Summary
-------

Clarify specifications of Collection.toArray() and Collection.toArray(T[ ]).

Problem
-------

The Collection.toArray() method returns Object[] but it doesn't make clear that
the runtime type of the returned array must be Object[]. (Oddly, that is specified
in toArray(T[]) which is in the wrong place.) Also, there are a few locations in the
specs of toArray() and toArray(T[]) where they are imprecise about array types,
array component types, and runtime types.

Solution
--------

Adjust the wording of the specifications of these two methods. No code
or behavior changes are included in this changeset.

Specification
-------------

<pre><code>
diff -r 9bb771005928 src/java.base/share/classes/java/util/Collection.java
--- a/src/java.base/share/classes/java/util/Collection.java	Tue Nov 28 17:14:30 2017 -0800
+++ b/src/java.base/share/classes/java/util/Collection.java	Thu Nov 30 11:29:09 2017 -0800
@@ -266,21 +266,23 @@
 
     /**
      * Returns an array containing all of the elements in this collection.
      * If this collection makes any guarantees as to what order its elements
      * are returned by its iterator, this method must return the elements in
-     * the same order.
+     * the same order. The returned array's {@linkplain Class#getComponentType
+     * runtime component type} is {@code Object}.
      *
      * &lt;p>The returned array will be "safe" in that no references to it are
      * maintained by this collection.  (In other words, this method must
      * allocate a new array even if this collection is backed by an array).
      * The caller is thus free to modify the returned array.
      *
      * &lt;p>This method acts as bridge between array-based and collection-based
      * APIs.
      *
-     * @return an array containing all of the elements in this collection
+     * @return an array, whose {@linkplain Class#getComponentType runtime component
+     * type} is {@code Object}, containing all of the elements in this collection
      */
     Object[] toArray();
 
     /**
      * Returns an array containing all of the elements in this collection;
@@ -313,18 +315,18 @@
      *     String[] y = x.toArray(new String[0]);&lt;/pre>
      *
      * Note that {@code toArray(new Object[0])} is identical in function to
      * {@code toArray()}.
      *
-     * @param <T> the runtime type of the array to contain the collection
+     * @param <T> the component type of the array to contain the collection
      * @param a the array into which the elements of this collection are to be
      *        stored, if it is big enough; otherwise, a new array of the same
      *        runtime type is allocated for this purpose.
      * @return an array containing all of the elements in this collection
-     * @throws ArrayStoreException if the runtime type of the specified array
-     *         is not a supertype of the runtime type of every element in
-     *         this collection
+     * @throws ArrayStoreException if the runtime type of any element in this
+     *         collection is not assignable to the {@linkplain Class#getComponentType
+     *         runtime component type} of the specified array
      * @throws NullPointerException if the specified array is null
      */
     <T> T[] toArray(T[] a);
 
     // Modification Operations
</code></pre>