Java - Why array constants aren't allowed as Annotation attribute value? [duplicate]

Question

public Class Constants {
    public static final String single = "aabbcc";
    public static final String[] ttt = {"aa", "bb", "cc"};
}

@Retention(RetentionPolicy.RUNTIME)
@Target({ElementType.PARAMETER, ElementType.FIELD})
public @interface Anno {
    String aaa() default "aaa"; //this is allowed.
    String bbb() default Constants.single; //this is allowed.
    String[] ccc() default {}; //this is also allowed.
    String[] ddd() default Constants.ttt; //while this is not!
}

as the example shown above, I don't get it why String array constants are not allowed as annotation attribute value?

I don't believe there's such a thing as an "array constant" in Java... the syntax you give is an "array initializer" with runtime semantics. — Jim Garrison
– Jim Garrison, Commented Jan 23, 2016 at 5:59

Erwin Bolwidt · Accepted Answer · 2016-01-23 06:26:01Z

3

Like Jim Garrison mentioned in a comment, there is no such thing as an "array constant" in Java.

It is easily demonstrated that an array is not a constant:

// Right now, Constants.ttt contains {"aa", "bb", "cc"}
Constants.ttt[1] = "foobar";
// Right now, Constants.ttt contains {"aa", "foobar", "cc"}

So it's not so much that String array constants are not allowed, as that there is no such thing as a String array constant in Java.

answered Jan 23, 2016 at 6:26

Erwin Bolwidt

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