Streams - Java Network Programming - page 45

In this mirror image hierarchy, two abstract superclasses define the basic API for reading
and writing characters. The java.io.Reader class specifies the API by which characters
are read. The java.io.Writer class specifies the API by which characters are written.
Wherever input and output streams use bytes, readers and writers use Unicode char‐
acters. Concrete subclasses of Reader and Writer allow particular sources to be read
and targets to be written. Filter readers and writers can be attached to other readers and
writers to provide additional services or interfaces.
The most important concrete subclasses of Reader and Writer are the InputStream
Reader and the OutputStreamWriter classes. An InputStreamReader contains an un‐
derlying input stream from which it reads raw bytes. It translates these bytes into Uni‐
code characters according to a specified encoding. An OutputStreamWriter receives
Unicode characters from a running program. It then translates those characters into
bytes using a specified encoding and writes the bytes onto an underlying output stream.
In addition to these two classes, the java.io package provides several raw reader and
writer classes that read characters without directly requiring an underlying input
stream, including:
• FileReader
• FileWriter
• StringReader
• StringWriter
• CharArrayReader
• CharArrayWriter
The first two classes in this list work with files and the last four work inside Java, so they
aren't of great use for network programming. However, aside from different construc‐
tors, these classes have pretty much the same public interface as all other reader and
writer classes.
Writers
The Writer class mirrors the java.io.OutputStream class. It's abstract and has two
protected constructors. Like OutputStream , the Writer class is never used directly; in‐
stead, it is used polymorphically, through one of its subclasses. It has five write()
methods as well as a flush() and a close() method:
protected Writer ()
protected Writer ( Object lock )
public abstract void write ( char [] text , int offset , int length )
throws IOException
public void write ( int c ) throws IOException