为什么我在Java中得到NaN或null？ 公共类主{ 公共静态void main（字符串[]args）{ GroceryStore houstonStore=新杂货店（）； GroceryStore orlandoStore=新杂货店（）； GroceryStore seattleStore=新杂货店（）； double houstonStore收入=（houstonStore.AppleSold*houstonStore.applesPrice）+（houstonStore.OrangeSold*houstonStore.orangesPrice）； double OrlandostoreEvenue=（orlandoStore.AppleSold*orlandoStore.applesPrice）+（orlandoStore.OrangeSold*orlandoStore.orangesPrice）； 双座商店收入=（seattleStore.AppleSold*seattleStore.applesPrice）+（seattleStore.OrangeSold*seattleStore.orangesPrice）； houstonStore.applesSold=534； houstonStore.applesPrice=0.99； houstonStore.orangesSold=429； houstonStore.orangesPrice=0.87； System.out.println（“休斯顿商店收入为：“+houstonStoreRevenue”）； seattleStore.applesSold=765； seattleStore.applesPrice=0.86； seattleStore.orangesold=842； seattleStore.orangesPrice=0.91； System.out.println（“西雅图商店收入为：“+seattleStoreRevenue”）； orlandoStore.applesSold=402； orlandoStore.applesPrice=0.79； orlandoStore.orangesSold=398； orlandoStore.orangesPrice=0.77； System.out.println（“奥兰多商店的收入是：“+Orlandostreevenue”）； } }

我不太明白为什么我会得到下面的答案

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The Houston store revenue is: 0.0
The Seattle store revenue is: 0.0
The Orlando store revenue is: 0.0

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您正在引用尚未声明的属性。试试这个

public class Main {

    public static void main(String[] args) {
        GroceryStore houstonStore = new GroceryStore();
        GroceryStore orlandoStore = new GroceryStore();
        GroceryStore seattleStore = new GroceryStore();

        houstonStore.applesSold = 534;
        houstonStore.applesPrice = 0.99;
        houstonStore.orangesSold = 429;
        houstonStore.orangesPrice = 0.87;
        double houstonStoreRevenue = ( houstonStore.applesSold * houstonStore.applesPrice) + (houstonStore.orangesSold * houstonStore.orangesPrice);
        System.out.println("The Houston store revenue is: " + houstonStoreRevenue);

        seattleStore.applesSold = 765;
        seattleStore.applesPrice = 0.86;
        seattleStore.orangesSold = 842;
        seattleStore.orangesPrice = 0.91;
        double seattleStoreRevenue = (seattleStore.applesSold * seattleStore.applesPrice) + (seattleStore.orangesSold * seattleStore.orangesPrice);
        System.out.println("The Seattle store revenue is: " + seattleStoreRevenue);

        orlandoStore.applesSold = 402;
        orlandoStore.applesPrice = 0.79;
        orlandoStore.orangesSold = 398;
        orlandoStore.orangesPrice = 0.77;
        double orlandoStoreRevenue = (orlandoStore.applesSold * orlandoStore.applesPrice) + (orlandoStore.orangesSold * orlandoStore.orangesPrice );
        System.out.println("The Orlando store revenue is: " + orlandoStoreRevenue);
    }
}

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默认情况下，

GroceryStore

对象具有哪些值？因为您在设置这些值之前正在执行计算。默认值可能为零。（另一方面，您的对象还应该公开setter和getter，而不是允许使用代码直接访问值。这还允许您在对象本身上编写一个方法来执行计算，因此您不必重复该逻辑，只需查询对象即可。）请包括所有相关代码，以便其他人能够正确回答您的问题。在本例中，

GroceryStore

类丢失。我很困惑，为什么标题上写着“NaN或null”，但您的代码不生成这两个，而是生成

0

（零）。Nan或null在哪里？

public class Main {

    public static void main(String[] args) {
        GroceryStore houstonStore = new GroceryStore();
        GroceryStore orlandoStore = new GroceryStore();
        GroceryStore seattleStore = new GroceryStore();

        houstonStore.applesSold = 534;
        houstonStore.applesPrice = 0.99;
        houstonStore.orangesSold = 429;
        houstonStore.orangesPrice = 0.87;
        double houstonStoreRevenue = ( houstonStore.applesSold * houstonStore.applesPrice) + (houstonStore.orangesSold * houstonStore.orangesPrice);
        System.out.println("The Houston store revenue is: " + houstonStoreRevenue);

        seattleStore.applesSold = 765;
        seattleStore.applesPrice = 0.86;
        seattleStore.orangesSold = 842;
        seattleStore.orangesPrice = 0.91;
        double seattleStoreRevenue = (seattleStore.applesSold * seattleStore.applesPrice) + (seattleStore.orangesSold * seattleStore.orangesPrice);
        System.out.println("The Seattle store revenue is: " + seattleStoreRevenue);

        orlandoStore.applesSold = 402;
        orlandoStore.applesPrice = 0.79;
        orlandoStore.orangesSold = 398;
        orlandoStore.orangesPrice = 0.77;
        double orlandoStoreRevenue = (orlandoStore.applesSold * orlandoStore.applesPrice) + (orlandoStore.orangesSold * orlandoStore.orangesPrice );
        System.out.println("The Orlando store revenue is: " + orlandoStoreRevenue);
    }
}