Java NIO

Chapter 2. Buffers

It’s all relative.

—Big Al Einstein

We begin our sightseeing tour of the java.nio packages with the Buffer classes. These classes are the foundation upon which java.nio is built. In this chapter, we’ll take a close look at buffers, discover the various types, and learn how to use them. We’ll then see how the java.nio buffers relate to the channel classes of java.nio.channels.

A Buffer object is a container for a fixed amount of data. It acts as a holding tank, or staging area, where data can be stored and later retrieved. Buffers are filled and drained, as we discussed in Chapter 1. There is one buffer class for each of the nonboolean primitive data types. Although buffers act upon the primitive data types they store, buffers have a strong bias toward bytes. Nonbyte buffers can perform translation to and from bytes behind the scenes, depending on how the buffer was created.^[1] We’ll examine the implications of data storage within buffers later in this chapter.

Buffers work hand in glove with channels. Channels are portals through which I/O transfers take place, and buffers are the sources or targets of those data transfers. For outgoing transfers, data you want to send is placed in a buffer, which is passed to a channel. For inbound transfers, a channel deposits data in a buffer you provide. This hand-off of buffers between cooperating objects (usually objects you write and one or more Channel objects) is key to efficient data handling. Channels will be covered ...