java.io
Class InputStream

java.lang.Object
  java.io.InputStream

Direct Known Subclasses:

FilterInputStream

public abstract class InputStream
extends Object

This abstract class forms the base of the hierarchy of classes that read input as a stream of bytes. It provides a common set of methods for reading bytes from streams. Subclasses implement and extend these methods to read bytes from a particular input source such as a file or network connection.

Constructor Summary

InputStream()
Default, no-arg, public constructor

Method Summary

int	available() This method returns the number of bytes that can be read from this stream before a read can block.
void	close() This method closes the stream.
void	mark(int readLimit) This method marks a position in the input to which the stream can be "reset" by calling the reset() method.
boolean	markSupported() This method returns a boolean that indicates whether the mark/reset methods are supported in this class.
abstract int	read() This method reads an unsigned byte from the input stream and returns it as an int in the range of 0-255.
int	read(byte[] b) This method reads bytes from a stream and stores them into a caller supplied buffer.
int	read(byte[] b, int off, int len) This method read bytes from a stream and stores them into a caller supplied buffer.
void	reset() This method resets a stream to the point where the mark() method was called.
long	skip(long n) This method skips the specified number of bytes in the stream.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

InputStream

public InputStream()

Default, no-arg, public constructor

Method Detail

available

public int available()
              throws IOException

This method returns the number of bytes that can be read from this stream before a read can block. A return of 0 indicates that blocking might (or might not) occur on the very next read attempt.

This method always returns 0 in this class

Returns:

The number of bytes that can be read before blocking could occur

Throws:

IOException - If an error occurs

close

public void close()
           throws IOException

This method closes the stream. Any futher attempts to read from the stream may generate an IOException

This method does nothing in this class, but subclasses may override this method in order to provide additional functionality.

Throws:

IOException - If an error occurs, which can only happen in a subclass

mark

public void mark(int readLimit)

This method marks a position in the input to which the stream can be "reset" by calling the reset() method. The parameter @code{readlimit} is the number of bytes that can be read from the stream after setting the mark before the mark becomes invalid. For example, if mark() is called with a read limit of 10, then when 11 bytes of data are read from the stream before the reset() method is called, then the mark is invalid and the stream object instance is not required to remember the mark.

This method does nothing in this class, but subclasses may override it to provide mark/reset functionality.

Parameters:

readLimit - The number of bytes that can be read before the mark becomes invalid

markSupported

public boolean markSupported()

This method returns a boolean that indicates whether the mark/reset methods are supported in this class. Those methods can be used to remember a specific point in the stream and reset the stream to that point.

This method always returns false in this class, but subclasses can override this method to return true if they support mark/reset functionality.

Returns:

true if mark/reset functionality is supported, false otherwise

read

public abstract int read()
                  throws IOException

This method reads an unsigned byte from the input stream and returns it as an int in the range of 0-255. This method also will return -1 if the end of the stream has been reached.

This method will block until the byte can be read.

Returns:

The byte read or -1 if end of stream

Throws:

IOException - If an error occurs

read

public int read(byte[] b)
         throws IOException

This method reads bytes from a stream and stores them into a caller supplied buffer. This method attempts to completely fill the buffer, but can return before doing so. The actual number of bytes read is returned as an int. A -1 is returned to indicate the end of the stream.

This method will block until some data can be read.

This method operates by calling an overloaded read method like so: read(b, 0, b.length)

Parameters:

b - The buffer into which the bytes read will be stored.

Returns:

The number of bytes read or -1 if end of stream.

Throws:

IOException - If an error occurs.

read

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

This method read bytes from a stream and stores them into a caller supplied buffer. It starts storing the data at index off into the buffer and attempts to read len bytes. This method can return before reading the number of bytes requested. The actual number of bytes read is returned as an int. A -1 is returned to indicate the end of the stream.

This method will block until some data can be read.

This method operates by calling the single byte read() method in a loop until the desired number of bytes are read. The read loop stops short if the end of the stream is encountered or if an IOException is encountered on any read operation except the first. If the first attempt to read a bytes fails, the IOException is allowed to propagate upward. And subsequent IOException is caught and treated identically to an end of stream condition. Subclasses can (and should if possible) override this method to provide a more efficient implementation.

Parameters:

b - The array into which the bytes read should be stored

off - The offset into the array to start storing bytes

len - The requested number of bytes to read

Returns:

The actual number of bytes read, or -1 if end of stream.

Throws:

IOException - If an error occurs.

reset

public void reset()
           throws IOException

This method resets a stream to the point where the mark() method was called. Any bytes that were read after the mark point was set will be re-read during subsequent reads.

This method always throws an IOException in this class, but subclasses can override this method if they provide mark/reset functionality.

Throws:

IOException - Always thrown for this class

skip

public long skip(long n)
          throws IOException

This method skips the specified number of bytes in the stream. It returns the actual number of bytes skipped, which may be less than the requested amount.

This method reads and discards bytes into a byte array until the specified number of bytes were skipped or until either the end of stream is reached or a read attempt returns a short count. Subclasses can override this method to provide a more efficient implementation where one exists.

Parameters:

n - The requested number of bytes to skip

Returns:

The actual number of bytes skipped.

Throws:

IOException - If an error occurs