What does @Deprecated mean on method parameters and local variables?
deprecated, java
Solution
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)
Problem
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 ```