inputsteam reads a byte each time, and inputstreamreader can convert byte to characher, and then reads a character each time, and reader also reads a character each time, so what is the difference between them?
3 Answers
The InputStreamReader handles the encoding. A character does not always fit into a byte(8bit) and the byte value does not always map to the same char, the java char for example uses 16bit to encode a character which makes it possible to represent a greater number of different characters.
Depending on the source of the InputStream a character may be encoded with ASCII(1 byte), UTF-8(1 or more byte), UTF-16(2 or 4 byte), utf-32(4 byte) or any other existing encoding. Given the right Charset a Reader can convert the raw bytes into the corresponding java character.
Comments
From the JavaDocs:
Input Stream: This abstract class is the superclass of all classes representing an input stream of bytes
Input Stream Reader: a bridge from byte streams to character streams: It reads bytes and decodes them into characters using a specified charset
The stream just gives you the raw bytes, the reader can convert the raw bytes into characters for different encodings (ASCII/ISO/UTF).
http://download.oracle.com/javase/6/docs/api/java/io/InputStream.html http://download.oracle.com/javase/6/docs/api/java/io/InputStreamReader.html http://download.oracle.com/javase/6/docs/api/java/nio/charset/Charset.html
1 Comment
MJB
It's worth mentioning that one should usually NEVER use things like FileReader/FileWriter etc by themselves, because they always use the default encoding, which is often what you don't want. Usually you do fs=new FileInputStream and wrap that in InputStreamReader(fs,"UTF-8") or whatever.
InputStreamReader is an implementation of the abstract class Reader that reads character from an InputStream, converting bytes according to a given charset. There are other implementations of Reader too, for example StringReader which return character from a string and does not need any charset conversion.
