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Java Readers and Writers  «Prev  Next»
Lesson 3The Reader and Writer classes
ObjectiveExamine the Reader and Writer classes for converting character-based data.
The java.io.Reader and java.io.Writer classes are abstract superclasses for classes that read and write character-based data.
The subclasses are notable for handling the conversion between different character sets.
Input and output streams are fundamentally byte-based. However, readers and writers are based on characters. In Java, a char is a two-byte Unicode character; but in other character sets that you may have to read or write, characters can have varying widths. ASCII and ISO Latin-1 use one-byte characters. Unicode uses two-byte characters. UTF-8 uses characters of varying width between one and three bytes. Readers and writers know how to handle all these character sets and many more seamlessly.
The encoding and decoding classes themselves are hidden in the sun packages. They are used internally by the InputStreamReader and OutputStreamWriter classes to convert the bytes used by the streams into chars used by the readers and writers and vice versa.
You can also convert byte arrays in a particular character set into Unicode strings using two String constructors.
The exact list of encodings available varies a little from platform to platform. Here are most of the important ones. This same set of encodings is used by readers that convert all bytes they read into Unicode chars.

Reader Writer Classes
Every platform has a default character set that's used when no other is explicitly specified. On Windows that's likely to be ISO Latin-1. On the Mac it's likely to be MacRoman.