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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
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