randomaccessfile.java

《移动Agent技术》一书的所有章节源代码。

     * and then converts that <code>long</code> to a <code>double</code> 
     * using the <code>longBitsToDouble</code> method in 
     * class <code>Double</code>.
     * <p>
     * This method blocks until the eight bytes are read, the end of the 
     * stream is detected, or an exception is thrown. 
     *
     * @return     the next eight bytes of this file, interpreted as a
     *             <code>double</code>.
     * @exception  EOFException  if this file reaches the end before reading
     *             eight bytes.
     * @exception  IOException   if an I/O error occurs.
     * @see        java.io.RandomAccessFile#readLong()
     * @see        java.lang.Double#longBitsToDouble(long)
     * @since      JDK1.0
     */
    public final double readDouble() throws IOException {
	return Double.longBitsToDouble(readLong());
    }

    /**
     * Reads the next line of text from this file. This method 
     * successively reads bytes from the file until it reaches the end of 
     * a line of text. 
     * <p>
     * A line of text is terminated by a carriage-return character 
     * (<code>'&#92;r'</code>), a newline character (<code>'&#92;n'</code>), a 
     * carriage-return character immediately followed by a newline 
     * character, or the end of the input stream. The line-terminating 
     * character(s), if any, are included as part of the string returned. 
     * <p>
     * This method blocks until a newline character is read, a carriage 
     * return and the byte following it are read (to see if it is a 
     * newline), the end of the stream is detected, or an exception is thrown.
     *
     * @return     the next line of text from this file.
     * @exception  IOException  if an I/O error occurs.
     * @since      JDK1.0
     */
    public final String readLine() throws IOException {
	StringBuffer input = new StringBuffer();
	int c;

	while (((c = read()) != -1) && (c != '\n')) {
	    input.append((char)c);
	}
	if ((c == -1) && (input.length() == 0)) {
	    return null;
	}
	return input.toString();
    }

    /**
     * Reads in a string from this file. The string has been encoded 
     * using a modified UTF-8 format. 
     * <p>
     * The first two bytes are read as if by 
     * <code>readUnsignedShort</code>. This value gives the number of 
     * following bytes that are in the encoded string, not
     * the length of the resulting string. The following bytes are then 
     * interpreted as bytes encoding characters in the UTF-8 format 
     * and are converted into characters. 
     * <p>
     * This method blocks until all the bytes are read, the end of the 
     * stream is detected, or an exception is thrown. 
     *
     * @return     a Unicode string.
     * @exception  EOFException            if this file reaches the end before
     *               reading all the bytes.
     * @exception  IOException             if an I/O error occurs.
     * @exception  UTFDataFormatException  if the bytes do not represent 
     *               valid UTF-8 encoding of a Unicode string.
     * @see        java.io.RandomAccessFile#readUnsignedShort()
     * @since      JDK1.0
     */
    public final String readUTF() throws IOException {
	return DataInputStream.readUTF(this);
    }

    /**
     * Writes a <code>boolean</code> to the file as a 1-byte value. The 
     * value <code>true</code> is written out as the value 
     * <code>(byte)1</code>; the value <code>false</code> is written out 
     * as the value <code>(byte)0</code>.
     *
     * @param      v   a <code>boolean</code> value to be written.
     * @exception  IOException  if an I/O error occurs.
     * @since      JDK1.0
     */
    public final void writeBoolean(boolean v) throws IOException {
	write(v ? 1 : 0);
	//written++;
    }

    /**
     * Writes a <code>byte</code> to the file as a 1-byte value. 
     *
     * @param      v   a <code>byte</code> value to be written.
     * @exception  IOException  if an I/O error occurs.
     * @since      JDK1.0
     */
    public final void writeByte(int v) throws IOException {
	write(v);
	//written++;
    }

    /**
     * Writes a <code>short</code> to the file as two bytes, high byte first.
     *
     * @param      v   a <code>short</code> to be written.
     * @exception  IOException  if an I/O error occurs.
     * @since      JDK1.0
     */
    public final void writeShort(int v) throws IOException {
	write((v >>> 8) & 0xFF);
	write((v >>> 0) & 0xFF);
	//written += 2;
    }

    /**
     * Writes a <code>char</code> to the file as a 2-byte value, high
     * byte first.
     *
     * @param      v   a <code>char</code> value to be written.
     * @exception  IOException  if an I/O error occurs.
     * @since      JDK1.0
     */
    public final void writeChar(int v) throws IOException {
	write((v >>> 8) & 0xFF);
	write((v >>> 0) & 0xFF);
	//written += 2;
    }

    /**
     * Writes an <code>int</code> to the file as four bytes, high byte first.
     *
     * @param      v   an <code>int</code> to be written.
     * @exception  IOException  if an I/O error occurs.
     * @since      JDK1.0
     */
    public final void writeInt(int v) throws IOException {
	write((v >>> 24) & 0xFF);
	write((v >>> 16) & 0xFF);
	write((v >>>  8) & 0xFF);
	write((v >>>  0) & 0xFF);
	//written += 4;
    }

