How can I do Java annotation like @name(“Luke”) with no attribute inside parenthesis?

问题

How I can do custom Java annotation with no attribute name inside parentheses?

I don't want this: @annotation_name(att=valor). I just want like in Servlets, i.e:

@WebServlet("/main")

回答1:

Define the annotation with an attribute named value, then the attribute name can be omitted:

@interface CustomAnnotation
{
    String value();
}

This can be used like so:

@CustomAnnotation("/main")
// ...

回答2:

You specify an attribute named value:

public @interface MyAnnotation {

    String value();

}

This doesn't have to be the only attribute if they have default values:

public @interface MyAnnotation {

    String value();
    int myInteger() default 0;

}

But if you want to explicitly assign a value to the attribute other than value, you then must explicitly assign value. That is to say:

@MyAnnotation("foo")
@MyAnnotation(value = "foo", myInteger = 1)

works

but

@MyAnnotatino("foo", myInteger = 1)

does not

回答3:

Quoting Annotations official documentation:

If there is just one element named value, then the name may be omitted, as in:

@SuppressWarnings("unchecked")
void myMethod() { }

This is how this annotation is defined:

public @interface SuppressWarnings {
  String[] value();
}

As you can see the documentation isn't entirely right, other attributes are also allowed ("just one element"), see WebServlet - but the one named value is treated differently.

来源：https://stackoverflow.com/questions/11786354/how-can-i-do-java-annotation-like-nameluke-with-no-attribute-inside-parenth

标签

java

attributes

annotations

default

parentheses