The Java Way of File Operations

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The Java Way of File Operations Interfaces and classes for dealing with files and other I/O types are in the java.io package. An interface is a class that contains abstract methods. Classes in java.io form a class hierarchy. The two main class types in java.io are text oriented (character streams) and binary oriented (byte streams). Subclasses of the Reader and Writer classes are text oriented; those of the InputStream and OutputStream classes are binary oriented. InputStream and OutputStream are abstract; that is, they can't be instantiated directly. To use an abstract class you must subclass it and instantiate the subclass. The subclasses of InputStream and OutputStream allow the reading of binary data to and from various types of input and output such as byte arrays (memory), files, and even network sockets. Streams can be chained to provide extra functionality. For example, you can buffer a FileInputStream by chaining it to a BufferedInputStream Then you can chain the BufferedInputStream to an ObjectInputStream to read in whole objects at one time. (This is similar to the pickle functionality in Python.) Java 1.1's binary data input streams are complemented by somewhat equivalent text input streams. The parents of these classes are the abstract classes Reader and Writer. Having an equivalent set of text-oriented character stream classes allows the conversion of Unicode text. Readers and Writers, like streams, can be chained together. For example, you can buffer a FileReader by chaining it to a BufferedReader. (Buffering will be explained shortly.) I/O Classes to Be Covered There are more than thirty I/O classes, not including interfaces and abstract classes. This seems like a lot, but if you understand how Reader, Writer, InputStream, and OutputStream work, you can easily understand the rest. Reader and Writer subclasses deal with character streams, that is, text. InputStream and OutputStream subclasses deal with binary streams. An easy way to remember this is, if you can read it, use Reader and Writer; if you can't, use InputStream and OutputStream. For Beginners: Understanding Streams Think of a stream as an abstract file. Just as you can read and write to a file, you can read and write to a stream. You might use a stream for reading and writing with an RS-232 serial connection, a TCP/IP connection, or a memory location (like a sequence). A stream is abstract, so if you know how to read and write to a file, you basically already know how to read and write to a memory location or an RS-232 serial connection or, for that matter, a Web site. This is the art and magic of polymorphism.

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