DataOutput.java

/*
 * Copyright (c) 1995, 2013, 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;

/**
 * The <code>DataOutput</code> interface provides
 * for converting data from any of the Java
 * primitive types to a series of bytes and
 * writing these bytes to a binary stream.
 * There is  also a facility for converting
 * a <code>String</code> into
 * <a href="DataInput.html#modified-utf-8">modified UTF-8</a>
 * format and writing the resulting series
 * of bytes.
 * <p>
 * For all the methods in this interface that
 * write bytes, it is generally true that if
 * a byte cannot be written for any reason,
 * an <code>IOException</code> is thrown.
 *
 * @author Frank Yellin
 * @see java.io.DataInput
 * @see java.io.DataOutputStream
 * @since 1.0
 */
// 字节数据输出接口
public interface DataOutput {
    
    /**
     * Writes a <code>boolean</code> value to this output stream.
     * If the argument <code>v</code>
     * is <code>true</code>, the value <code>(byte)1</code>
     * is written; if <code>v</code> is <code>false</code>,
     * the  value <code>(byte)0</code> is written.
     * The byte written by this method may
     * be read by the <code>readBoolean</code>
     * method of interface <code>DataInput</code>,
     * which will then return a <code>boolean</code>
     * equal to <code>v</code>.
     *
     * @param v the boolean to be written.
     *
     * @throws IOException if an I/O error occurs.
     */
    // 向包装的输出流写入boolean值
    void writeBoolean(boolean v) throws IOException;
    
    /**
     * Writes a <code>char</code> value, which
     * is comprised of two bytes, to the
     * output stream.
     * The byte values to be written, in the  order
     * shown, are:
     * <pre>{@code
     * (byte)(0xff & (v >> 8))
     * (byte)(0xff & v)
     * }</pre><p>
     * The bytes written by this method may be
     * read by the <code>readChar</code> method
     * of interface <code>DataInput</code> , which
     * will then return a <code>char</code> equal
     * to <code>(char)v</code>.
     *
     * @param v the <code>char</code> value to be written.
     *
     * @throws IOException if an I/O error occurs.
     */
    // 向包装的输出流写入char值（按大端法写入）
    void writeChar(int v) throws IOException;
    
    /**
     * Writes to the output stream the eight low-
     * order bits of the argument <code>v</code>.
     * The 24 high-order bits of <code>v</code>
     * are ignored. (This means  that <code>writeByte</code>
     * does exactly the same thing as <code>write</code>
     * for an integer argument.) The byte written
     * by this method may be read by the <code>readByte</code>
     * method of interface <code>DataInput</code>,
     * which will then return a <code>byte</code>
     * equal to <code>(byte)v</code>.
     *
     * @param v the byte value to be written.
     *
     * @throws IOException if an I/O error occurs.
     */
    // 向包装的输出流写入byte值
    void writeByte(int v) throws IOException;
    
    /**
     * Writes two bytes to the output
     * stream to represent the value of the argument.
     * The byte values to be written, in the  order
     * shown, are:
     * <pre>{@code
     * (byte)(0xff & (v >> 8))
     * (byte)(0xff & v)
     * }</pre> <p>
     * The bytes written by this method may be
     * read by the <code>readShort</code> method
     * of interface <code>DataInput</code> , which
     * will then return a <code>short</code> equal
     * to <code>(short)v</code>.
     *
     * @param v the <code>short</code> value to be written.
     *
     * @throws IOException if an I/O error occurs.
     */
    // 向包装的输出流写入short值（按大端法写入）
    void writeShort(int v) throws IOException;
    
    /**
     * Writes an <code>int</code> value, which is
     * comprised of four bytes, to the output stream.
     * The byte values to be written, in the  order
     * shown, are:
     * <pre>{@code
     * (byte)(0xff & (v >> 24))
     * (byte)(0xff & (v >> 16))
     * (byte)(0xff & (v >>  8))
     * (byte)(0xff & v)
     * }</pre><p>
     * The bytes written by this method may be read
     * by the <code>readInt</code> method of interface
     * <code>DataInput</code> , which will then
     * return an <code>int</code> equal to <code>v</code>.
     *
     * @param v the <code>int</code> value to be written.
     *
     * @throws IOException if an I/O error occurs.
     */
    // 向包装的输出流写入int值（按大端法写入）
    void writeInt(int v) throws IOException;
    
