Writing Files - Beginning Java - page 449

sequence of elements of a given type, and you can create buffers to hold any primitive data type except for
type boolean . Thus, you create different types of buffers to store byte values, char values, short values,
int values, long values, float values, or double values. The classes in Table 10-4 in the java.nio pack-
age define these buffers.
TABLE 10-4 : Classes for Buffers
CLASS DESCRIPTION
ByteBuffer A buffer that stores values of type byte . You can also store the binary values of any of the other primit-
ive types in this buffer, except for type boolean . Each binary value that you store occupies a number of
bytes in the buffer determined by the type — values of type char or short occupy 2 bytes, int values
occupy 4 bytes, and so on.
CharBuffer A buffer that stores only values of type char .
ShortBuffer A buffer that stores only values of type short .
IntBuffer A buffer that stores only values of type int .
LongBuffer A buffer that stores only values of type long .
FloatBuffer A buffer that stores only values of type float .
DoubleBuffer A buffer that stores only values of type double .
I keep repeating “except for type boolean ” every so often, so I better address that. There is no buffer type
that provides for type boolean values, but, of course, you may actually want to record some boolean values
in a file. In this case, you have to devise a suitable alternative representation. You could use integer values
0 and 1, or perhaps strings "true" and "false" , or even characters 't' and 'f' . You could even represent
each boolean value as a single bit and pack eight of them at a time into a single byte, but this is likely to be
worthwhile only if you have a lot of them. Which approach you choose depends on what is most convenient
in the context in which you are using the boolean values.
Although you have seven different classes defining buffers, you use only buffers of type ByteBuffer to
read or write data. The other types of buffers in the table above are called view buffers , because they are
usually created as views of an existing buffer of type ByteBuffer . The view buffers provide an easy way to
get data items of various types into or out of a ByteBuffer . You see how a little later in this chapter.
Buffer Capacity
The capacity of a buffer is the maximum number of values it can contain, not the number of bytes — unless,
of course, it stores elements of type byte . The capacity of a buffer is fixed when you create it and cannot
be changed subsequently. You can obtain the capacity for a buffer object as a value of type int by calling
the capacity() method that it inherits from the Buffer class. Figure 10-1 shows the capacities of different
buffers when each occupies the same amount of memory.
FIGURE 10-1