randomaccessfile.java

《移动Agent技术》一书的所有章节源代码。

    public void write(byte b[], int off, int len) throws IOException {
	writeBytes(b, off, len);
    }

    // 'Random access' stuff

    /**
     * Returns the current offset in this file. 
     *
     * @return     the offset from the beginning of the file, in bytes,
     *             at which the next read or write occurs.
     * @exception  IOException  if an I/O error occurs.
     * @since      JDK1.0
     */
    public native long getFilePointer() throws IOException;

    /**
     * Sets the file-pointer offset, measured from the beginning of this 
     * file, at which the next read or write occurs.  The offset may be 
     * set beyond the end of the file. Setting the offset beyond the end 
     * of the file does not change the file length.  The file length will 
     * change only by writing after the offset has been set beyond the end 
     * of the file. 
     *
     * @param      pos   the offset position, measured in bytes from the 
     *                   beginning of the file, at which to set the file 
     *                   pointer.
     * @exception  IOException  if an I/O error occurs.
     * @since      JDK1.0
     */
    public native void seek(long pos) throws IOException;

    /**
     * Returns the length of this file.
     *
     * @return     the length of this file.
     * @exception  IOException  if an I/O error occurs.
     * @since      JDK1.0
     */
    public native long length() throws IOException;

    /**
     * Closes this random access file stream and releases any system 
     * resources associated with the stream. 
     *
     * @exception  IOException  if an I/O error occurs.
     * @since      JDK1.0
     */
    public native void close() throws IOException;

    //
    //  Some "reading/writing Java data types" methods stolen from
    //  DataInputStream and DataOutputStream.
    //

    /**
     * Reads a <code>boolean</code> from this file. This method reads a 
     * single byte from the file. A value of <code>0</code> represents 
     * <code>false</code>. Any other value represents <code>true</code>. 
     * This method blocks until the byte is read, the end of the stream 
     * is detected, or an exception is thrown. 
     *
     * @return     the <code>boolean</code> value read.
     * @exception  EOFException  if this file has reached the end.
     * @exception  IOException   if an I/O error occurs.
     * @since      JDK1.0
     */
    public final boolean readBoolean() throws IOException {
	int ch = this.read();
	if (ch < 0)
	    throw new EOFException();
	return (ch != 0);
    }

    /**
     * Reads a signed 8-bit value from this file. This method reads a 
     * byte from the file. If the byte read is <code>b</code>, where 
     * <code>0&nbsp;&lt;=&nbsp;b&nbsp;&lt;=&nbsp;255</code>, 
     * then the result is:
     * <ul><code>
     *     (byte)(b)
     *</code></ul>
     * <p>
     * This method blocks until the byte is read, the end of the stream 
     * is detected, or an exception is thrown. 
     *
     * @return     the next byte of this file as a signed 8-bit
     *             <code>byte</code>.
     * @exception  EOFException  if this file has reached the end.
     * @exception  IOException   if an I/O error occurs.
     * @since      JDK1.0
     */
    public final byte readByte() throws IOException {
	int ch = this.read();
	if (ch < 0)
	    throw new EOFException();
	return (byte)(ch);
    }

    /**
     * Reads an unsigned 8-bit number from this file. This method reads 
     * a byte from this file and returns that byte. 
     * <p>
     * This method blocks until the byte is read, the end of the stream 
     * is detected, or an exception is thrown. 
     *
     * @return     the next byte of this file, interpreted as an unsigned
     *             8-bit number.
     * @exception  EOFException  if this file has reached the end.
     * @exception  IOException   if an I/O error occurs.
     * @since      JDK1.0
     */
    public final int readUnsignedByte() throws IOException {
	int ch = this.read();
	if (ch < 0)
	    throw new EOFException();
	return ch;
    }

    /**
     * Reads a signed 16-bit number from this file. The method reads 2 
     * bytes from this file. If the two bytes read, in order, are 
     * <code>b1</code> and <code>b2</code>, where each of the two values is 
     * between <code>0</code> and <code>255</code>, inclusive, then the 
     * result is equal to:
     * <ul><code>
     *     (short)((b1 &lt;&lt; 8) | b2)
     * </code></ul>
     * <p>
     * This method blocks until the two bytes are read, the end of the 
     * stream is detected, or an exception is thrown. 
     *
     * @return     the next two bytes of this file, interpreted as a signed
     *             16-bit number.
     * @exception  EOFException  if this file reaches the end before reading
     *               two bytes.
     * @exception  IOException   if an I/O error occurs.
     * @since      JDK1.0
     */
    public final short readShort() throws IOException {
	int ch1 = this.read();
	int ch2 = this.read();
	if ((ch1 | ch2) < 0)
	     throw new EOFException();
	return (short)((ch1 << 8) + (ch2 << 0));
    }

