8202216: Add Buffer mismatch methods

Reviewed-by: plevart, psandoz

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

@@ -1353,6 +1353,38 @@ public abstract class $Type$Buffer
 #end[floatingPointType]
     }
 
+    /**
+     * Finds and returns the relative index of the first mismatch between this
+     * buffer and a given buffer.  The index is relative to the
+     * {@link #position() position} of each buffer and will be in the range of
+     * 0 (inclusive) up to the smaller of the {@link #remaining() remaining}
+     * elements in each buffer (exclusive).
+     *
+     * <p> If the two buffers share a common prefix then the returned index is
+     * the length of the common prefix and it follows that there is a mismatch
+     * between the two buffers at that index within the respective buffers.
+     * If one buffer is a proper prefix of the other then the returned index is
+     * the smaller of the remaining elements in each buffer, and it follows that
+     * the index is only valid for the buffer with the larger number of
+     * remaining elements.
+     * Otherwise, there is no mismatch.
+     *
+     * @param  that
+     *         The byte buffer to be tested for a mismatch with this buffer
+     *
+     * @return  The relative index of the first mismatch between this and the
+     *          given buffer, otherwise -1 if no mismatch.
+     *
+     * @since 11
+     */
+    public int mismatch($Type$Buffer that) {
+        int length = Math.min(this.remaining(), that.remaining());
+        int r = BufferMismatch.mismatch(this, this.position(),
+                                        that, that.position(),
+                                        length);
+        return (r == -1 && this.remaining() != that.remaining()) ? length : r;
+    }
+
     // -- Other char stuff --
 
 #if[char]