Input and output, I/O for short, are fundamental to any computer operating system or programming language. Only theorists find it interesting to write programs that don't require input or produce output. At the same time, I/O hardly qualifies as one of the more "thrilling" topics in computer science. It's something in the background, something you use every daybut for most developers, it's not a topic with much sex appeal.
But in fact, there are plenty of reasons Java programmers should find I/O interesting. Java includes a particularly rich set of I/O classes in the core API, mostly in the java.io and java.nio packages. These packages support several different styles of I/O. One distinction is between byte-oriented I/O, which is handled by input and output streams, and character-I/O, which is handled by readers and writers. Another distinction is between the old-style stream-based I/O and the new-style channel- and buffer-based I/O. These all have their place and are appropriate for different needs and use cases. None of them should be ignored.
Java's I/O libraries are designed in an abstract way that enables you to read from external data sources and write to external targets, regardless of the kind of thing you're writing to or reading from. You use the same methods to read from a file that you do to read from the console or from a network connection. You use the same methods to write to a file that you do to write to a byte array or a serial port device.
Reading and writing without caring where your data is coming from or where it's going is a very powerful abstraction. Among other things, this enables you to define I/O streams that automatically compress, encrypt, and filter from one data format to another. Once you have these tools, programs can send encrypted data or write zip files with almost no knowledge of what they're doing. Cryptography or compression can be isolated in a few lines of code that say, "Oh yes, make this a compressed, encrypted output stream."
In this book, I'll take a thorough look at all parts of Java's I/O facilities. This includes all the different kinds of streams you can use and the channels and buffers that offer high-performance, high-throughput, nonblocking operations on servers. We're also going to investigate Java's support for Unicode. We'll look at Java's powerful facilities for formatting I/O. Finally, we'll look at the various APIs Java provides for low-level I/O through various devices including serial ports, parallel ports, USB, Bluetooth, and other hardware you'll find in devices that don't necessarily look like a traditional desktop computer or server.
I won't go so far as to say, "If you've always found I/O boring, this is the book for you!" I will say that if you do find I/O uninteresting, you probably don't know as much about it as you should. I/O is the means for communication between software and the outside world. Java provides a powerful and flexible set of tools for doing this crucial part of the job. Having said that, let's start with the basics.
Streams in Memory
The File System
Working with Files
File Dialogs and Choosers
Character Sets and Unicode
Readers and Writers
Formatted I/O with java.text
The Java Communications API
The J2ME Generic Connection Framework