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

JSR 239 defines an NIO buffer building block comprising portions of the `Buffer`, `ByteBuffer`, `ShortBuffer`, `IntBuffer`, and `FloatBuffer` classes as well as the support classes `BufferUnderflowException`, `BufferUnderflowException`, and the interface `java.lang.Comparable`.

JSR 239 provides only basic buffer functionality, and does not address mapped buffers, charsets, channels, or selectors. The intent of including this NIO buffer building block is to store data to be passed to the native OpenGL ES engine on the native heap.

Although special VM support is not assumed, VM implementors are encouraged to provide acceleration for these classes by making use of VM intrinsics or similar techniques.

Disposal of indirect buffers is handled in the normal way by the garbage collector. However, direct buffers involve allocation of memory on the native heap, which is outside the scope of the garbage collector. This memory may still be in use by native code even though the buffer is no longer referenced by application code. In this case, the garbage collector will collect the Java object representing the buffer, but the buffer contents will continue to occupy memory in the native heap. The implementation must ensure that this memory is properly deallocated when it is no longer referenced by native code. The implementation may create a cleanup thread for this purpose.

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 {@link java.nio.charset} package, and the channel and selector APIs are defined in the {@link 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
> --- | ---
> `{@link java.nio.Buffer}` | Position, limit, and capacity; clear, flip, rewind, and mark/reset
> `{@link java.nio.ByteBuffer}` | Get/put, compact, views; allocate, wrap
> `{@link java.nio.MappedByteBuffer}` | A byte buffer mapped to a file
> `{@link java.nio.CharBuffer}` | Get/put, compact; allocate, wrap
> `{@link java.nio.DoubleBuffer}` | ' '
> `{@link java.nio.FloatBuffer}` | ' '
> `{@link java.nio.IntBuffer}` | ' '
> `{@link java.nio.LongBuffer}` | ' '
> `{@link java.nio.ShortBuffer}` | ' '
> `{@link java.nio.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 {@link java.nio.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 {@link java.nio.channels.FileChannel#map mapping`} a region of a file directly into memory, in which case a few additional file-related operations defined in the {@link java.nio.MappedByteBuffer} class are available.`

- A byte buffer provides access to its content as either a heterogenous 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 {@link java.lang.NullPointerException NullPointerException} to be thrown. @since 1.4 @version 1.13, 02/10/11