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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  Buffers Description  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   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.  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.
 
 
   
BufferPosition, limit, and capacity;
            
clear, flip, rewind, and mark/reset   
       ByteBufferGet/put, compact, views; allocate, wrap      
       MappedByteBuffer  A byte buffer mapped to a file    
       CharBufferGet/put, compact; allocate, wrap    
       DoubleBuffer    ' '    
       FloatBuffer    ' '    
       IntBuffer    ' '    
       LongBuffer    ' '    
       ShortBuffer    ' ' ByteOrderTypesafe enumeration for byte orders 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.
 
   
a region of a
   file directly into memory, in which case a few additional file-related
   operations defined in theMappedByteBuffer 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.
  
  
  
    
| 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. | 
| 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. |