Basic Classes for Input/Output in Java

The Source of the Data

• Traditionally data came from disk files or the keyboard.
• In some languages, these two data sources were treated identiacally, in others (usualy older languages), keyboard and disk file input were handled differently.
• In Java, we'd like to keep our options open and flexible-- keyboard data, file data, data from a web page, etc.
• There is a class called FileInputStream whose behavior is to read 8-bit 'characters' from a disk file.

The ASCII/Unicode Dichotomy

• With the advent of the global reach of the internet, it became desireable to support alphabets other than the standard Latin character set used in English.
• The introduction of Unicode and its 16-bit character induced Java to use a 16-bit character type (rather than the traditional 8-bit ASCII).
• However, most data files were still encoded in 8-bit ASCII, and thus a translation was needed.
• In Java, ASCII (i.e.. 8-bit) input is handled by a family of classes known as InputStreamss; while Unicode input is handled by the family of classes known as Readers.
• There is a class called InputStreamReader whose behavior is to translate 8-bit 'characters' into full 16-bit Unicode characters.

Buffering the Input

• The basic InputStream and Reader classes read single characters at a time.
• The class BufferedReader buffers (i.e., groups) characters together into sequences of lines. This class provides the method readLine which returns a String containing the next line of the file.

Opening and Reading a File

• Create a FileInputStream object, specfiying the file
• Create a InputStreamReader object, providing it with the FileInputStream object.
• Create a BufferedReader object, providing it with the InputStreamReader object (which is a Reader object).
• Invoke the readLine method on the BufferedReader object.

Accessing the I/O Classes

import java.io.*;