    /**
     * Writes a <code>long</code> value, which is
     * comprised of eight bytes, to the output stream.
     * The byte values to be written, in the  order
     * shown, are:
     * <pre>{@code
     * (byte)(0xff & (v >> 56))
     * (byte)(0xff & (v >> 48))
     * (byte)(0xff & (v >> 40))
     * (byte)(0xff & (v >> 32))
     * (byte)(0xff & (v >> 24))
     * (byte)(0xff & (v >> 16))
     * (byte)(0xff & (v >>  8))
     * (byte)(0xff & v)
     * }</pre><p>
     * The bytes written by this method may be
     * read by the <code>readLong</code> method
     * of interface <code>DataInput</code> , which
     * will then return a <code>long</code> equal
     * to <code>v</code>.
     *
     * @param v the <code>long</code> value to be written.
     *
     * @throws IOException if an I/O error occurs.
     */
    // 向包装的输出流写入long值（按大端法写入）
    void writeLong(long v) throws IOException;
    
    /**
     * Writes a <code>float</code> value,
     * which is comprised of four bytes, to the output stream.
     * It does this as if it first converts this
     * <code>float</code> value to an <code>int</code>
     * in exactly the manner of the <code>Float.floatToIntBits</code>
     * method  and then writes the <code>int</code>
     * value in exactly the manner of the  <code>writeInt</code>
     * method.  The bytes written by this method
     * may be read by the <code>readFloat</code>
     * method of interface <code>DataInput</code>,
     * which will then return a <code>float</code>
     * equal to <code>v</code>.
     *
     * @param v the <code>float</code> value to be written.
     *
     * @throws IOException if an I/O error occurs.
     */
    // 向包装的输出流写入float值（先转为二进制，再按大端法写入）
    void writeFloat(float v) throws IOException;
    
    /**
     * Writes a <code>double</code> value,
     * which is comprised of eight bytes, to the output stream.
     * It does this as if it first converts this
     * <code>double</code> value to a <code>long</code>
     * in exactly the manner of the <code>Double.doubleToLongBits</code>
     * method  and then writes the <code>long</code>
     * value in exactly the manner of the  <code>writeLong</code>
     * method. The bytes written by this method
     * may be read by the <code>readDouble</code>
     * method of interface <code>DataInput</code>,
     * which will then return a <code>double</code>
     * equal to <code>v</code>.
     *
     * @param v the <code>double</code> value to be written.
     *
     * @throws IOException if an I/O error occurs.
     */
    // 向包装的输出流写入double值（先转为二进制，按大端法写入）
    void writeDouble(double v) throws IOException;
    
    /**
     * Writes a string to the output stream.
     * For every character in the string
     * <code>s</code>,  taken in order, one byte
     * is written to the output stream.  If
     * <code>s</code> is <code>null</code>, a <code>NullPointerException</code>
     * is thrown.<p>  If <code>s.length</code>
     * is zero, then no bytes are written. Otherwise,
     * the character <code>s[0]</code> is written
     * first, then <code>s[1]</code>, and so on;
     * the last character written is <code>s[s.length-1]</code>.
     * For each character, one byte is written,
     * the low-order byte, in exactly the manner
     * of the <code>writeByte</code> method . The
     * high-order eight bits of each character
     * in the string are ignored.
     *
     * @param s the string of bytes to be written.
     *
     * @throws IOException if an I/O error occurs.
     */
    // 向包装的输出流写入String值(按字节写入)
    void writeBytes(String s) throws IOException;
    
    /**
     * Writes every character in the string <code>s</code>,
     * to the output stream, in order,
     * two bytes per character. If <code>s</code>
     * is <code>null</code>, a <code>NullPointerException</code>
     * is thrown.  If <code>s.length</code>
     * is zero, then no characters are written.
     * Otherwise, the character <code>s[0]</code>
     * is written first, then <code>s[1]</code>,
     * and so on; the last character written is
     * <code>s[s.length-1]</code>. For each character,
     * two bytes are actually written, high-order
     * byte first, in exactly the manner of the
     * <code>writeChar</code> method.
     *
     * @param s the string value to be written.
     *
     * @throws IOException if an I/O error occurs.
     */
    // 向包装的输出流写入String值(按字符写入)
    void writeChars(String s) throws IOException;
    
