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找不到令人兴奋的符号?[重复]

compiler-errors methods class java

0

AISAN · 技术社区 · 4 年前

创造了一个 AnimalPet 班

class AnimelPet {
    int ageInMonths;
    String breed;
    
    AnimelPet(int ageInMonths, String breed) {
        this.ageInMonths = ageInMonths;
        this.breed = breed;
    }
}

创造了一个 Worker 班

class Worker {
    int ageInYears;
    String name;
    int yearOfWork;
    
    Worker(int ageInYears, int yearOfWork, String name) {
        this.ageInYears = ageInYears;
        this.name = name;
        this.yearOfWork = yearOfWork;
    }
}

这个 Main 班

public class MainFile { 
    public static void main(String[] args) {
        AnimelPet kitten = new AnimelPet(12, "European shorthair");
        Worker Anna = new Worker(21, 5, "Anna Java");
        infoPet(Anna);
    }
    
    private static <T> void isYoung(T petObj) {
        if(petObj instanceof AnimelPet) {
            if(petObj.ageInMonths < 4) {
                System.out.println("The cat is pretty young!");
            } 
            else if (petObj.ageInMonths > 4) {
                System.out.println("The cat is old!");
            }
        } 
        else if(petObj instanceof Worker) {
            if (petObj.ageInYears < 18) {
                System.out.println("The worker is underage!");
            }
            else if (petObj.ageInYears > 18) {
                System.out.println("The worker is overage!");
            }
        }
    }
}

得到 error: cannot find symbol 对于以下变量:

ageInYears
ageInMonths

1 回复 | 直到 4 年前

1

0

dani-vta 4 年前

您无法检查泛型类型的变量是否是特定类的实例,然后在不先强制转换它的情况下引用其字段。

在你的 isYoung 方法只需检查 petObj 是动物宠物的一个例子。对于编译器来说,在类型擦除之后,petObj仍然是一个对象实例;因此,您需要按如下方式强制转换变量以使用其成员:

public class MainFile { 
    public static void main(String[] args) {
        AnimelPet kitten = new AnimelPet(12, "European shorthair");
        Worker Anna = new Worker(21, 5, "Anna Java");
        infoPet(Anna);
    }
    
    private static <T> void isYoung(T petObj) {
        if(petObj instanceof AnimelPet) {
            AnimelPet pet = (AnimelPet) petObj;
            if(pet.ageInMonths < 4) {
                System.out.println("The cat is pretty young!");
            } 
            else if (pet.ageInMonths > 4) {
                System.out.println("The cat is old!");
            }
        } 
        else if(petObj instanceof Worker) {
            Worker work = (Worker) petObj;
            if (work.ageInYears < 18) {
                System.out.println("The worker is underage!");
            }
            else if (work.ageInYears > 18) {
                System.out.println("The worker is overage!");
            }
        }
    }
}

旁注:我想你想把你的班级叫做AnimalPet而不是AnimalPet。