Organization

The java.io package contains dozens of classes to manage input and output using data streams, serialization, and the file system. Understanding the organization and naming strategy of the classes in the package will help you minimize the otherwise overwhelming nature of doing IO in Java.

Java IO is based upon the use of streams. A stream is a sequence of data that you can write to or read from. A stream may have a source, such as the console, or a destination, such as the file system. A stream with a source is an input stream; a stream with a destination is an output stream.

Java further distinguishes its streams by the format of the data they carry. Java contains character streams and byte streams. You use character streams to work with 2-byte (16-bit) Unicode character data. Java classes with Reader (input) and Writer (output) in their names are character streams. You use character streams to work with human-readable text.

Byte streams work with 8-bit binary data. Byte stream classes have the word Input or Ouput in their name. You normally use byte streams for working with nontext data such as image files or compiled byte codes.

Low-level Java streams support basic concepts such as reading or writing single bytes at a time. Were you able to work only with low-level streams, you would be forced to write tedious, repetitive code. Java supplies a number of higher-level streams that simplify your work by providing aggregate and additional functionality. These higher level streams are known as wrapper streams.

A wrapper stream object contains a reference to, or wraps, a low-level stream object. You interact with the wrapper stream. It in turn interacts with the wrapped low-level stream that does the dirty work.

Take a look at the java.io package, which contains a set of interfaces and classes to define the basic building blocks for IO. You will note that it is crowdedJava's IO facilities are complete but complex. The package includes specific stream implementations, including filtered, buffered, piped, and object streams.

In addition to the stream classes, the java.io package provides a set of classes to manipulate the underlying file system.