Java in a Nutshell, 5th Edition

Name

ByteBuffer

Synopsis

ByteBuffer holds a sequence of bytes for use in an I/O operation. ByteBuffer is an abstract class, so you cannot instantiate one by calling a constructor. Instead, you must use allocate( ) , allocateDirect( ), or wrap( ).

allocate( ) returns a ByteBuffer with the specified capacity. The position of this new buffer is zero, and its limit is set to its capacity. allocateDirect( ) is like allocate( ) except that it attempts to allocate a buffer that the underlying operating system can use “directly.” Such direct buffers” may be substantially more efficient for low-level I/O operations than normal buffers, but may also have significantly larger allocation costs.

If you have already allocated an array of bytes, you can use the wrap( ) method to create a ByteBuffer that uses the byte array as its storage. In the one-argument version of wrap( ) you specify only the array; the buffer capacity and limit are set to the array length, and the position is set to zero. In the other form of wrap( ) you specify the array, as well as an offset and length that specify a portion of that array. The capacity of the resulting ByteBuffer is again set to the total array length, but its position is set to the specified offset, and its limit is set to the offset plus length.

Once you have obtained a ByteBuffer, you can use the various get( ) and put( ) methods to read data from it or write data into it. Several versions of these methods exist to read and write single bytes or ...