IO: Streams and readers

• The java.io package provides a rich framework and class library for reading and writing any type of data (text, numbers, images) in streams from any type of location (disk, network, memory).
• The package provides 2 class hierarchies: one for byte streams, the other for character streams.
• Base classes for reading data: InputStream for byte streams, Reader for character streams.
• Base classes for writing data: OutputStream for byte streams, Writer for character streams.
• Example of copying one file to another.

    Reader in = new FileReader("one.txt");
    Writer out = new FileWriter("two.txt");
    int token = -1;
     
    while( (token != in.read()) != -1 )
    {
      out.write(token);
    }
    out.close();
  

• The library uses the decorator pattern to add flexible stream handling. By chaining constructors of various classes, you can change how streams are read or written. Examples:
  1. We need to read some data on disk, and for performance reasons the read operation should be buffered.
     

       Reader bufferedFileIn = 
           new BufferedReader(new FileReader("datafile"));
     

  2. Read an in-memory byte array as UTF-8 encoded characters.
     

       byte[] data = ...;
       Reader charReader = 
           new BufferedReader(
             new InputStreamReader(
               new ByteArrayInputStream(data), "UTF-8"));