src/java.base/share/classes/java/util/Collection.java

rev 48060 : 8060192: Add default method <A> A[] Collection.toArray(IntFunction<A[]> generator)
Reviewed-by: XXX

*** 23,32 ****
--- 23,33 ----
   * questions.
   */
  
  package java.util;
  
+ import java.util.function.IntFunction;
  import java.util.function.Predicate;
  import java.util.stream.Stream;
  import java.util.stream.StreamSupport;
  
  /**
*** 327,336 ****
--- 328,374 ----
       *         runtime component type} of the specified array
       * @throws NullPointerException if the specified array is null
       */
      <T> T[] toArray(T[] a);
  
+     /**
+      * Returns an array containing all of the elements in this collection,
+      * using the provided {@code generator} function to allocate the returned array.
+      *
+      * <p>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.
+      *
+      * <p>Like the {@link #toArray()} method, this method acts as bridge between
+      * array-based and collection-based APIs.  Further, this method allows
+      * precise control over the runtime type of the output array.
+      *
+      * <p>Suppose {@code x} is a collection known to contain only strings.
+      * The following code can be used to dump the collection into a newly
+      * allocated array of {@code String}:
+      *
+      * <pre>
+      *     String[] y = x.toArray(String[]::new);</pre>
+      *
+      * @implSpec
+      * The default implementation calls the generator function with zero
+      * and then passes the resulting array to {@link #toArray(T[])}.
+      *
+      * @param <T> the component type of the array to contain the collection
+      * @param generator a function which produces a new array of the desired
+      *                  type and the provided length
+      * @return an array containing all of the elements 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 array returned by the generator function
+      * @throws NullPointerException if the generator function is null
+      * @since 10
+      */
+     default <T> T[] toArray(IntFunction<T[]> generator) {
+         return toArray(generator.apply(0));
+     }
+ 
      // Modification Operations
  
      /**
       * Ensures that this collection contains the specified element (optional
       * operation).  Returns {@code true} if this collection changed as a