J2Me学习输入流--ByteAraayInputStream

java.io
Class ByteArrayInputStream

java.lang.Object
  extended byjava.io.InputStream
      extended byjava.io.ByteArrayInputStream

public class ByteArrayInputStream
extends InputStream

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.

Since:
    JDK1.0, CLDC 1.0

Field Summary
protected  byte[] buf
          An array of bytes that was provided by the creator of the stream.
protected  int count
          The index one greater than the last valid character in the input stream buffer.
protected  int mark
          The currently marked position in the stream.
protected  int pos
          The index of the next character to read from the input stream buffer.

Constructor Summary
ByteArrayInputStream(byte[] buf)
          Creates a ByteArrayInputStream so that it uses buf as its buffer array.
ByteArrayInputStream(byte[] buf, int offset, int length)
          Creates ByteArrayInputStream that uses buf as its buffer array.

Method Summary
int available()
          Returns the number of bytes that can be read from this input stream without blocking.
void close()
          Closes this input stream and releases any system resources associated with the stream.
void mark(int readAheadLimit)
          Set the current marked position in the stream.
boolean markSupported()
          Tests if ByteArrayInputStream supports mark/reset.
int read()
          Reads the next byte of data from this input stream.
int read(byte[] b, int off, int len)
          Reads up to len bytes of data into an array of bytes from this input stream.
void reset()
          Resets the buffer to the marked position.
long skip(long n)
          Skips n bytes of input from this input stream.

Methods inherited from class java.io.InputStream
read

Methods inherited from class java.lang.Object
equals, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait


Field Detail
buf

protected byte[] buf

    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.

pos

protected int pos

    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].

mark

protected int mark

    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

count

protected int count

    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.

Constructor Detail
ByteArrayInputStream

public ByteArrayInputStream(byte[] buf)

    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.

Parameters:
    buf - the input buffer.

ByteArrayInputStream

public ByteArrayInputStream(byte[] buf,
                            int offset,
                            int 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.

Parameters:
    buf - the input buffer.
    offset - the offset in the buffer of the first byte to read.
    length - the maximum number of bytes to read from the buffer.

Method Detail
read

public int read()

    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.

    Specified by:
        read in class InputStream

    Returns:
        the next byte of data, or -1 if the end of the stream has been reached.

read

public int read(byte[] b,
                int off,
                int len)

    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.

    Overrides:
        read in class InputStream

    Parameters:
        b - the buffer into which the data is read.
        off - the start offset of the data.
        len - the maximum number of bytes read.
    Returns:
        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.
    See Also:
        InputStream.read()

skip

public long skip(long n)

    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.

    Overrides:
        skip in class InputStream

    Parameters:
        n - the number of bytes to be skipped.
    Returns:
        the actual number of bytes skipped.

available

public int available()

    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.

    Overrides:
        available in class InputStream

    Returns:
        the number of bytes that can be read from the input stream without blocking.

markSupported

public boolean markSupported()

    Tests if ByteArrayInputStream supports mark/reset.

    Overrides:
        markSupported in class InputStream

    Returns:
        true if this true type supports the mark and reset method; false otherwise.
    Since:
        JDK1.1
    See Also:
        InputStream.mark(int), InputStream.reset()

mark

public void mark(int readAheadLimit)

    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.

    Overrides:
        mark in class InputStream

    Parameters:
        readAheadLimit - the maximum limit of bytes that can be read before the mark position becomes invalid.
    Since:
        JDK1.1
    See Also:
        InputStream.reset()

reset

public void reset()

    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.

    Overrides:
        reset in class InputStream

    See Also:
        InputStream.mark(int), IOException

close

public void close()
           throws IOException

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

    Overrides:
        close in class InputStream

    Throws:
        IOException - if an I/O error occurs.