StringWriter.java

/*
 * Copyright (c) 1996, 2016, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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 */

package java.io;


/**
 * A character stream that collects its output in a string buffer, which can
 * then be used to construct a string.
 * <p>
 * Closing a {@code StringWriter} has no effect. The methods in this class
 * can be called after the stream has been closed without generating an
 * {@code IOException}.
 *
 * @author Mark Reinhold
 * @since 1.1
 */
// String输出流：向字符串中写入字符
public class StringWriter extends Writer {
    
    private StringBuffer buf;   // 线程安全的字符序列
    
    
    
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    /**
     * Create a new string writer using the default initial string-buffer
     * size.
     */
    public StringWriter() {
        buf = new StringBuffer();
        lock = buf;
    }
    
    /**
     * Create a new string writer using the specified initial string-buffer
     * size.
     *
     * @param initialSize The number of {@code char} values that will fit into this buffer
     *                    before it is automatically expanded
     *
     * @throws IllegalArgumentException If {@code initialSize} is negative
     */
    public StringWriter(int initialSize) {
        if(initialSize<0) {
            throw new IllegalArgumentException("Negative buffer size");
        }
        buf = new StringBuffer(initialSize);
        lock = buf;
    }
    
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    /**
     * Write a single character.
     */
    // 将指定的字符写入到输出流
    public void write(int c) {
        buf.append((char) c);
    }
    
    /**
     * Write a portion of an array of characters.
     *
     * @param cbuf Array of characters
     * @param off  Offset from which to start writing characters
     * @param len  Number of characters to write
     *
     * @throws IndexOutOfBoundsException If {@code off} is negative, or {@code len} is negative,
     *                                   or {@code off + len} is negative or greater than the length
     *                                   of the given array
     */
    // 将字符数组cbuf中off处起的len个字符写入到输出流
    public void write(char[] cbuf, int off, int len) {
        if((off<0) || (off>cbuf.length) || (len<0) || ((off + len)>cbuf.length) || ((off + len)<0)) {
            throw new IndexOutOfBoundsException();
        } else if(len == 0) {
            return;
        }
        
        buf.append(cbuf, off, len);
    }
    
    
    /**
     * Write a string.
     */
    // 将字符串中的字符写入到输出流
    public void write(String str) {
        buf.append(str);
    }
    
    /**
     * Write a portion of a string.
     *
     * @param str String to be written
     * @param off Offset from which to start writing characters
     * @param len Number of characters to write
     *
     * @throws IndexOutOfBoundsException If {@code off} is negative, or {@code len} is negative,
     *                                   or {@code off + len} is negative or greater than the length
     *                                   of the given string
     */
    // 将字符串str中off处起的len个字符写入到输出流
    public void write(String str, int off, int len) {
        buf.append(str, off, off + len);
    }
    
    
    /**
     * Appends the specified character to this writer.
     *
     * <p> An invocation of this method of the form {@code out.append(c)}
     * behaves in exactly the same way as the invocation
     *
     * <pre>
     *     out.write(c) </pre>
     *
     * @param c The 16-bit character to append
     *
     * @return This writer
     *
     * @since 1.5
     */
    // 将指定的字符写入到输出流
    public StringWriter append(char c) {
        write(c);
        return this;
    }
    
    /**
     * Appends the specified character sequence to this writer.
     *
     * <p> An invocation of this method of the form {@code out.append(csq)}
     * behaves in exactly the same way as the invocation
     *
     * <pre>
     *     out.write(csq.toString()) </pre>
     *
     * <p> Depending on the specification of {@code toString} for the
     * character sequence {@code csq}, the entire sequence may not be
     * appended. For instance, invoking the {@code toString} method of a
     * character buffer will return a subsequence whose content depends upon
     * 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 writer.
     *
     * @return This writer
     *
     * @since 1.5
     */
    // 将字符序列csq的字符写入到输出流
    public StringWriter append(CharSequence csq) {
        write(String.valueOf(csq));
        return this;
    }
    
    /**
     * Appends a subsequence of the specified character sequence to this writer.
     *
     * <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>{@code
     *     out.write(csq.subSequence(start, end).toString())
     * }</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 This writer
     *
     * @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()}
     * @since 1.5
     */
    // 将字符序列csq[start, end)范围的字符写入到输出流
    public StringWriter append(CharSequence csq, int start, int end) {
        if(csq == null) {
            csq = "null";
        }
        return append(csq.subSequence(start, end));
    }
    
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    /**
     * Closing a {@code StringWriter} has no effect. The methods in this
     * class can be called after the stream has been closed without generating
     * an {@code IOException}.
     */
    // 关闭输出流
    public void close() throws IOException {
    }
    
    /**
     * Flush the stream.
     */
    // 将内部缓冲区中的字符写入到输出流
    public void flush() {
    }
    
    
    /**
     * Return the string buffer itself.
     *
     * @return StringBuffer holding the current buffer value.
     */
    // 返回输出流中写入的字符序列
    public StringBuffer getBuffer() {
        return buf;
    }
    
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    /**
     * Return the buffer's current value as a string.
     */
    public String toString() {
        return buf.toString();
    }
    
}