java.nio (Java SE 17 & JDK 17)
Description: declaration: module: java.base, package: java.nio
Keywords: java.nio package

Module java.base

# Package java.nio

package java.nio
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.

Description of the various buffers
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` | Get/put, compact; allocate, wrap
`FloatBuffer` | Get/put, compact; allocate, wrap
`IntBuffer` | Get/put, compact; allocate, wrap
`LongBuffer` | Get/put, compact; allocate, wrap
`ShortBuffer` | Get/put, compact; allocate, wrap
`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

- Related Packages
  Package
  Description
  java.nio.channels
  Defines channels, which represent connections to entities that are capable of performing I/O operations, such as files and sockets; defines selectors, for multiplexed, non-blocking I/O operations.
  java.nio.charset
  Defines charsets, decoders, and encoders, for translating between bytes and Unicode characters.
  java.nio.file
  Defines interfaces and classes for the Java virtual machine to access files, file attributes, and file systems.
- Class
  Description
  Buffer
  A container for data of a specific primitive type.
  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.
  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.
  InvalidMarkException
  Unchecked exception thrown when an attempt is made to reset a buffer when its mark is not defined.
  LongBuffer
  A long buffer.
  MappedByteBuffer
  A direct byte buffer whose content is a memory-mapped region of a file.
  ReadOnlyBufferException
  Unchecked exception thrown when a content-mutation method such as `put` or `compact` is invoked upon a read-only buffer.
  ShortBuffer
  A short buffer.