Java中的思维导致运行时升级失败

运行此代码时，为什么会出现运行时错误？ 数组被定义为保存水果，但是在我用apple初始化它之后，我怎么能不给它水果呢

class Fruit{}
class Apple extends Fruit{}
class Jonathan extends Apple{}
class Orange extends Fruit{}

public class CovariantArrays {
    public static void main(String[] args) {
        Fruit[] fruit = new Apple[10];
        fruit[0] = new Apple();
        fruit[1] = new Jonathan();
        try {
            fruit[0] = new Fruit();
        } catch(Exception e) { System.out.println(e); }
        try {
            fruit[0] = new Orange();
        } catch(Exception e) { System.out.println(e); }
    }
}

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尝试将其放入数组类型：

fruit[0] = (Fruit) new Apple();

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原因是您试图将

水果

和

橙色

放入

苹果

中。 你只能把东西放进苹果[]里面，如果它真的是苹果的话

class Fruit{}
class Apple extends Fruit{}
class Jonathan extends Apple{}
class Orange extends Fruit{}
class BigApple extends Apple{}
class BigGreenApple extends BigApple{}

public class CovariantArrays {
    public static void main(String[] args) {
        Fruit[] fruit = new Apple[10];
        fruit[0] = new Apple();
        fruit[1] = new Jonathan(); // no error here since Jonathan is an Apple
        fruit[2] = new BigApple(); // still Apple
        fruit[3] = new BigGreenApple(); // no worries - still Apple
        fruit[4] = new Orange(); // Oops - Orange is a Fruit but its not Apple so error here
    }
}

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该阵列是一个

Apple[]

。为什么你会期望它能够容纳一些不是苹果的东西呢？