Java - IO - Character Stream

About

Character streams are build above byte stream. They decodes bytes into characters (or the other way around) using a specified charset.

The Java platform stores character values using Unicode conventions. Character stream I/O automatically translates this internal format to and from the local character set (which facilitates internationalization)

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Superclass

All characters stream classes are descended from

Reader (to read characters). All implementations extends the Reader abstract class.
Writer (to write characters). All implementations extends the Writer abstract class.

The Reader and Writer types handle the conversion of the encoded characters to and from bytes.

Implementation

Character streams are often “wrappers” for byte streams. Character streams:

use the byte stream to perform the physical I/O,
and handle translation between characters and bytes.

Streams Type

Base

Most of the below streams are based on this two base streams.

Base Stream	Operations	Logical unit	Description
FileReader	Byte Read	Bytes	FileReader reads bytes from an FileInputStream and decodes them as UTF-8 multi-byte characters. See byte stream
FileWriter	Byte Write	Bytes	Same as FileRead but with FileOutputStream. See byte stream

Each read or write request is handled directly by the underlying OS.

FileReader and FileWriter use an int variable to read to and write from.

inputStream = new FileReader(Parameters.FILE_PATH_READ);
int c = in.read();

It holds a character value in its last 16 bits (in the case of byte stream, it holds a byte in its last 8 bytes).

To handle byte IO,

FileReader, uses FileInputStream
FileWriter uses FileOutputStream.

Buffer

The buffer streams add a buffer functionality in order to reduce the I/O requests:

directly for CharArrayReader or CharArrayWriter
or by wrapping a Reader for BufferedReader and BufferedWriter

Base Stream	Operations	Operation unit	Description
CharArrayReader	Char Array Read	Char, Array	This class implements a character buffer that can be used as a character-input stream.
CharArrayWriter	Char Array Write	Char, Array	This class implements a character buffer that can be used as an Writer.
BufferedReader	Wrap with a buffer Byte Stream	Char, Array, Line	Reads text normally from a Reader (normally from a FileReader) stream, buffering characters.
BufferedWriter	Wrap with a buffer Byte Stream	Char, Char Array, LineSeparator	Writes text to a character-output stream, buffering characters.

BufferedReader inputStream = new BufferedReader(new FileReader("File/Path");
BufferedWriter outputStream = new BufferedWriter(new FileWriter("File/Path"));

Line and String

Wrapper Stream	Operations	Description
PrintStream	Write by printing (ln, f)	A PrintStream adds functionality to print data conveniently (Println, printf, format). PrintStream is technically a byte stream but it utilizes an internal character stream object to emulate many of the features of character streams.
PrintWriter	Write by printing (ln, f)	Prints formatted representations of objects to a text-output stream.
LineNumberReader	Read Line	A buffered character-input stream that keeps track of line numbers. A BufferedReader can also read line
StringReader	Read String	A character stream whose source is a string.
StringWriter	Write String	A character stream that collects its output in a string buffer, which can then be used to construct a string.

Example:

PrintWriter outputStream = new PrintWriter(new FileWriter(Parameters.FILE_PATH_WRITE));
outputStream.println("Add a line");

Pipe (Stream Connection)

Wrapper Stream	Operations	Description
PipedReader	Pipe	Piped character-input streams. A piped input stream should be connected to a piped output stream.
PipedWriter	Pipe	Piped character-output streams.

Tokenizer / Scanner (With Push Back)

Wrapper Stream	Operations	Description
StreamTokenizer	Tokenize	The StreamTokenizer class takes an input stream and parses it into “tokens”, allowing the tokens to be read one at a time.
PushbackInputStream	Push Back	A PushbackInputStream adds functionality to another input stream, namely the ability to “push back” or “unread” one byte.
PushbackReader	Push Back	A character-stream reader that allows characters to be pushed back into the stream.

Bridge to Byte and From Byte Stream

Wrapper Stream	Operations	Description
OutputStreamWriter	Bridge with Byte Stream	An OutputStreamWriter is a bridge from character streams to byte streams: Characters written to it are encoded into bytes using a specified charset.
InputStreamReader	Bridge with Byte Stream	An InputStreamReader is a bridge from byte streams to character streams: It reads bytes and decodes them into characters using a specified charset.