CCSU  Fall 1998

Project 3

Posting Date: October 26, 1998
Due Date:     November 11, 1998

Relevant Demos: None.  Instead, see infix.java on pages 138 ff. of the text.

This project comes in only one part.  It covers material on stacks and 
translation from infix to postfix notation.

Background:

  The purpose of this project is to give you practice with stacks, and practice 
with an important application of stacks, translation from infix to postfix 
notation.  This, translation from infix to postfix, is closely related to 
parsing, which is the first step in compiler design.  However, it is simple 
enough so second semester students can master it.

Description:

  Write a java Applet to convert Boolean expressions from infix to postfix.  
Use & for AND, use | for OR, and use ! for NOT.  The priority of operations is

    ! has priority over & and |
    & has priority over |
    | has lowest priority

  There will be two Boolean constants, 0 for false and 1 for true.

  Use single upper case letters for variables.  For simplicity, there will be 
no spaces in valid expressions, and all variable names will be exactly one 
letter long.

  Examples:

     infix	postfix
     !A&B	A!B&
     !(A&B)	AB&!
     A&B|C	AB&C|
     A&(B|C)	ABC|&
     A&1	A1&
     A|0	A0|

  You will want to adapt the algorithm presented in table 4.10, page 131, of 
the text, and the corresponding java code given in the infix.java program on 
page 133.

  Your Applet panel will contain two Labels, two TextFields, and one Button.  
It will look something like this:

       ------------------------------------
      |                                    |
      |           --------------------     |
      |   Infix  |                    |    |
      |           --------------------     |
      |                                    |
      |             --------------------   |
      |   Postfix  |                    |  |
      |             --------------------   |
      |                                    |
      |    ---------                       |
      |   | Convert |                      |
      |    ---------                       |
      |                                    |
       ------------------------------------

  The user should be able to type a valid Boolean infix expression into the 
Infix TextField, click the Convert Button, and see the corresponding postfix 
expression appear in the Postfix TextField.  If the user types in an invalid 
expression and clicks the Convert Button, a message such as "Invalid Boolean 
Expression should appear in the Postfix box.

   The text describes how to find most errors -- something ends up left on the 
stack when you finish converting.  You may need to add a symbol checker method 
to check that the current symbol is a valid one.  Valid symbols are upper case 
letters, the digits 0 and 1, the operators &, | and !, and left and right 
parentheses.

  If you wish, you may add a Label or two saying things like "Infix to Postfix 
Converter" and "for Boolean Expressions".

  Students who need help with Applets will find copious examples in the demos 
on the Spring 1998 CS 151 Web page, accessible from the Web page for this 
course via the Java Resources page.

General Instructions:

(1) Hand in a FOLDER containing (1) a printed copy of the text of the RPN.java 
Applet, and (2) a 3.5" floppy disk with the .java and .class files for your 
class.  The folder should have a pocket, as described in project 1.

(2) Your .java and .class files MUST be named and RPN.java, RPN.class. There 
are no data and output files.

(3) Your program must begin with a remark box, as described in project 1.  
Under files, list none.

(4) Each method in your program must begin with a remark box as described in 
project 1.

(5) Your program MAY NOT use a depreciated api, as described in project 1.