Outline of Class 15: Program Input

Miscellaneous

• Assignment two returned. You may also want to check the general notes on that assignment and my solution to a similar assignment.
• Note that I've given up on the "Excellent -> Poor" grading scale, and am going with more descriptive terms.
• Any questions on assignment three?
• So, what were your answers to the take-home exercise?

Program Input

• Program input in Java is somewhat more complicated than output.
• There is a System.in object for the standard input to a program, corresponding to the System.out object for standard output.
• System.in is a member of java.lang.InputStream.
• Unfortunately, you cannot directly access InputStreams.
• Why? Because there are typically a number of things that you want to do with input.
  • You may want to buffer the input (group a sequence of characters into a larger array). This generally speeds up the program and, more importantly, lets you "unread" elements
  • You may want to specify the encoding used in the input.
• In Java 1.0, you must construct a DataInputStream from the input stream.
  • This can help generalize your code, as you can quickly change a program from reading standard input to reading a file by building a DataInputStream from the file, rather than standard input.
  • DataInputStream provides much more useful and usable methods than InputStream. However, these methods are generally only appropriate for non-character data and assume that you've written the data using a DataOutputStream.
  • The safest thing to use is DataInputString.readByte(), but that will require you to do a lot of work converting to appropriate forms.
  • These methods all throw IOExceptions, so you may need to catch them.
  • There is no explicit end-of-file test. Rather, an EOFException is thrown when you try to read beyond the end of the file.
• DataInputStream and its associated exceptions are not automatically part of your program. You must import them. It is easiest to do so with import java.io.*.
• Java 1.1 introduced Reader (and, more importantly, InputStreamReader and BufferedReader).
  • To get an object from which you can read lines, you would use
    new BufferedReader(new InputStreamReader(System.in));
  • The readLine() method does not seem to throw EOFExceptions.

Bailey's ReadStream Class

• Because Java-style I/O is such a pain, the author of our textbook has provided a nice interface through the ReadStream class.
• You can find information on this class at http://www.math.grin.edu/~rebelsky/Courses/152/97F/BaileyDocs/structure.ReadStream.html.
• Basically, you construct a new member of that class, and then you can do fun things like
  • reading individual characters with readChar()
  • reading whole lines with readLine()
  • reading integers with readInt()
  • checking end of file with eof()

Exercise

• Write a program that reads a series of integers from standard input (one per line), and reports on the maximum, minimum, and average.
• If you have time, make sure that your program doesn't crash if incorrect input is given.
• If you have time and inclination, extend your program to compute the median.