@Deprecated新外观可能是什么？

JDK增强建议（JEP）277（“ 增强的弃用 ”）建议“重新定义弃用注释，并提供工具来增强功能生命周期的尾端。” 当前@ java.lang.Deprecated的一些限制使我困扰了一段时间。我特别希望能够使用@Deprecated提供文本，而不是被迫在相应的Javadoc @deprecated注释中放置说明性文本。在这篇文章中，我看了一个自定义批注，它给人一种JEP 277建议包含在新的和改进的@Deprecated批注中的额外元数据类型的感觉。

dustin.examples.annotations.Deprecated的代码清单包含dustin.examples.annotations.Deprecated的定义，该实现主要反映JEP 277提案中描述的内容。

不推荐使用dustin.examples.annotations。

package dustin.examples.annotations;import java.lang.annotation.Documented;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;import static java.lang.annotation.ElementType.*;
import static java.lang.annotation.ElementType.TYPE;/*** Conceptual improvement on standard @java.lang.Deprecated annotation* based on preliminary discussion related to JEP 277 and on* desire to include context details with deprecation annotation* rather than relying on presence of Javadoc's @deprecated.** Javadoc comments in this annotation definition are largely* based on descriptions in JEP 277 (http://openjdk.java.net/jeps/277).*/
@Documented
@Retention(RetentionPolicy.RUNTIME)
@Target({CONSTRUCTOR,FIELD,LOCAL_VARIABLE,METHOD,PACKAGE,PARAMETER,TYPE})
public @interface Deprecated
{/*** JEP 277-defined reasons and associated explanations.*/public enum Reason{/*** This API has been deprecated without any reason having been given.* This is the default value; everything that's deprecated today* implicitly has a deprecation reason of UNSPECIFIED.*/UNSPECIFIED,/*** This API is earmarked for removal in a future JDK release. Note,* the use of the word "condemned" here is used in the sense of a* structure that is intended to be torn down. The term is not mean* to imply any moral censure.*/CONDEMNED,/*** Use of this API can lead to data loss, deadlock, security* vulnerability, incorrect results, or loss of JVM integrity.*/DANGEROUS,/*** This API is no longer necessary, and usages should be removed.* No replacement API exists. Note that OBSOLETE APIs might or* might not be marked CONDEMNED.*/OBSOLETE,/*** This API has been replaced by a newer API, and usages should be* migrated away from this API to the newer API. Note that SUPERSEDED* APIs might or might not be marked CONDEMNED.*/SUPERSEDED,/*** Calling this has no effect or will unconditionally throw an exception.*/UNIMPLEMENTED,/*** This API is not a stable part of the specification, and it may* change incompatibly or disappear at any time.*/EXPERIMENTAL;}/*** Provides any combination of one or more of the enum constants,* although not all combinations make sense. It is syntactically possible,* though perverse, to provide an empty array. Such a case should be* treated as if UNSPECIFIED were present.** @return One or more Reasons for deprecation; default value is the enum*    constant UNSPECIFIED and absence of values should be treated as such.*/Reason[] value();/*** Provides Strings representing any APIs that replace this API.* This should not specify any replacements if reason is OBSOLETE.** @return Strings returned by this method should be links to replacement*    APIs for the API being deprecated. Each string should be in the same*    format as the @link Javadoc tag.*/String[] replacement();/*** Provides the release in which the API was deprecated.** @return Release number at which this API became deprecated*    in a free-form syntax String with the release numbering*    following the same scheme as the @since Javadoc tag.*/String since();/*** Provides the anticipated complete removal of this deprecated API* if any known date or version is anticipated for the API's removal.* This value is most likely to be set for reasons of CONDEMNED,* OBSOLETE, and SUPERSEDED. This value is NOT described in JEP 277.** @return Date or version in which it is anticipated that this*    API will be removed altogether.*/String anticipatedRemoval() default "Not Planned";
}

下一个代码清单提供了将上述注释应用于不推荐使用的类的示例。

DeprecatedClass.java：使用改进的@Deprecated的示例

package dustin.examples.annotations.demo;import java.text.DateFormat;
import java.text.SimpleDateFormat;import static dustin.examples.annotations.Deprecated.Reason.*;/*** Demonstrates how new and improved @Deprecated might be used.*/
@dustin.examples.annotations.Deprecated(value={SUPERSEDED, CONDEMNED},since="1.5", anticipatedRemoval="1.9",replacement="dustin.examples.annotations.demo.OtherClass")
public class DeprecatedClass
{final DateFormat dateFormat = new SimpleDateFormat("yyyy-MM-dd'T'HH:mm:ss.SSSZ");@dustin.examples.annotations.Deprecated(value={DANGEROUS}, since="1.0",replacement="java.text.SimpleDateFormat#SimpleDateFormat")public DateFormat getDateFormatter(){return dateFormat;}
}

最后一个示例演示了改进的@Deprecated注释的@Deprecated 。该“ anticipatedRemoval中的”元素@Deprecated注释不JEP 277中提到，我给它一个默认值，其中，过时的构造可能没有预期的拆除日期，而是已被弃用，以吓退只有它的新用途的情况。

上面的代码清单演示了定义一个新的和经过改进的@Deprecated批注（例如JEP 277中阐明的注释）。但是，JEP 277提出的内容远不止存在一种改进的批注。该提案还讨论了“运行时更改”，以提供“关于在选择加入的基础上使用已弃用API的警告”，“依赖工具增强”，以类似于jdeps工具甚至可能基于jdeps工具的方式分析注释依赖，以及“ Javadoc增强功能。”

尽管Java的自定义批注支持使实现@Deprecated的版本很容易实现，该版本反映了JEP 277中的许多思想，但是经过改进的新版@java.lang.Deprecated将具有许多自定义Java批注不具备的优点，例如内置-JDK中的-in支持并由JDK类使用。由JDK提供的@Deprecated也将继续享受IDE和工具带来的好处，例如删除不赞成使用的代码结构的名称。