Chapter 11
The java.io Package

BufferedOutputStream

Name

Synopsis

Class Name:

java.io.BufferedOutputStream

Superclass:

java.io.FilterOutputStream

Immediate Subclasses:

None

Interfaces Implemented:

None

Availability:

JDK 1.0 or later

A BufferedOutputStream object provides a more efficient way to write just a few bytes at a time to an OutputStream. BufferedOutputStream objects use a buffer to store output for an associated OutputStream. In other words, a large number of bytes are stored in an internal buffer and only written when the buffer fills up or is explicitly flushed. A BufferedOutputStream is more efficient than a regular OutputStream because the data is written to memory, rather than a disk or a network. Minimizing the number of write operations to a disk or the network minimizes the cumulative overhead for these operations.

You should wrap a BufferedOutputStream around any OutputStream whose write() operations may be time consuming or costly, such as a FileOutputStream.

Class Summary

public class java.io.BufferedOutputStream 
             extends java.io.FilterOutputStream {
  // Variables
  protected byte[] buf;
  protected int count;
  // Constructors
  public BufferedOutputStream(OutputStream out);
  public BufferedOutputStream(OutputStream out, int size);
  // Instance Methods
  public synchronized void flush();
  public synchronized void write(int b);
  public synchronized void write(byte[] b, int off, int len);
}

Variables

buf

protected byte[] buf

Description: The buffer that stores the data for the output stream.

count

protected int count

Description: The current position in the buffer.

Constructors

BufferedOutputStream

public BufferedOutputStream(OutputStream out)

Parameters

out: The output stream to buffer.

Description

This constructor creates a BufferedOutputStream that acts on the specified OutputStream, using a buffer with the default size of 512 bytes.

public BufferedOutputStream(OutputStream out, int size)

Parameters

out

The output stream to buffer.

size

The size of buffer to use.

Description

This constructor creates a BufferedOutputStream that acts on the specified OutputStream, using a buffer that is size bytes long.

Instance Methods

flush

public synchronized void flush() throws IOException

Throws

IOException: If any kind of I/O error occurs.

Overrides

FilterOutputStream.flush()

Description

This method writes the contents of the buffer to the underlying output stream. It is called automatically when the buffer fills up. You can also call it before the buffer is full. This is known as "flushing" the buffer. This method blocks until the underlying write() is complete.

write

public synchronized void write(int b) throws IOException

Parameters

b: The value to write.

Throws

IOException: If any kind of I/O error occurs.

Overrides

FilterOutputStream.write(int)

Description

This method places a byte containing the low-order eight bits of the given integer into the buffer. If the buffer is full, it is flushed, and the value b is placed in the newly empty buffer. If the buffer is flushed, this method blocks until flush() returns; otherwise this method returns immediately.

 public synchronized void write(byte b[], int off, int len) throws IOException

Parameters

b

An array of bytes to write to the stream.

off

An offset into the byte array.

len

The number of bytes to write.

Throws

IOException: If any kind of I/O error occurs.

Overrides

FilterOutputStream.write(byte[], int, int)

Description

This method copies len bytes from b, starting at off, into the buffer. If there is enough space left in the buffer for the new data, it is copied into the buffer and the method returns immediately. Otherwise, the buffer is flushed, and the new data is written directly to the underlying stream. This is subtly different from the behavior of write(int), which places new data in the buffer after a flush().

Inherited Methods

Method	Inherited From	Method	Inherited From
`clone()`	`Object`	`close()`	`FilterOutputStream`
`equals(Object)`	`Object`	`finalize()`	`Object`
`getClass()`	`Object`	`hashCode()`	`Object`
`notify()`	`Object`	`notifyAll()`	`Object`
`toString()`	`Object`	`wait()`	`Object`
`wait(long)`	`Object`	`wait(long, int)`	`Object`
`write(byte[])`	`FilterOutputStream`