Lab 3 -- Input/Output (I/O) Unit

Related Reading

3.1 Streams

The I/O unit communicates with the outside world using streams. Intuitively streams are unbounded sequences of values. The java.io package supports streams extensively.

Underlying any Java stream is a stream of bytes. Such byte streams called InputStream and OutputStream are low-level and rarely used directly in applications. For our purposes, we would like to view the input stream as carrying a sequence of numbers and we would also like to write arbitrary values to the output stream. We can achieve this with a bit of work.

First, we move from byte streams to character streams using the classes InputStreamReader and OutputStreamWriter. The read and write operations on these streams handle only one character at a time (which may correspond to more than one byte on the underlying byte stream). For efficiency, these streams are usually wrapped using a BufferedReader and BufferedWriter.

Next, we can automatically convert a stream of characters to a stream of "tokens" where tokens represent entities such as strings, numbers, etc. This is achieved using the rather flexible class StreamTokenizer. The behavior of this class can be parameterized by a number of flags so you will need to consult the API before using it. Symmetrically, we can write arbitrary Java objects to a character stream by first wrapping it in a PrintWriter stream.

3.2 The I/O Interface

The I/O unit of the machine has a simple interface. It communicates with the outside worlds using two streams. The methods getWriter and getReader return the high-level streams used to communicate with the outside world. The unit can readData from the input stream and printData to the output stream: 

import java.io.*;

public interface ioUnitI {
  InputStream DEFAULT_ISTREAM = System.in;
  OutputStream DEFAULT_OSTREAM = System.out;

  PrintWriter getWriter ();
  StreamTokenizer getReader ();

  Word readData () throws ioE;
  void writeData (Word w);
}

All inputs to our machine are numbers that are converted to integers and stored in the memory. A call to the method readData may throw an exception if the input cannot be parsed as a number. More importantly, the call will block waiting for input if there are no characters to read from the input stream. This is consistent with the intuitive behavior of programs: if a program is requesting an input value, then it will wait (block) until that value is supplied.

3.3 Exercise

Write the class ioUnit that implements the interface ioUnitI. You will need to read the documentation of the java.io package (especially the API for StreamTokenizer) carefully using the guidelines above.

You should provide two constructors for the I/O unit. The first should take no arguments and use the default streams. The second constructor should take an InputStream and an OutputStream as arguments.

The help files are at the URL: http://www.cs.uoregon.edu/~sabry/duckMachine/ioUnit/

and include:

Turn in the code for ioUnit.java during class on Monday, April 26th.

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Last modified: 04/13/99 13:58:25

yreimer@cs.uoregon.edu