www.pudn.com > j2me_cldc-1_1-fcs-src-winunix.rar > ByteArrayInputStream.java

/*
 * Copyright © 2003 Sun Microsystems, Inc. All rights reserved.
 * SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 *
 */

package java.io;

/**
 * A ByteArrayInputStream contains
 * an internal buffer that contains bytes that
 * may be read from the stream. An internal
 * counter keeps track of the next byte to
 * be supplied by the read method.
 *
 * @author  Arthur van Hoff, Nik Shaylor
 * @version 12/17/01 (CLDC 1.1)
 * @since   JDK1.0, CLDC 1.0
 */
public
class ByteArrayInputStream extends InputStream {

    /**
     * An array of bytes that was provided
     * by the creator of the stream. Elements buf[0]
     * through buf[count-1] are the
     * only bytes that can ever be read from the
     * stream;  element buf[pos] is
     * the next byte to be read.
     */
    protected byte buf[];

    /**
     * The index of the next character to read from the input stream buffer.
     * This value should always be nonnegative
     * and not larger than the value of count.
     * The next byte to be read from the input stream buffer
     * will be buf[pos].
     */
    protected int pos;

    /**
     * The currently marked position in the stream.
     * ByteArrayInputStream objects are marked at position zero by
     * default when constructed.  They may be marked at another
     * position within the buffer by the mark() method.
     * The current buffer position is set to this point by the
     * reset() method.
     *
     * @since   JDK1.1
     */
    protected int mark = 0;

    /**
     * The index one greater than the last valid character in the input
     * stream buffer.
     * This value should always be nonnegative
     * and not larger than the length of buf.
     * It  is one greater than the position of
     * the last byte within buf that
     * can ever be read  from the input stream buffer.
     */
    protected int count;

    /**
     * Creates a ByteArrayInputStream
     * so that it  uses buf as its
     * buffer array.
     * The buffer array is not copied.
     * The initial value of pos
     * is 0 and the initial value
     * of  count is the length of
     * buf.
     *
     * @param   buf   the input buffer.
     */
    public ByteArrayInputStream(byte buf[]) {
        this.buf = buf;
        this.pos = 0;
        this.count = buf.length;
    }

    /**
     * Creates ByteArrayInputStream
     * that uses buf as its
     * buffer array. The initial value of pos
     * is offset and the initial value
     * of count is offset+length.
     * The buffer array is not copied.
     * 

     * Note that if bytes are simply read from
     * the resulting input stream, elements buf[pos]
     * through buf[pos+len-1] will
     * be read; however, if a reset
     * operation  is performed, then bytes buf[0]
     * through buf[pos-1] will then
     * become available for input.
     *
     * @param   buf      the input buffer.
     * @param   offset   the offset in the buffer of the first byte to read.
     * @param   length   the maximum number of bytes to read from the buffer.
     */
    public ByteArrayInputStream(byte buf[], int offset, int length) {
        this.buf = buf;
        this.pos = offset;
        this.count = Math.min(offset + length, buf.length);
        this.mark = offset;
    }

    /**
     * Reads the next byte of data from this input stream. The value
     * byte is returned as an int in the range
     * 0 to 255. If no byte is available
     * because the end of the stream has been reached, the value
     * -1 is returned.
     * 

     * This read method
     * cannot block.
     *
     * @return  the next byte of data, or -1 if the end of the
     *          stream has been reached.
     */
    public synchronized int read() {
        return (pos < count) ? (buf[pos++] & 0xff) : -1;
    }

    /**
     * Reads up to len bytes of data into an array of bytes
     * from this input stream.
     * If pos equals count,
     * then -1 is returned to indicate
     * end of file. Otherwise, the  number k
     * of bytes read is equal to the smaller of
     * len and count-pos.
     * If k is positive, then bytes
     * buf[pos] through buf[pos+k-1]
     * are copied into b[off]  through
     * b[off+k-1] in the manner performed
     * by System.arraycopy. The
     * value k is added into pos
     * and k is returned.
     * 

     * This read method cannot block.
     *
     * @param   b     the buffer into which the data is read.
     * @param   off   the start offset of the data.
     * @param   len   the maximum number of bytes read.
     * @return  the total number of bytes read into the buffer, or
     *          -1 if there is no more data because the end of
     *          the stream has been reached.
     */
    public synchronized int read(byte b[], int off, int len) {
        if (b == null) {
            throw new NullPointerException();
        } else if ((off < 0) || (off > b.length) || (len < 0) ||
                   ((off + len) > b.length) || ((off + len) < 0)) {
            throw new IndexOutOfBoundsException();
        }
        if (pos >= count) {
            return -1;
        }
        if (pos + len > count) {
            len = count - pos;
        }
        if (len <= 0) {
            return 0;
        }
        System.arraycopy(buf, pos, b, off, len);
        pos += len;
        return len;
    }

    /**
     * Skips n bytes of input from this input stream. Fewer
     * bytes might be skipped if the end of the input stream is reached.
     * The actual number k
     * of bytes to be skipped is equal to the smaller
     * of n and  count-pos.
     * The value k is added into pos
     * and k is returned.
     *
     * @param   n   the number of bytes to be skipped.
     * @return  the actual number of bytes skipped.
     */
    public synchronized long skip(long n) {
        if (pos + n > count) {
            n = count - pos;
        }
        if (n < 0) {
            return 0;
        }
        pos += n;
        return n;
    }

    /**
     * Returns the number of bytes that can be read from this input
     * stream without blocking.
     * The value returned is
     * count - pos,
     * which is the number of bytes remaining to be read from the input buffer.
     *
     * @return  the number of bytes that can be read from the input stream
     *          without blocking.
     */
    public synchronized int available() {
        return count - pos;
    }

    /**
     * Tests if ByteArrayInputStream supports mark/reset.
     *
     * @since   JDK1.1
     */
    public boolean markSupported() {
        return true;
    }

    /**
     * Set the current marked position in the stream.
     * ByteArrayInputStream objects are marked at position zero by
     * default when constructed.  They may be marked at another
     * position within the buffer by this method.
     *
     * @since   JDK1.1
     */
    public void mark(int readAheadLimit) {
        mark = pos;
    }

    /**
     * Resets the buffer to the marked position.  The marked position
     * is the beginning unless another position was marked.
     * The value of pos is set to 0.
     */
    public synchronized void reset() {
        pos = mark;
    }

    /**
     * Closes this input stream and releases any system resources
     * associated with the stream.
     * 

     */
    public synchronized void close() throws IOException {
    }

}