你如何保证类注解参数扩展在编译时的界面？ [英] How do you ensure a class annotation parameter extends an interface at compile time?

问题描述

我有一个注释我试图定义需要一个Class参数。我想确保所提供的类继承的特定接口。所以，我想出了...

I have an annotation I'm attempting to define that takes a Class parameter. I would like to ensure that the Class provided extends a specific interface. So I came up with...

public @interface Tag {
    Class<? extends ITagStyle> style() default NoStyle.class
}
public class NoStyle implements ITagStyle {
    ...
}

不过，我得到不兼容的类型的编译错误。

However I get a compile error of "incompatible types".

我猜想这是因为 NoStyle.class 将返回类而不是类＆LT; NoStyle＆GT; 。在JLS对Java SE 5和7（找不到6，我用6）它专门说：void.class将返回类。查阅JLS类文字： http://docs.oracle.com/javase/specs/jls/se5.0/html/ex$p$pssions.html#15.8.2

I'm assuming this is because NoStyle.class is returning Class instead of Class<NoStyle>. In the JLS for Java SE 5 & 7 (couldn't find 6, I'm using 6) it specifically says that "void.class" would return "Class". SEE JLS Class literals: http://docs.oracle.com/javase/specs/jls/se5.0/html/expressions.html#15.8.2

反正在编译的时候做到这一点？如果不是我猜workround在运行时检查款式的值，以确保它延伸ITagStyle：（

Is there anyway to do this at compile time? If not I'm guessing the workround is to check the value of style at runtime to ensure it extends ITagStyle :'(

解决方案： JDeveloper已经在他们的过程的编译器的错误。检查进程外或使用JDK7u3纠正编译错误。

RESOLUTION: JDeveloper has a bug in their "in process" compiler. Checking "out of process" or using JDK7u3 corrects the compile error.

推荐答案

这工作的，所以要么你失去了一些东西明显或你的错误是没有关系的，你向我们展示了什么：

This works, so either you are missing something obvious or your error is not related to what you are showing us:

public class Test {

    public interface ITagStyle {
    }

    public @interface Tag {
        Class<? extends ITagStyle> style() default NoStyle.class;
    }

    public class NoStyle implements ITagStyle {
    }

    public class SomeStyle implements ITagStyle {

    }

    @Tag(style = SomeStyle.class)
    public static void main(String[] args) {

    }
}

本已在JDK 1.6.0_26测试

This has been tested on JDK 1.6.0_26

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