import java.io.IOException;

/**
 * 能附加字符和值的对象.
 * 任何意图从{@linke java.util.Formatter}接收格式化流的类必须实现<tt>Appendable</tt>
 * 
 * <p>附加的字符必须是满足<a href="Character.html#unicode">Unicode</a>约束的字符.
 * 注意：附加的字符可能是16-bit字符值。
 * 
 * <p>因为实现类处理error的方式不同,所以不保证错误能够传递到调用者.
 * 
 */
/**
 * An object to which <tt>char</tt> sequences and values can be appended.  The
 * <tt>Appendable</tt> interface must be implemented by any class whose
 * instances are intended to receive formatted output from a {@link
 * java.util.Formatter}.
 *
 * <p> The characters to be appended should be valid Unicode characters as
 * described in <a href="Character.html#unicode">Unicode Character
 * Representation</a>.  Note that supplementary characters may be composed of
 * multiple 16-bit <tt>char</tt> values.
 *
 * <p> Appendables are not necessarily safe for multithreaded access.  Thread
 * safety is the responsibility of classes that extend and implement this
 * interface.
 *
 * <p> Since this interface may be implemented by existing classes
 * with different styles of error handling there is no guarantee that
 * errors will be propagated to the invoker.
 *
 * @since 1.5
 */
public interface Appendable {

    /**
     * 附加指定的字符序列到<tt>Appendable</tt>.
     * 
     * <p>由于实现CharSequence的类不同,整个序列可能不会被附加.比如<tt>csq</tt> 是 {@link java.nio.CharBuffer}.
     * 添加的子序列由buffer的position和limit决定.
     * 
     * @param csq
     *           待附加的序列,如果 <tt>csq</tt>是null,那么应该附加"null"这四个字符到Appendable内.
     * 
     * @return Appendable的引用.
     * 
     * @throws IOException
     *            出现I/O错误
     */
    /**
     * Appends the specified character sequence to this <tt>Appendable</tt>.
     *
     * <p> Depending on which class implements the character sequence
     * <tt>csq</tt>, the entire sequence may not be appended.  For
     * instance, if <tt>csq</tt> is a {@link java.nio.CharBuffer} then
     * the subsequence to append is defined by the buffer‘s position and limit.
     *
     * @param  csq
     *         The character sequence to append.  If <tt>csq</tt> is
     *         <tt>null</tt>, then the four characters <tt>"null"</tt> are
     *         appended to this Appendable.
     *
     * @return  A reference to this <tt>Appendable</tt>
     *
     * @throws  IOException
     *          If an I/O error occurs
     */
    Appendable append(CharSequence csq) throws IOException;

    /**
     * 附加一个指定的子序列到<tt>Appendable</tt>.
     * 
     * <p>当调用此方法的<tt>csq</tt>非null时，与下面这个调用等价.
     * <pre>
     *         out.append(csq.subSequence(start, end)) </pre>
     * 
     * 
     * @param csq
     *           待附加的序列,如果 <tt>csq</tt>是null,那么应该附加"null"这四个字符到Appendable内.
     * @param start
     *           第一个字符的索引
     * @param end
     *           最后一个字符索引的下一个索引
     * 
     */
    /**
     * Appends a subsequence of the specified character sequence to this
     * <tt>Appendable</tt>.
     *
     * <p> An invocation of this method of the form <tt>out.append(csq, start,
     * end)</tt> when <tt>csq</tt> is not <tt>null</tt>, behaves in
     * exactly the same way as the invocation
     *
     * <pre>
     *     out.append(csq.subSequence(start, end)) </pre>
     *     
     *
     * @param  csq
     *         The character sequence from which a subsequence will be
     *         appended.  If <tt>csq</tt> is <tt>null</tt>, then characters
     *         will be appended as if <tt>csq</tt> contained the four
     *         characters <tt>"null"</tt>.
     *
     * @param  start
     *         The index of the first character in the subsequence
     *
     * @param  end
     *         The index of the character following the last character in the
     *         subsequence
     *
     * @return  A reference to this <tt>Appendable</tt>
     *
     * @throws  IndexOutOfBoundsException
     *          If <tt>start</tt> or <tt>end</tt> are negative, <tt>start</tt>
     *          is greater than <tt>end</tt>, or <tt>end</tt> is greater than
     *          <tt>csq.length()</tt>
     *
     * @throws  IOException
     *          If an I/O error occurs
     */
    Appendable append(CharSequence csq, int start, int end) throws IOException;

    /**
     * 附加指定的字符到<tt>Appendable</tt>.
     */
    /**
     * Appends the specified character to this <tt>Appendable</tt>.
     *
     * @param  c
     *         The character to append
     *
     * @return  A reference to this <tt>Appendable</tt>
     *
     * @throws  IOException
     *          If an I/O error occurs
     */
    Appendable append(char c) throws IOException;
}