OutputStream (Java Platform SE 8 )
Keywords: java.io.OutputStream class
Date: 2026-08-19

compact1, compact2, compact3
java.io

## Class OutputStream

- java.lang.Object
- - java.io.OutputStream

- All Implemented Interfaces:
    Closeable, Flushable, AutoCloseable
  Direct Known Subclasses:
    ByteArrayOutputStream, FileOutputStream, FilterOutputStream, ObjectOutputStream, OutputStream, 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:
    JDK1.0
  See Also:
    `BufferedOutputStream`, `ByteArrayOutputStream`, `DataOutputStream`, `FilterOutputStream`, `InputStream`, `write(int)`

- - ### Constructor Summary

    Constructors
    Constructor and Description
    `OutputStream()`

  - ### Method Summary

    All Methods Instance Methods Abstract Methods Concrete Methods
    Modifier and Type | Method and 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.
    `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 inherited from class java.lang.Object

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

- - ### Constructor Detail

    - #### OutputStream

          public OutputStream()

  - ### Method Detail

    - #### 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.

      Subclasses of `OutputStream` must provide an implementation for this method.

      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.

      The `write` method of `OutputStream` calls the write method of one argument on each of the bytes to be written out. Subclasses are encouraged to override this method and provide a more efficient implementation.

      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.

      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.

    - #### 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.

      The `flush` method of `OutputStream` does nothing.

      Specified by:
        `flush` in interface `Flushable`
      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.

      The `close` method of `OutputStream` does nothing.

      Specified by:
        `close` in interface `Closeable`
      Specified by:
        `close` in interface `AutoCloseable`
      Throws:
        `IOException` - if an I/O error occurs.

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