Appendable.java

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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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 * accompanied this code).
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package java.lang;

import java.io.IOException;

/**
 * An object to which {@code char} sequences and values can be appended.  The
 * {@code Appendable} 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 {@code char} 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
 */
// 添加字符的接口。代表该对象具有添加字符序列的能力
public interface Appendable {
    
    /**
     * Appends the specified character sequence to this {@code Appendable}.
     *
     * <p> Depending on which class implements the character sequence
     * {@code csq}, the entire sequence may not be appended.  For
     * instance, if {@code csq} 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 {@code csq} is
     *            {@code null}, then the four characters {@code "null"} are
     *            appended to this Appendable.
     *
     * @return A reference to this {@code Appendable}
     *
     * @throws IOException If an I/O error occurs
     */
    // 向该对象添加一个字符序列
    Appendable append(CharSequence csq) throws IOException;
    
    /**
     * Appends a subsequence of the specified character sequence to this
     * {@code Appendable}.
     *
     * <p> An invocation of this method of the form {@code out.append(csq, start, end)}
     * when {@code csq} is not {@code null}, 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 {@code csq} is {@code null}, then characters
     *              will be appended as if {@code csq} contained the four
     *              characters {@code "null"}.
     * @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 {@code Appendable}
     *
     * @throws IndexOutOfBoundsException If {@code start} or {@code end} are negative, {@code start}
     *                                   is greater than {@code end}, or {@code end} is greater than
     *                                   {@code csq.length()}
     * @throws IOException               If an I/O error occurs
     */
    // 向该对象添加一个字符序列，该字符序列是csq在[start, end)范围内的一个子序列
    Appendable append(CharSequence csq, int start, int end) throws IOException;
    
    /**
     * Appends the specified character to this {@code Appendable}.
     *
     * @param c The character to append
     *
     * @return A reference to this {@code Appendable}
     *
     * @throws IOException If an I/O error occurs
     */
    // 向该对象添加一个字符
    Appendable append(char c) throws IOException;
}