    /**
     * Writes two bytes of length information
     * to the output stream, followed
     * by the
     * <a href="DataInput.html#modified-utf-8">modified UTF-8</a>
     * representation
     * of  every character in the string <code>s</code>.
     * If <code>s</code> is <code>null</code>,
     * a <code>NullPointerException</code> is thrown.
     * Each character in the string <code>s</code>
     * is converted to a group of one, two, or
     * three bytes, depending on the value of the
     * character.<p>
     * If a character <code>c</code>
     * is in the range <code>&#92;u0001</code> through
     * <code>&#92;u007f</code>, it is represented
     * by one byte:
     * <pre>(byte)c </pre>  <p>
     * If a character <code>c</code> is <code>&#92;u0000</code>
     * or is in the range <code>&#92;u0080</code>
     * through <code>&#92;u07ff</code>, then it is
     * represented by two bytes, to be written
     * in the order shown: <pre>{@code
     * (byte)(0xc0 | (0x1f & (c >> 6)))
     * (byte)(0x80 | (0x3f & c))
     * }</pre> <p> If a character
     * <code>c</code> is in the range <code>&#92;u0800</code>
     * through <code>uffff</code>, then it is
     * represented by three bytes, to be written
     * in the order shown: <pre>{@code
     * (byte)(0xe0 | (0x0f & (c >> 12)))
     * (byte)(0x80 | (0x3f & (c >>  6)))
     * (byte)(0x80 | (0x3f & c))
     * }</pre>  <p> First,
     * the total number of bytes needed to represent
     * all the characters of <code>s</code> is
     * calculated. If this number is larger than
     * <code>65535</code>, then a <code>UTFDataFormatException</code>
     * is thrown. Otherwise, this length is written
     * to the output stream in exactly the manner
     * of the <code>writeShort</code> method;
     * after this, the one-, two-, or three-byte
     * representation of each character in the
     * string <code>s</code> is written.<p>  The
     * bytes written by this method may be read
     * by the <code>readUTF</code> method of interface
     * <code>DataInput</code> , which will then
     * return a <code>String</code> equal to <code>s</code>.
     *
     * @param s the string value to be written.
     *
     * @throws IOException if an I/O error occurs.
     */
    // 将String按UTF8编码后写入当前输出流
    void writeUTF(String s) throws IOException;
    
    
    /**
     * Writes to the output stream the eight
     * low-order bits of the argument <code>b</code>.
     * The 24 high-order  bits of <code>b</code>
     * are ignored.
     *
     * @param b the byte to be written.
     *
     * @throws IOException if an I/O error occurs.
     */
    // 向包装的输出流写入一个byte
    void write(int b) throws IOException;
    
    /**
     * Writes to the output stream all the bytes in array <code>b</code>.
     * If <code>b</code> is <code>null</code>,
     * a <code>NullPointerException</code> is thrown.
     * If <code>b.length</code> is zero, then
     * no bytes are written. Otherwise, the byte
     * <code>b[0]</code> is written first, then
     * <code>b[1]</code>, and so on; the last byte
     * written is <code>b[b.length-1]</code>.
     *
     * @param b the data.
     *
     * @throws IOException if an I/O error occurs.
     */
    // 向包装的输出流写入b中全部字节
    void write(byte[] b) throws IOException;
    
    /**
     * Writes <code>len</code> bytes from array
     * <code>b</code>, in order,  to
     * the output stream.  If <code>b</code>
     * is <code>null</code>, a <code>NullPointerException</code>
     * is thrown.  If <code>off</code> is negative,
     * or <code>len</code> is negative, or <code>off+len</code>
     * is greater than the length of the array
     * <code>b</code>, then an <code>IndexOutOfBoundsException</code>
     * is thrown.  If <code>len</code> is zero,
     * then no bytes are written. Otherwise, the
     * byte <code>b[off]</code> is written first,
     * then <code>b[off+1]</code>, and so on; the
     * last byte written is <code>b[off+len-1]</code>.
     *
     * @param b   the data.
     * @param off the start offset in the data.
     * @param len the number of bytes to write.
     *
     * @throws IOException if an I/O error occurs.
     */
    // 向包装的输出流写入b中off处起的len个byte
    void write(byte[] b, int off, int len) throws IOException;
    
}