What does @Deprecated mean on method parameters and local variables?

Question

DISCLAIMER: I know the meaning and purpose of @Deprecated.

The definition of the @Deprecated annotation looks like this in the source code of Java:

@Documented
@Retention(RetentionPolicy.RUNTIME)
@Target(value={CONSTRUCTOR, FIELD, LOCAL_VARIABLE, METHOD, PACKAGE, PARAMETER, TYPE})
public @interface Deprecated {
}

I understand the purpose of having target values of CONSTRUCTOR, FIELD, TYPE, METHOD and PACKAGE.

However, what does it mean to mark a method parameter or a local variable as @Deprecated?

Strangely the below example compiles without any warnings.

interface Doable {
    void doIt(@Deprecated Object input);
}

class Action implements Doable {

    @Override
    public void doIt(@Deprecated Object input) {

        String string = String.valueOf(input); // no warning!

        @Deprecated
        String localVariable = "hello";

        System.out.println("Am I using a deprecated variable?" + localVariable); // no warning!
    }
}

Is this something they might intend to implement in the future?

---

FWIW, I use JDK 1.7.0_11 on Ubuntu 12.04 64bit. The result is the same whether I run the program from Eclipse or command line.

The compiler does spit out warnings for normal usage of @Deprecated, such as using one of the deprecated constructors of the java.util.Date class. Just to prove that I don't have a faulty terminal or set up, here is the output:

$ javac com/adarshr/Test.java -Xlint:deprecation
com/adarshr/Test.java:12: warning: [deprecation] Date(int,int,int) in Date has been deprecated
        new Date(2013, 1, 31);
        ^
1 warning
$ 
$ javac -version
javac 1.7.0_11

Answer 1

What does it mean to mark a method parameter or a local variable as @Deprecated?

It has the same meaning as when applied to any other element:

A program element annotated @Deprecated is one that programmers are discouraged from using, typically because it is dangerous, or because a better alternative exists. Compilers warn when a deprecated program element is used or overridden in non-deprecated code.

---

Why doesn't the compiler omit warnings for deprecated parameters and fields in Java 7?
Because that's exactly what the JLS (§ 9.6.3.6) dictates.

A Java compiler must produce a deprecation warning when a type, method, field, or constructor whose declaration is annotated with the annotation @Deprecated is used (i.e. overridden, invoked, or referenced by name), unless:

• The use is within an entity that is itself annotated with the annotation @Deprecated; or

• The use is within an entity that is annotated to suppress the warning with the annotation @SuppressWarnings("deprecation"); or

• The use and declaration are both within the same outermost class.

Use of the @Deprecated annotation on a local variable declaration or on a parameter declaration has no effect.

(emphasis added)

Answer 2

The JLS expressly states that the @Deprecation annotation is ignored on local variables. See Matt Ball's answer.

Is this something they might intend to implement in the future?

I very much doubt it.

• What could it mean ... apart from its current meaning as an informal reminder to the implementor (and maybe style checkers / PMD / FindBugs / etc) that the local variable needs to be removed.

• Any material change is likely to break source compatibility for people who currently use the annotation as above. The Java maintainers try very hard to avoid breaking old code.