6733145: (bf) CharBuffer.subSequence can be updated to take advantage of covariant returns

Summary: Change return type to CharBuffer
Reviewed-by: alanb

src/share/classes/java/nio/ByteBufferAs-X-Buffer.java

@@ -186,7 +186,7 @@ class ByteBufferAs$Type$Buffer$RW$$BO$                  // package-private
 
     // --- Methods to support CharSequence ---
 
-    public CharSequence subSequence(int start, int end) {
+    public CharBuffer subSequence(int start, int end) {
         int pos = position();
         int lim = limit();
         assert (pos <= lim);

src/share/classes/java/nio/Direct-X-Buffer.java

@@ -402,7 +402,7 @@ class Direct$Type$Buffer$RW$$BO$
 
     // --- Methods to support CharSequence ---
 
-    public CharSequence subSequence(int start, int end) {
+    public CharBuffer subSequence(int start, int end) {
         int pos = position();
         int lim = limit();
         assert (pos <= lim);

src/share/classes/java/nio/Heap-X-Buffer.java

@@ -566,7 +566,7 @@ class Heap$Type$Buffer$RW$
 
     // --- Methods to support CharSequence ---
 
-    public CharSequence subSequence(int start, int end) {
+    public CharBuffer subSequence(int start, int end) {
         if ((start < 0)
             || (end > length())
             || (start > end))

src/share/classes/java/nio/StringCharBuffer.java

@@ -99,7 +99,7 @@ class StringCharBuffer                                  // package-private
         return str.toString().substring(start + offset, end + offset);
     }
 
-    public final CharSequence subSequence(int start, int end) {
+    public final CharBuffer subSequence(int start, int end) {
         try {
             int pos = position();
             return new StringCharBuffer(str, -1,

src/share/classes/java/nio/X-Buffer.java

@@ -1239,13 +1239,13 @@ public abstract class $Type$Buffer
      *         smaller than <tt>start</tt> and no larger than
      *         <tt>remaining()</tt>
      *
-     * @return  The new character sequence
+     * @return  The new character buffer
      *
      * @throws  IndexOutOfBoundsException
      *          If the preconditions on <tt>start</tt> and <tt>end</tt>
      *          do not hold
      */
-    public abstract CharSequence subSequence(int start, int end);
+    public abstract CharBuffer subSequence(int start, int end);
 
 
     // --- Methods to support Appendable ---