    /**
     * Writes a <code>long</code> to the file as eight bytes, high byte first.
     *
     * @param      v   a <code>long</code> to be written.
     * @exception  IOException  if an I/O error occurs.
     * @since      JDK1.0
     */
    public final void writeLong(long v) throws IOException {
	write((int)(v >>> 56) & 0xFF);
	write((int)(v >>> 48) & 0xFF);
	write((int)(v >>> 40) & 0xFF);
	write((int)(v >>> 32) & 0xFF);
	write((int)(v >>> 24) & 0xFF);
	write((int)(v >>> 16) & 0xFF);
	write((int)(v >>>  8) & 0xFF);
	write((int)(v >>>  0) & 0xFF);
	//written += 8;
    }

    /**
     * Converts the float argument to an <code>int</code> using the 
     * <code>floatToIntBits</code> method in class <code>Float</code>, 
     * and then writes that <code>int</code> value to the file as a 
     * 4-byte quantity, high byte first. 
     *
     * @param      v   a <code>float</code> value to be written.
     * @exception  IOException  if an I/O error occurs.
     * @see        java.lang.Float#floatToIntBits(float)
     * @since      JDK1.0
     */
    public final void writeFloat(float v) throws IOException {
	writeInt(Float.floatToIntBits(v));
    }

    /**
     * Converts the double argument to a <code>long</code> using the 
     * <code>doubleToLongBits</code> method in class <code>Double</code>, 
     * and then writes that <code>long</code> value to the file as an 
     * 8-byte quantity, high byte first. 
     *
     * @param      v   a <code>double</code> value to be written.
     * @exception  IOException  if an I/O error occurs.
     * @see        java.lang.Double#doubleToLongBits(double)
     * @since      JDK1.0
     */
    public final void writeDouble(double v) throws IOException {
	writeLong(Double.doubleToLongBits(v));
    }

    /**
     * Writes the string to the file as a sequence of bytes. Each 
     * character in the string is written out, in sequence, by discarding 
     * its high eight bits. 
     *
     * @param      s   a string of bytes to be written.
     * @exception  IOException  if an I/O error occurs.
     * @since      JDK1.0
     */
    public final void writeBytes(String s) throws IOException {
	int len = s.length();
	byte[] b = new byte[len];
	s.getBytes(0, len, b, 0);
	writeBytes(b, 0, len);
    }

    /**
     * Writes a string to the file as a sequence of characters. Each 
     * character is written to the data output stream as if by the 
     * <code>writeChar</code> method. 
     *
     * @param      s   a <code>String</code> value to be written.
     * @exception  IOException  if an I/O error occurs.
     * @see        java.io.RandomAccessFile#writeChar(int)
     * @since      JDK1.0
     */
    public final void writeChars(String s) throws IOException {
	int clen = s.length();
	int blen = 2*clen;
	byte[] b = new byte[blen];
	char[] c = new char[clen];
	s.getChars(0, clen, c, 0);
	for (int i = 0, j = 0; i < clen; i++) {
	    b[j++] = (byte)(c[i] >>> 8);
	    b[j++] = (byte)(c[i] >>> 0);
	}
	writeBytes(b, 0, blen);
    }

    /**
     * Writes a string to the file using UTF-8 encoding in a 
     * machine-independent manner. 
     * <p>
     * First, two bytes are written to the file as if by the 
     * <code>writeShort</code> method giving the number of bytes to 
     * follow. This value is the number of bytes actually written out, 
     * not the length of the string. Following the length, each character 
     * of the string is output, in sequence, using the UTF-8 encoding 
     * for each character. 
     *
     * @param      str   a string to be written.
     * @exception  IOException  if an I/O error occurs.
     * @since      JDK1.0
     */
    public final void writeUTF(String str) throws IOException {
	int strlen = str.length();
	int utflen = 0;

	for (int i = 0 ; i < strlen ; i++) {
	    int c = str.charAt(i);
	    if ((c >= 0x0001) && (c <= 0x007F)) {
		utflen++;
	    } else if (c > 0x07FF) {
		utflen += 3;
	    } else {
		utflen += 2;
	    }
	}

	if (utflen > 65535)
	    throw new UTFDataFormatException();		  

	write((utflen >>> 8) & 0xFF);
	write((utflen >>> 0) & 0xFF);
	for (int i = 0 ; i < strlen ; i++) {
	    int c = str.charAt(i);
	    if ((c >= 0x0001) && (c <= 0x007F)) {
		write(c);
	    } else if (c > 0x07FF) {
		write(0xE0 | ((c >> 12) & 0x0F));
		write(0x80 | ((c >>  6) & 0x3F));
		write(0x80 | ((c >>  0) & 0x3F));
		//written += 2;
	    } else {
		write(0xC0 | ((c >>  6) & 0x1F));
		write(0x80 | ((c >>  0) & 0x3F));
		//written += 1;
	    }
	}
	//written += strlen + 2;
    }
}