4847239: (spec) File.createTempFile() should make it clear that it doesn't create the temporary directory

Reviewed-by: naoto, lancea

src/java.base/share/classes/java/io/File.java

@@ -2110,6 +2110,13 @@ public class File
      * is invoked, but programmatic changes to this property are not guaranteed
      * to have any effect upon the temporary directory used by this method.
      *
+     * <p> If the {@code directory} argument is not {@code null} and its
+     * abstract pathname is valid and denotes an existing, writable directory,
+     * then the file will be created in that directory. Otherwise the file will
+     * not be created and an {@code IOException} will be thrown.  Under no
+     * circumstances will a directory be created at the location specified by
+     * the {@code directory} argument.
+     *
      * @param  prefix     The prefix string to be used in generating the file's
      *                    name; must be at least three characters long
      *
@@ -2127,7 +2134,8 @@ public class File
      *          If the {@code prefix} argument contains fewer than three
      *          characters
      *
-     * @throws  IOException  If a file could not be created
+     * @throws  IOException
+     *          If a file could not be created
      *
      * @throws  SecurityException
      *          If a security manager exists and its {@link
@@ -2149,6 +2157,7 @@ public class File
 
         File tmpdir = (directory != null) ? directory
                                           : TempDirectory.location();
+
         @SuppressWarnings("removal")
         SecurityManager sm = System.getSecurityManager();
         File f;