    /**
     * Reads an unsigned 16-bit number from this file. This method reads 
     * two bytes from the file. If the bytes read, in order, are 
     * <code>b1</code> and <code>b2</code>, where 
     * <code>0&nbsp;&lt;=&nbsp;b1, b2&nbsp;&lt;=&nbsp;255</code>, 
     * then the result is equal to:
     * <ul><code>
     *     (b1 &lt;&lt; 8) | b2
     * </code></ul>
     * <p>
     * This method blocks until the two bytes are read, the end of the 
     * stream is detected, or an exception is thrown. 
     *
     * @return     the next two bytes of this file, interpreted as an unsigned
     *             16-bit integer.
     * @exception  EOFException  if this file reaches the end before reading
     *               two bytes.
     * @exception  IOException   if an I/O error occurs.
     * @since      JDK1.0
     */
    public final int readUnsignedShort() throws IOException {
	int ch1 = this.read();
	int ch2 = this.read();
	if ((ch1 | ch2) < 0)
	     throw new EOFException();
	return (ch1 << 8) + (ch2 << 0);
    }

    /**
     * Reads a Unicode character from this file. This method reads two
     * bytes from the file. If the bytes read, in order, are 
     * <code>b1</code> and <code>b2</code>, where 
     * <code>0&nbsp;&lt;=&nbsp;b1,&nbsp;b2&nbsp;&lt;=&nbsp;255</code>, 
     * then the result is equal to:
     * <ul><code>
     *     (char)((b1 &lt;&lt; 8) | b2)
     * </code></ul>
     * <p>
     * This method blocks until the two bytes are read, the end of the 
     * stream is detected, or an exception is thrown. 
     *
     * @return     the next two bytes of this file as a Unicode character.
     * @exception  EOFException  if this file reaches the end before reading
     *               two bytes.
     * @exception  IOException   if an I/O error occurs.
     * @since      JDK1.0
     */
    public final char readChar() throws IOException {
	int ch1 = this.read();
	int ch2 = this.read();
	if ((ch1 | ch2) < 0)
	     throw new EOFException();
	return (char)((ch1 << 8) + (ch2 << 0));
    }

    /**
     * Reads a signed 32-bit integer from this file. This method reads 4 
     * bytes from the file. If the bytes read, in order, are <code>b1</code>,
     * <code>b2</code>, <code>b3</code>, and <code>b4</code>, where 
     * <code>0&nbsp;&lt;=&nbsp;b1, b2, b3, b4&nbsp;&lt;=&nbsp;255</code>, 
     * then the result is equal to:
     * <ul><code>
     *     (b1 &lt;&lt; 24) | (b2 &lt;&lt; 16) + (b3 &lt;&lt; 8) + b4
     * </code></ul>
     * <p>
     * This method blocks until the four bytes are read, the end of the 
     * stream is detected, or an exception is thrown. 
     *
     * @return     the next four bytes of this file, interpreted as an
     *             <code>int</code>.
     * @exception  EOFException  if this file reaches the end before reading
     *               four bytes.
     * @exception  IOException   if an I/O error occurs.
     * @since      JDK1.0
     */
    public final int readInt() throws IOException {
	int ch1 = this.read();
	int ch2 = this.read();
	int ch3 = this.read();
	int ch4 = this.read();
	if ((ch1 | ch2 | ch3 | ch4) < 0)
	     throw new EOFException();
	return ((ch1 << 24) + (ch2 << 16) + (ch3 << 8) + (ch4 << 0));
    }

    /**
     * Reads a signed 64-bit integer from this file. This method reads eight
     * bytes from the file. If the bytes read, in order, are 
     * <code>b1</code>, <code>b2</code>, <code>b3</code>, 
     * <code>b4</code>, <code>b5</code>, <code>b6</code>, 
     * <code>b7</code>, and <code>b8,</code> where:
     * <ul><code>
     *     0 &lt;= b1, b2, b3, b4, b5, b6, b7, b8 &lt;=255,
     * </code></ul>
     * <p>
     * then the result is equal to:
     * <p><blockquote><pre>
     *     ((long)b1 &lt;&lt; 56) + ((long)b2 &lt;&lt; 48)
     *     + ((long)b3 &lt;&lt; 40) + ((long)b4 &lt;&lt; 32)
     *     + ((long)b5 &lt;&lt; 24) + ((long)b6 &lt;&lt; 16)
     *     + ((long)b7 &lt;&lt; 8) + b8
     * </pre></blockquote>
     * <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>long</code>.
     * @exception  EOFException  if this file reaches the end before reading
     *               eight bytes.
     * @exception  IOException   if an I/O error occurs.
     * @since      JDK1.0
     */
    public final long readLong() throws IOException {
	return ((long)(readInt()) << 32) + (readInt() & 0xFFFFFFFFL);
    }

    /**
     * Reads a <code>float</code> from this file. This method reads an 
     * <code>int</code> value as if by the <code>readInt</code> method 
     * and then converts that <code>int</code> to a <code>float</code> 
     * using the <code>intBitsToFloat</code> method in class 
     * <code>Float</code>. 
     * <p>
     * This method blocks until the four bytes are read, the end of the 
     * stream is detected, or an exception is thrown. 
     *
     * @return     the next four bytes of this file, interpreted as a
     *             <code>float</code>.
     * @exception  EOFException  if this file reaches the end before reading
     *             four bytes.
     * @exception  IOException   if an I/O error occurs.
     * @see        java.io.RandomAccessFile#readInt()
     * @see        java.lang.Float#intBitsToFloat(int)
     * @since      JDK1.0
     */
    public final float readFloat() throws IOException {
	return Float.intBitsToFloat(readInt());
    }

    /**
     * Reads a <code>double</code> from this file. This method reads a 
     * <code>long</code> value as if by the <code>readLong</code> method