OutputStream (Java SE 22 & JDK 22)
Description: declaration: module: java.base, package: java.io, class: OutputStream
Keywords: java.io.OutputStream class

Module java.base
Package java.io

# Class OutputStream

java.lang.Object
java.io.OutputStream

All Implemented Interfaces:
  `Closeable`, `Flushable`, `AutoCloseable`

Direct Known Subclasses:
  `ByteArrayOutputStream`, `FileOutputStream`, `FilterOutputStream`, `ObjectOutputStream`, `PipedOutputStream`

public abstract class OutputStream extends Object implements Closeable, Flushable
This abstract class is the superclass of all classes representing an output stream of bytes. An output stream accepts output bytes and sends them to some sink.

Applications that need to define a subclass of `OutputStream` must always provide at least a method that writes one byte of output.

Since:
  1.0
See Also:
  - `BufferedOutputStream`
  - `ByteArrayOutputStream`
  - `DataOutputStream`
  - `FilterOutputStream`
  - `InputStream`
  - `write(int)`

- ## Constructor Summary

  Constructors
  Constructor
  Description
  `OutputStream()`
  Constructor for subclasses to call.

- ## Method Summary

  Modifier and Type
  Method
  Description
  `void`
  `close()`
  Closes this output stream and releases any system resources associated with this stream.
  `void`
  `flush()`
  Flushes this output stream and forces any buffered output bytes to be written out.
  `static OutputStream`
  `nullOutputStream()`
  Returns a new `OutputStream` which discards all bytes.
  `void`
  `write(byte[] b)`
  Writes `b.length` bytes from the specified byte array to this output stream.
  `void`
  `write(byte[] b, int off, int len)`
  Writes `len` bytes from the specified byte array starting at offset `off` to this output stream.
  `abstract void`
  `write(int b)`
  Writes the specified byte to this output stream.

  ### Methods declared in class java.lang.Object

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

- ## Constructor Details

  - ### OutputStream

    public OutputStream()
    Constructor for subclasses to call.

- ## Method Details

  - ### nullOutputStream

    public static OutputStream nullOutputStream()
    Returns a new `OutputStream` which discards all bytes. The returned stream is initially open. The stream is closed by calling the `close()` method. Subsequent calls to `close()` have no effect.

    While the stream is open, the `write(int)`, `write(byte[])`, and `write(byte[], int, int)` methods do nothing. After the stream has been closed, these methods all throw `IOException`.

    The `flush()` method does nothing.

    Returns:
      an `OutputStream` which discards all bytes
    Since:
      11

  - ### write

    public abstract void write(int b) throws IOException
    Writes the specified byte to this output stream. The general contract for `write` is that one byte is written to the output stream. The byte to be written is the eight low-order bits of the argument `b`. The 24 high-order bits of `b` are ignored.
    Parameters:
      `b` - the `byte`.
    Throws:
      `IOException` - if an I/O error occurs. In particular, an `IOException` may be thrown if the output stream has been closed.

  - ### write

    public void write(byte[] b) throws IOException
    Writes `b.length` bytes from the specified byte array to this output stream. The general contract for `write(b)` is that it should have exactly the same effect as the call `write(b, 0, b.length)`.
    Parameters:
      `b` - the data.
    Throws:
      `IOException` - if an I/O error occurs.
    See Also:
      - `write(byte[], int, int)`

  - ### write

    public void write(byte[] b, int off, int len) throws IOException
    Writes `len` bytes from the specified byte array starting at offset `off` to this output stream. The general contract for `write(b, off, len)` is that some of the bytes in the array `b` are written to the output stream in order; element `b[off]` is the first byte written and `b[off+len-1]` is the last byte written by this operation.

    If `b` is `null`, a `NullPointerException` is thrown.

    If `off` is negative, or `len` is negative, or `off+len` is greater than the length of the array `b`, then an `IndexOutOfBoundsException` is thrown.

    API Note:
      Subclasses are encouraged to override this method and provide a more efficient implementation.
    Implementation Requirements:
      The `write` method of `OutputStream` calls the write method of one argument on each of the bytes to be written out.
    Parameters:
      `b` - the data.
      `off` - the start offset in the data.
      `len` - the number of bytes to write.
    Throws:
      `IOException` - if an I/O error occurs. In particular, an `IOException` is thrown if the output stream is closed.
      `IndexOutOfBoundsException` - If `off` is negative, `len` is negative, or `len` is greater than `b.length - off`

  - ### flush

    public void flush() throws IOException
    Flushes this output stream and forces any buffered output bytes to be written out. The general contract of `flush` is that calling it is an indication that, if any bytes previously written have been buffered by the implementation of the output stream, such bytes should immediately be written to their intended destination.

    If the intended destination of this stream is an abstraction provided by the underlying operating system, for example a file, then flushing the stream guarantees only that bytes previously written to the stream are passed to the operating system for writing; it does not guarantee that they are actually written to a physical device such as a disk drive.

    Specified by:
      `flush` in interface `Flushable`
    Implementation Requirements:
      The `flush` method of `OutputStream` does nothing.
    Throws:
      `IOException` - if an I/O error occurs.

  - ### close

    public void close() throws IOException
    Closes this output stream and releases any system resources associated with this stream. The general contract of `close` is that it closes the output stream. A closed stream cannot perform output operations and cannot be reopened.
    Specified by:
      `close` in interface `AutoCloseable`
    Specified by:
      `close` in interface `Closeable`
    Implementation Requirements:
      The `close` method of `OutputStream` does nothing.
    Throws:
      `IOException` - if an I/O error occurs.