isAnnotationPresent() 在 Java 中与超类型引用一起使用时返回 false [英] isAnnotationPresent() return false when used with super type reference in Java

问题描述

我正在尝试使用反射从超类型引用变量中获取注释详细信息，以使该方法接受所有子类型.但是 isAnnotationPresent() 返回 false.与其他注释相关方法相同.如果在确切类型上使用，则输出符合预期.

I m trying to get the annotation details from super type reference variable using reflection, to make the method accept all sub types. But isAnnotationPresent() returning false. Same with other annotation related methods. If used on the exact type, output is as expected.

即使我通过超类型引用，我也知道注释信息将在对象上可用.

I know that annotation info will be available on the Object even I m referring through super type.

@Retention(RetentionPolicy.RUNTIME)
@Target({ElementType.TYPE})
public @interface Table {
    String name();
}
@Table(name = "some_table")
public class SomeEntity {

    public static void main(String[] args) {
        System.out.println(SomeEntity.class.isAnnotationPresent(Table.class)); // true
        System.out.println(new SomeEntity().getClass().isAnnotationPresent(Table.class)); // true

        Class<?> o1 = SomeEntity.class;
        System.out.println(o1.getClass().isAnnotationPresent(Table.class)); // false

        Class<SomeEntity> o2 = SomeEntity.class;
        System.out.println(o2.getClass().isAnnotationPresent(Table.class)); // false

        Object o3 = SomeEntity.class;
        System.out.println(o3.getClass().isAnnotationPresent(Table.class)); // false
    }
}

如何获取注解信息?

推荐答案

您正在调用 getClass() on 一个 Class，这将给出 Class.现在 Class 本身没有注释，这就是为什么你会得到错误.我想你想要:

You're calling getClass() on a Class<?>, which will give Class<Class>. Now Class itself isn't annotated, which is why you're getting false. I think you want:

// Note no call to o1.getClass()
Class<?> o1 = SomeEntity.class;
System.out.println(o1.isAnnotationPresent(Table.class));

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