HADOOP-8059. Add javadoc to InterfaceAudience and InterfaceStability. Contributed by Brandon Li.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/trunk@1354684 13f79535-47bb-0310-9956-ffa450edef68
(cherry picked from commit 24c4216bf0d75006fb218d743183f96658bea65c)

Conflicts:
	hadoop-common-project/hadoop-common/CHANGES.txt

hadoop-common-project/hadoop-annotations/src/main/java/org/apache/hadoop/classification/InterfaceAudience.java

@@ -23,6 +23,24 @@ import java.lang.annotation.RetentionPolicy;
 
 /**
  * Annotation to inform users of a package, class or method's intended audience.
+ * Currently the audience can be {@link Public}, {@link LimitedPrivate} or
+ * {@link Private}. <br>
+ * All public classes must have InterfaceAudience annotation. <br>
+ * <ul>
+ * <li>Public classes that are not marked with this annotation must be
+ * considered by default as {@link Private}.</li> 
+ * 
+ * <li>External applications must only use classes that are marked
+ * {@link Public}. Avoid using non public classes as these classes
+ * could be removed or change in incompatible ways.</li>
+ * 
+ * <li>Hadoop projects must only use classes that are marked
+ * {@link LimitedPrivate} or {@link Public}</li>
+ * 
+ * <li> Methods may have a different annotation that it is more restrictive
+ * compared to the audience classification of the class. Example: A class 
+ * might be {@link Public}, but a method may be {@link LimitedPrivate}
+ * </li></ul>
  */
 @InterfaceAudience.Public
 @InterfaceStability.Evolving

hadoop-common-project/hadoop-annotations/src/main/java/org/apache/hadoop/classification/InterfaceStability.java

@@ -21,9 +21,20 @@ import java.lang.annotation.Documented;
 import java.lang.annotation.Retention;
 import java.lang.annotation.RetentionPolicy;
 
+import org.apache.hadoop.classification.InterfaceAudience.LimitedPrivate;
+import org.apache.hadoop.classification.InterfaceAudience.Private;
+import org.apache.hadoop.classification.InterfaceAudience.Public;
+
 /**
  * Annotation to inform users of how much to rely on a particular package,
- * class or method not changing over time.
+ * class or method not changing over time. Currently the stability can be
+ * {@link Stable}, {@link Evolving} or {@link Unstable}. <br>
+ * 
+ * <ul><li>All classes that are annotated with {@link Public} or
+ * {@link LimitedPrivate} must have InterfaceStability annotation. </li>
+ * <li>Classes that are {@link Private} are to be considered unstable unless
+ * a different InterfaceStability annotation states otherwise.</li>
+ * <li>Incompatible changes must not be made to classes marked as stable.</li>
  */
 @InterfaceAudience.Public
 @InterfaceStability.Evolving

hadoop-common-project/hadoop-common/CHANGES.txt

@@ -262,6 +262,9 @@ Release 2.7.0 - UNRELEASED
 
     HADOOP-11714. Add more trace log4j messages to SpanReceiverHost (cmccabe)
 
+    HADOOP-8059. Add javadoc to InterfaceAudience and InterfaceStability.
+    (Brandon Li via suresh)
+
   OPTIMIZATIONS
 
     HADOOP-11323. WritableComparator#compare keeps reference to byte array.