Computer Science 161

Fall 2008

Laboratory exercise #2

October 30, 2008

A laboratory exercise in simple interaction with the user.  I will say some words at the start of the session, and then spend my time wandering around to give help where asked.

What you'll need:

• Either a copy of your Inventory exercise or a simple inventory / part class available as Inventory01 in the handouts folder on Hedwig
• Class Scanner01 on Hedwig
• Class JOptionPane01 on Hedwig

Copy these into your workspace before we begin.

The Scanner class:

The Scanner class gives us a basic way to communicate with the user through the terminal window.  It is a method which calls us back to the early days of interactive computing (1970's) when users interacted with a running program through a video terminal or typewriter console.

Open up the Scanner01 class. What we will do in this class will be to write a constructor and a method which will ask the user for their name, and return a greeting to the user.

Some basics: 

• We need to import the package for Scanner.  This will be java.util.Scanner
• We will need  two instance variables:  name (a String) and reader (a Scanner)

 In the constructor for this class, set reader to be a new Scanner.  The Scanner class has a number of constructors (we may use this later to read input from a file, for example).  For now, we want the input to come in from System.in (the terminal window), so we write

• Scanner reader = new Scanner(System.in);

Write a void method called hello which does the following

• Print a message asking the user for their name (use System.out.print instead of System.out.println so that the user will enter a name on the same line).
• Scanners have a method called nextLine() which returns (as a String) consisting of all the characters typed in by the user until the user hits the RETURN key.  For example,  name = reader.nextLine();
• We do not want  other characters in the string returned.  We can trim out these characters by apply ing the trim() method from the String class as, for example, name = name.trim().  If you want, you can add in toUpperCase(), another method of String: name = name.toUpperCase();

Try this out a bit.

For further reading

• The first part of chapter 5 of our textbook describes this use of the reader class.
• Also, open up the documentation for the String class and see what other things we can do with String.  We still need to be able to convert strings to numbers:  we will look at that some other time.
• Open up the documentation on the Scanner class to get a quick overview of what other options the Scanner class provides.
• The class ScannerExample on Hedwig in the handouts folder has a completed version of the class described above.

If you do this during the lab session, I will be able to help with any difficulties.

Exercise

(Due Tuesday, November 4):  Write a new public void method for your Inventory class called removePart which takes as input the index of a part in your inventory ArrayList.  Check to see that the index is in range (>= 0, < inventory.size()).  Retrieve the name of the part and use it in a message to the user asking if the user to confirm that that part is to be deleted.  If the first character of the user's response is a 'Y' or a 'y' delete the record (inventory.remove(index)) otherwise do nothing.  In either case, write a brief message saying that the part has or has not been deleted.  For this exercise, turn in a listing of the Inventory class with the added method.

Many thanks!