java.nio (Java Platform SE 8 )
Keywords: java.nio package
Date: 2026-07-22

compact3

# Package java.nio

Defines buffers, which are containers for data, and provides an overview of the other NIO packages.

See: Description

- Class Summary
  Class | Description
  --- | ---
  Buffer | A container for data of a specific primitive type.
  ByteBuffer | A byte buffer.
  ByteOrder | A typesafe enumeration for byte orders.
  CharBuffer | A char buffer.
  DoubleBuffer | A double buffer.
  FloatBuffer | A float buffer.
  IntBuffer | An int buffer.
  LongBuffer | A long buffer.
  MappedByteBuffer | A direct byte buffer whose content is a memory-mapped region of a file.
  ShortBuffer | A short buffer.

- Exception Summary
  Exception | Description
  --- | ---
  BufferOverflowException | Unchecked exception thrown when a relative put operation reaches the target buffer's limit.
  BufferUnderflowException | Unchecked exception thrown when a relative get operation reaches the source buffer's limit.
  InvalidMarkException | Unchecked exception thrown when an attempt is made to reset a buffer when its mark is not defined.
  ReadOnlyBufferException | Unchecked exception thrown when a content-mutation method such as `put` or `compact` is invoked upon a read-only buffer.

## Package java.nio Description

Defines buffers, which are containers for data, and provides an overview of the other NIO packages.

The central abstractions of the NIO APIs are:

- Buffers, which are containers for data;

- Charsets and their associated decoders and encoders,
  which translate between bytes and Unicode characters;

- Channels of various types, which represent connections
  to entities capable of performing I/O operations; and

- Selectors and selection keys, which together with
  selectable channels define a multiplexed, non-blocking
  I/O facility.

The `java.nio` package defines the buffer classes, which are used throughout the NIO APIs. The charset API is defined in the `java.nio.charset` package, and the channel and selector APIs are defined in the `java.nio.channels` package. Each of these subpackages has its own service-provider (SPI) subpackage, the contents of which can be used to extend the platform's default implementations or to construct alternative implementations.

> Buffers | Description
> --- | ---
> ``Buffer`` | Position, limit, and capacity; clear, flip, rewind, and mark/reset
> ``ByteBuffer`` | Get/put, compact, views; allocate, wrap
> ``MappedByteBuffer`` | A byte buffer mapped to a file
> ``CharBuffer`` | Get/put, compact; allocate, wrap
> ``DoubleBuffer`` | ' '
> ``FloatBuffer`` | ' '
> ``IntBuffer`` | ' '
> ``LongBuffer`` | ' '
> ``ShortBuffer`` | ' '
> ``ByteOrder`` | Typesafe enumeration for byte orders

A buffer is a container for a fixed amount of data of a specific primitive type. In addition to its content a buffer has a position, which is the index of the next element to be read or written, and a limit, which is the index of the first element that should not be read or written. The base `Buffer` class defines these properties as well as methods for clearing, flipping, and rewinding, for marking the current position, and for resetting the position to the previous mark.

There is a buffer class for each non-boolean primitive type. Each class defines a family of get and put methods for moving data out of and in to a buffer, methods for compacting, duplicating, and slicing a buffer, and static methods for allocating a new buffer as well as for wrapping an existing array into a buffer.

Byte buffers are distinguished in that they can be used as the sources and targets of I/O operations. They also support several features not found in the other buffer classes:

- A byte buffer can be allocated as a direct buffer, in which case the Java virtual machine will make a best effort to perform native I/O operations directly upon it.

- A byte buffer can be created by `mapping` a region of a file directly into memory, in which case a few additional file-related operations defined in the `MappedByteBuffer` class are available.

- A byte buffer provides access to its content as either a heterogeneous or homogeneous sequence of binary data of any non-boolean primitive type, in either big-endian or little-endian byte order.

Unless otherwise noted, passing a `null` argument to a constructor or method in any class or interface in this package will cause a `NullPointerException` to be thrown.

Since:
  1.4

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