The concept of file

Files are the most important mechanism for storing data permanently on mass-storage devices. Permanently means that the data is not lost when the machine is switched off. Files can contain:

• data in a format that can be interpreted by programs, but not easily by humans (binary files);
• alphanumeric characters, codified in a standard way (e.g., using ASCII or Unicode), and directly readable by a human user (text files). Text files are normally organized in a sequence of lines, each containing a sequence of characters and ending with a special character (usually the newline character). Consider, for example, a Java program stored in a file on the hard-disk. In this unit we will deal only with text files.

Each file is characterized by a name and a directory in which the file is placed (one may consider the whole path that allows one to find the file on the hard-disk as part of the name of the file).

The most important operations on files are: creation, reading from, writing to, renaming, deleting. All these operations can be performed through the operating system (or other application programs), or through suitable operations in a Java program.