How to use @value tag in javadoc?

Question

I am using a class with private constructor instead of an enum (this is a requirement). And now I am trying to add javadoc tags to document each public static final entity.

1) What is prefered place to put javadoc tags: like ob1 or ob2?

2) Both options generate error in IDEA @value tag must reference field with a constant intializer.

/**
 * {@value #ob1} object1 description
 */

public class MyClass {
    public static final Object ob1 = new Object();

    /**
     * {@value #ob2} object2 description
     */ 
    public static final Object ob2 = new Object();

    private MyClass() {}   
}

Solution 1

I don't think Kayaman's answer is sufficient as the question is how to use the @value tag in javadocs.

I think the problem lies in the fact that the value of the field being referenced is not a literal value.

In eclipse, when you have

/**
 * {@value #ob2} object2 description
 */ 
public static final Object ob2 = new Object();

the generated Javadocs are {@value #ob2} object2 description. However, when you have

/**
 * {@value #ob2} object2 description
 */ 
public static final String ob2 = "hello";

the generated Javadocs are "hello" object2 description (the expected output).

So, in summary, you are using the @value tag correctly in the javadocs but the value will only be rendered correctly if the field has been initialised with a literal value.

Solution 2

2) Both options generate error in IDEA @value tag must reference field with a constant intializer.

It does not make much sense to add non-constant expressions to the Javadoc.

At first, one might think that the most sensible behavior would be to add a toString to the Javadoc. But then, what happens if you had a mutable object like:

class MutableInteger {
    public int i;
    public String toString() { return Integer.toString(i); }
}

and a Javadoc like:

/**
 * {@value #obj}
 */
class Class {
    public static final MutableInteger obj = new MutableInteger(0);
}

Then one could simply do later on:

Class.obj.i = 1;

so adding 0 to the Javadoc wouldn't mean much.

It only works for strings because they are immutable and the JLS explicitly says so: there is no way for you to tell the compiler that on a custom class.

Comments

[Javaru]

To add to @JamesB answer, the value the @value parameter references has to be a constant (i.e. static and final) and be of a type that has a constant initializer. In general, this means Strings and primitives.

[juckele]

I fixed a similar error in my project by changing the @value to an @link.

[earcam]

Worth noting that you can only use @value within the same class (i.e. FQN prefixes before the # won't work)

[DavidS]

@earcam The Netbeans Javadoc tab resolves the \@value tag even with prefixes before the #. Possibly other IDEs do as well. Maybe the actual Javadoc tool (html generation) doesn't resolve them though -- I didn't test this.

[Flimtix]

Does this only work for constant values?