {
            return null;
        }
        return merchandises[merchandiseIndex];
    }

    /**
     * 赚钱
     * @param toBeAdded
     */
    public void addIncomingSum(double toBeAdded) {
        this.incomingSum += toBeAdded;
    }

    /**
     * 花钱
     * @param toBeSpent
     * @return
     */
    public boolean spendMoney(double toBeSpent) {
        if (toBeSpent > incomingSum) {
            return false;
        }
        incomingSum -= toBeSpent;
        return true;
    }

}

public class MerchandiseV2 {

    public String name;
    public String id;
    public int count;
    public double soldPrice;
    public double purchasePrice;

    public void init(String name, String id, int count, double soldPrice, double purchasePrice) {
        this.name = name;
        this.id = id;
        this.count = count;
        this.soldPrice = soldPrice;
        this.purchasePrice = purchasePrice;
    }

    // >> TODO 定义方法
    public void describe() {
        System.out.println("商品名字叫做" + name + "，id是" + id + "。 商品售价是" + soldPrice
            + "。商品进价是" + purchasePrice + "。商品库存量是" + count +
            "。销售一个的毛利润是" + (soldPrice - purchasePrice));
    }

    // >> TODO 定义方法
    public double calculateProfit() {
        double profit = soldPrice - purchasePrice;
//        if(profit <= 0){
//            return 0;
//        }
        return profit;
    }

    public double buy(int count) {
        if (this.count < count) {
            return -1;
        }

        return this.count -= count;
    }
}

public class RunLittleSupperMarketAppMain {
    public static void main(String[] args) {
        // 创建一个小超市类
        LittleSuperMarket littleSuperMarket = new LittleSuperMarket();
        littleSuperMarket.init("有家小超市", "浦东新区世纪大道666号",
            100, 200, 200);
//        // 依次给超市的名字，地址，停车位赋值
//        littleSuperMarket.superMarketName = "有家小超市";
//        littleSuperMarket.address = "浦东新区世纪大道666号";
//        littleSuperMarket.parkingCount = 100;
//        // 给超市200种商品
//        littleSuperMarket.merchandises = new MerchandiseV2[200];
//        // 统计用的数组
//        littleSuperMarket.merchandiseSold = new int[littleSuperMarket.merchandises.length];
//
//        // 为了使用方便，创建一个商品数组引用，和littleSuperMarket.merchandises指向同一个数组对象
//        MerchandiseV2[] all = littleSuperMarket.merchandises;
//
//        // 遍历并给200种商品赋值
//        for (int i = 0; i < all.length; i++) {
//            // 创建并给商品的属性赋值
//            MerchandiseV2 m = new MerchandiseV2();
//            m.name = "商品" + i;
//            m.count = 200;
//            m.purchasePrice = Math.random() * 200;
//            m.soldPrice = m.purchasePrice * (1 + Math.random());
//            m.id = "ID" + i;
//            // 用创建的商品，给商品数组的第i个引用赋值，all和小超市的商品数组引用指向的是同一个数组对象
//            all[i] = m;
//        }

        System.out.println("下面请利润最高的商品自我介绍：");
        littleSuperMarket.getBiggestProfitMerchandise().describe();
    }
}

```java
public class MerchandiseV2DescAppMain {
    public static void main(String[] args) {
        MerchandiseV2 merchandise = new MerchandiseV2();

//        merchandise.name = "书桌";
//        merchandise.soldPrice = 999.9;
//        merchandise.purchasePrice = 500;
//        merchandise.count = 40;
//        merchandise.id = "DESK9527";

        // >> TODO 调用方法，完成对成员变量的操作
        merchandise.init("书桌", "DESK9527", 40, 999.9, 500);

        merchandise.describe();
    }
}