java - 在省略号前输入注解

Question

我在 JLS section 8.4 中看到过省略号前可以有注释:

class X {
    void method(String @Annotation ... x) {}
}

我的问题很简单:这是什么意思？

特别是，有什么区别:

class X {
    void method(@Annotation String ... x) {}
}

Answer 1

From the JLS on Where Annotations May Appear

It is possible for an annotation to appear at a syntactic location in a program where it could plausibly apply to a declaration, or a type, or both.

和

Whether an annotation applies to a declaration or to the type of the declared entity - and thus, whether the annotation is a declaration annotation or a type annotation - depends on the applicability of the annotation's type: [...]

因此，

中的注解

void method(String @Annotation ... x) {}

是一个TYPE_USE注解。

和注解在

void method(@Annotation String ... x) {}

既是TYPE_USE又是PARAMETER注释。

---

你可以验证这一点。

@Target(value = ElementType.TYPE_USE)
@interface Annot {}
public static void method(String @Annot... arg) {}
public static void method2(@Annot String... arg) {}

和

@Target(value = ElementType.PARAMETER)
@interface Annot {}
public static void method(String @Annot... arg) {} // DOES NOT COMPILE
public static void method2(@Annot String... arg) {}