Java反射——识别方法返回类型

Question

我有一个用例来确定方法的返回类型是否为List类型。 为了检查返回类型，我使用了Class#isAssignable方法并遇到了这种行为。

public class ObjectReturnType {
    public static void main(String[] args) throws NoSuchMethodException {
        Method method1 = ObjectReturnType.class.getDeclaredMethod("objectReturnType");
        Class<? extends Object> returnType1 = method1.getReturnType();
        if (returnType1.isAssignableFrom(List.class)) {
            System.out.println("Yes it is.");
        }

        Method declaredMethod2 = ObjectReturnType.class.getDeclaredMethod("listReturnType");
        Class<? extends Object> returnType2 = declaredMethod2.getReturnType();
        if (returnType2.isAssignableFrom(List.class)) {
            System.out.println("Yes it is.");
        }

    }

    public Object objectReturnType() {
        return null;
    }

    public List<String> listReturnType() {
        return List.of("");
    }
}

两种方法都通过if条件，我期望只有listReturnType方法通过if条件，不知道为什么objectReturnType方法会进入if条件。 有人可以帮助我理解这种行为吗？

Answer 1

您可以使用这样的类名进行检查

public class ObjectReturnType {

    public static void main(String[] args) throws NoSuchMethodException {
        Method method1 = ObjectReturnType.class.getDeclaredMethod("objectReturnType");
        Class<?> returnType1 = method1.getReturnType();
        if (List.class.getName().equals(returnType1.getName())) {
            System.out.println("Yes it is.");
        } else {
            System.out.println("Yes it not List.");
        }

        Method declaredMethod2 = ObjectReturnType.class.getDeclaredMethod("listReturnType");
        Class<?> returnType2 = declaredMethod2.getReturnType();
        if (List.class.getName().equals(returnType2.getName())) {
            System.out.println("Yes it is.");
        } else {
            System.out.println("Yes it not List.");
        }
    }

    public Object objectReturnType() {
        return null;
    }

    public List<String> listReturnType() {
        return List.of("");
    }

}

输出将是

No it not List.
Yes it is.