java.lang.Readable
------------------

    /**
     * Reads all characters from this source and appends them to a destination
     * in the order in which they are read. On return, the source of characters
     * will be at its end.
     * <p>
     * This method may block indefinitely while reading from the source or
     * writing to the destination. If the source or destination is
     * {@link AutoCloseable closeable}, then the behavior when either is
     * <i>asynchronously closed</i>, or the thread is interrupted during the
     * transfer, is highly implementation-dependent and hence unspecified.
     * <p>
     * If an I/O error occurs during the operation, then not all characters
     * might have been transferred and the source or destination could be
     * left in an inconsistent state. The caller of this method should therefore
     * ensure in such a case that measures are taken to release any resources
     * held by the source and destination.
     *
     * @implSpec
     * The default implementation invokes the read method to read all characters
     * from this source and invokes the {@link Appendable#append(CharSequence, int, int)} 
     * method to write all characters to the appendable.
     * The total amount will be added up by after the write method has been 
     * completed.
     *
     * The default implementation behaves as if:
     * <pre>{@code
     *     long transferred = 0;
     *     CharBuffer buffer = CharBuffer.allocate(8192);
     *     int read;
     *     while ((read = this.read(buffer)) >= 0) {
     *         buffer.rewind();
     *         out.append(buffer, 0, read);
     *         transferred += read;
     *     }
     *     return transferred;
     * }</pre>
     *
     * @implNote
     * The default implementation should usually be overridden in cases where
     * the implementer is already a {@link CharSequence} or its data is already
     * available in the internal representation in order not having the extra
     * overhead creating a buffer in order to transfer its data to the 
     * destination.
     *
     * @param  out the appendable, non-null
     * @return the number of characters transferred
     * @throws IOException if an I/O error occurs when reading or writing
     * @throws NullPointerException if {@code out} is {@code null}
     *
     * @since 10
     */
    default long transferTo(Appendable out) throws IOException {
    ....
    }




java.nio.CharBuffer
-------------------

    /**
     * {@inheritDoc}
     *
     * @implSpec
     * The implementation is using two strategies of transferring data form the
     * actual source to the given destination. If the given {@link Appendable}
     * is a {@link CharBuffer} the transfer uses the {@code put(CharBuffer)}
     * method to transfer it's data if possible. For the other cases source
     * is passed into the {@link Appendable#append(CharSequence, int, int)}
     * method along with the current position and data length.
     *
     * @param  out the appendable, non-null
     * @return the number of characters transferred
     * @throws IOException if an I/O error occurs when reading or writing
     * @throws NullPointerException if {@code out} is {@code null}
     * @throws BufferOverflowException if there is insufficient space in this 
     *         buffer for the remaining chars in the source buffer
     * @throws IllegalArgumentException if out is this buffer
     * @throws ReadOnlyBufferException if out is a read-only buffer
     *
     * @since 10
     */
    @Override
    public long transferTo(Appendable out) throws IOException {
        int start = position();
        int length = remaining();
        if (out instanceof CharBuffer) {
            ((CharBuffer)out).put(this);
        } else {
            out.append(this, start, length);
        }
        return length;
    }