Add EnumMap.keyType() and EnumSet.elementType()

[Andrej Golovnin]

Hi all,

it would be nice if we would have access to the class of the enum type
used to create an EnumMap or an EnumSet.

This is usefull when you write a custom serialization library and
would like to serialize/deserialize an empty EnumMap or an empty
EnumSet. For the empty EnumSet there is a workaround to get the enum
class:

EnumSet<MyEnum> empty = EnumSet.noneOf(MyEnum.class);
EnumSet<MyEnum> tmp = EnumSet.complementOf(empty);
Class<?> elementType = tmp.iterator().next().getClass();

But this only works when the enum class has at least one enum. For
EnumMap there is no such workaround at all and we have to use the
Reflection API. And you know the warnings since Java 9 :-) :

WARNING: An illegal reflective access operation has occurred
WARNING: Illegal reflective access by c.r.r.k.EnumMapSerializer to
field java.util.EnumMap.keyType
WARNING: Please consider reporting this to the maintainers of
c.r.r.k.EnumMapSerializer
WARNING: Use --illegal-access=warn to enable warnings of further
illegal reflective access operations
WARNING: All illegal access operations will be denied in a future release

So to avoid this warning and to avoid that our application stops to
work with a future release of Java I would like to propose to add the
following two methods:

EnumMap:
    /**
     * Returns the {@code Class} object of the key type for this enum map.
     *
     * @return the {@code Class} object of the key type for this enum map.
     *
     * @since 10
     */
    public Class<K> keyType()


EnumSet:
    /**
     * Returns the {@code Class} object of all the elements of this set.
     *
     * @return the {@code Class} object of all the elements of this set.
     *
     * @since 10
     */
    public Class<E> elementType()

The suggested change is attached as diff.

Best reagrds,
Andrej Golovnin
-------------- next part --------------
diff --git a/src/java.base/share/classes/java/util/EnumMap.java b/src/java.base/share/classes/java/util/EnumMap.java
--- a/src/java.base/share/classes/java/util/EnumMap.java
+++ b/src/java.base/share/classes/java/util/EnumMap.java
@@ -179,6 +179,17 @@
         }
     }
 
+    /**
+     * Returns the {@code Class} object of the key type for this enum map.
+     *
+     * @return the {@code Class} object of the key type for this enum map.
+     *
+     * @since 10
+     */
+    public Class<K> keyType() {
+        return keyType;
+    }
+
     // Query Operations
 
     /**
diff --git a/src/java.base/share/classes/java/util/EnumSet.java b/src/java.base/share/classes/java/util/EnumSet.java
--- a/src/java.base/share/classes/java/util/EnumSet.java
+++ b/src/java.base/share/classes/java/util/EnumSet.java
@@ -365,6 +365,17 @@
     }
 
     /**
+     * Returns the {@code Class} object of all the elements of this set.
+     *
+     * @return the {@code Class} object of all the elements of this set.
+     *
+     * @since 10
+     */
+    public Class<E> elementType() {
+        return elementType;
+    }
+
+    /**
      * Adds the specified range to this enum set, which is empty prior
      * to the call.
      */