Question

如何将instanceof缩小到特定的孩子，而不必与父类结束。

例如，如果我应该有一个父类StackoverflowUsers，那么我有TenKUsers的直接子类，HundredKusers等等。现在我的问题是如何使用{{1}如果instanceof是Object的直接子类之一的实例，而不是最终选择StackoverflowUsers是object的实例。那可能吗？

Answer 1

只需使用instanceof TenKUsers（等）成语。

它会告诉您正在查看的对象是否是该基类的子对象。

由于您暗示TenKUsers是StackoverflowUsers的孩子，当然，instanceof StackoverflowUsers 对该对象来说是<{1}}。

Answer 2

您可以通过选中.getClass()排除超类本身，但是＆＃34;孙子＆＃34;也将匹配...

你可以使用反射，但一般情况下应该避免反思（有点＆＃34;作弊＆＃34;）。

public class T {

    static class StackoverflowUsers {}

    static class TenKUsers extends StackoverflowUsers {}
    static class HundredKusers extends StackoverflowUsers {}

    static class EtcEtc extends TenKUsers {}

    public static void main(String[] args) {

        System.out.println("Instance of String: "+checkInstance(new String()));
        System.out.println("Instance of StackoverflowUsers (superclass): "+checkInstance(new StackoverflowUsers()));
        System.out.println("Instance of TenKUsers (direct subclass): "+checkInstance(new TenKUsers()));
        System.out.println("Instance of HundredKusers (direct subclass): "+checkInstance(new HundredKusers()));
        System.out.println("Instance of EtcEtc (indirect subclass): "+checkInstance(new EtcEtc()));

        System.out.println();
        System.out.println("using reflection:");
        System.out.println("Instance of String: "+checkInstanceUsingReflection(new String()));
        System.out.println("Instance of StackoverflowUsers (superclass): "+checkInstanceUsingReflection(new StackoverflowUsers()));
        System.out.println("Instance of TenKUsers (direct subclass): "+checkInstanceUsingReflection(new TenKUsers()));
        System.out.println("Instance of HundredKusers (direct subclass): "+checkInstanceUsingReflection(new HundredKusers()));
        System.out.println("Instance of EtcEtc (indirect subclass): "+checkInstanceUsingReflection(new EtcEtc()));

    }

    private static boolean checkInstance(Object o) {
        return (o instanceof StackoverflowUsers) && (o.getClass() != StackoverflowUsers.class);
    }

    private static boolean checkInstanceUsingReflection(Object o) {
        Class<?> superclass = o.getClass().getSuperclass();
        return superclass == StackoverflowUsers.class;
    }
}

返回：

Instance of String: false
Instance of StackoverflowUsers (superclass): false
Instance of TenKUsers (direct subclass): true
Instance of HundredKusers (direct subclass): true
Instance of EtcEtc (indirect subclass): true

using reflection:
Instance of String: false
Instance of StackoverflowUsers (superclass): false
Instance of TenKUsers (direct subclass): true
Instance of HundredKusers (direct subclass): true
Instance of EtcEtc (indirect subclass): false

也许你应该重新考虑你的课程。似乎TenKUsers也可以是存储在StackoverflowUsers中的布尔标志。甚至更好：给你的StackoverflowUsers EnumSet<Archievments>并让Archievments包含＆＃34; TenKUser＆＃34;和＆＃34; HundredKusers＆＃34;。

Answer 3

除了Mena的答案之外，如果你想使用instanceof来检查，你可以使你的超类Stackoverflowusers抽象，以确保不存在任何实例，然后检查：

object instanceof Stackoverflowusers

将instanceof缩小到特定的子类

3 个答案: