java @Deprecated 对方法参数和局部变量是什么意思？
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What does @Deprecated mean on method parameters and local variables?
提问by adarshr
DISCLAIMER: I know the meaning and purpose of @Deprecated.
免责声明：我知道@Deprecated.
The definition of the @Deprecatedannotation looks like this in the source code of Java:
@DeprecatedJava 源代码中注解的定义如下所示：
@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, METHODand PACKAGE.
我理解为目标值的目的CONSTRUCTOR，FIELD，TYPE，METHOD和PACKAGE。
However, what does it mean to mark a method parameter or a local variable as @Deprecated?
但是，将方法参数或局部变量标记为 是什么意思@Deprecated？
Strangely the below example compiles without any warnings.
奇怪的是，下面的示例编译时没有任何警告。
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?
这是他们将来可能打算实施的吗？
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.
FWIW，我在 Ubuntu 12.04 64 位上使用 JDK 1.7.0_11。无论我是从 Eclipse 还是命令行运行程序，结果都是一样的。
The compiler does spit out warnings for normalusage of @Deprecated, such as using one of the deprecated constructors of the java.util.Dateclass. Just to prove that I don't have a faulty terminal or set up, here is the output:
编译器确实会针对 的正常使用发出警告@Deprecated，例如使用java.util.Date该类的已弃用构造函数之一。只是为了证明我没有错误的终端或设置，这里是输出：
$ 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
采纳答案by Matt Ball
What does it mean to mark a method parameter or a local variable as
@Deprecated?
将方法参数或局部变量标记为 是什么意思
@Deprecated？
It has the same meaning as when applied to any other element:
A program element annotated
@Deprecatedis 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.
注释的程序元素
@Deprecated是程序员不鼓励使用的元素，通常是因为它很危险，或者因为存在更好的替代方案。当在非弃用代码中使用或覆盖已弃用的程序元素时，编译器会发出警告。
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.
为什么编译器不忽略 Java 7 中不推荐使用的参数和字段的警告？
因为这正是 JLS（第 9.6.3.6 节）所规定的。
A Java compiler must produce a deprecation warning when a type, method, field, or constructor whose declaration is annotated with the annotation
@Deprecatedis 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"); orThe use and declaration are both within the same outermost class.
Use of the
@Deprecatedannotation on a local variable declaration or on a parameter declaration has no effect.
当
@Deprecated使用（即覆盖、调用或按名称引用）声明带有注解的类型、方法、字段或构造函数时，Java 编译器必须产生弃用警告，除非：
使用在一个实体中，该实体本身用@Deprecated 注释；或者
使用在一个被注释的实体中以抑制带有注释的警告
@SuppressWarnings("deprecation")；或者使用和声明都在同一个最外层类中。
@Deprecated在局部变量声明或参数声明上使用注释无效。
(emphasis added)
（强调）
回答by Stephen C
The JLS expressly states that the @Deprecation annotation is ignored on local variables. See Matt Ball's answer.
JLS 明确指出@Deprecation 注释在局部变量上被忽略。参见马特鲍尔的回答。
Is this something they might intend to implement in the future?
这是他们将来可能打算实施的吗？
I very much doubt it.
我非常怀疑。
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 materialchange 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.
这意味着什么......除了作为对实现者（可能还有样式检查器 / PMD / FindBugs / 等）的非正式提醒的当前含义之外，需要删除局部变量。
对于当前使用上述注释的人来说，任何重大更改都可能破坏源代码兼容性。Java 维护人员非常努力地避免破坏旧代码。
回答by Sandeep T
If you compile such a code (ex:mvn clean compile) you get following warning message
如果您编译这样的代码（例如：mvn clean compile），您会收到以下警告消息
@Deprecated annotation has no effect on this variable declaration
@Deprecated annotation has no effect on this variable declaration
meaning its useless :)
意思是没用:)
