在Java超类型参考使用时isAnnotation present（）返回false [英] isAnnotationPresent() return false when used with super type reference in Java

问题描述

我试图让从超类型的引用变量使用反射，使该方法接受所有子类型的标注的详细信息。但 isAnnotation present（）返回假。同样与其他注释相关的方法。如果确切类型使用，如预期的输出。

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.

我知道，标注的信息将可以在即使我米通过超类型参照对象。

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
    }
}

如何获得注释信息？

How to get the annotation info?

推荐答案

您正在呼叫的getClass（）的在的一个类＆LT;＆GT; ，这将给类＆LT;班级＆GT; 。现在类本身的不的注释，这就是为什么你得到错误的。我想你想要的：

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));

这篇关于在Java超类型参考使用时isAnnotation present（）返回false的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！