Introduction

This assignment tests your basic programming skill in Java and refreshes the programming skills that you should have learnt in the first programming course.

You are asked to write a postfix to infix convertor. Although program design will not be evaluated in this assignment, you are encouraged to apply the object-oriented programming technique that you have learnt.

You are also required to write JavaDoc for all non-private classes and non-private class members. Programs without JavaDoc will not be marked.

Requirements

You will be provided a skeleton file, PostfixReader.java, which consists of a simple main() method that controls the basic program flow; and a method that reads a line from input which is implemented for you. You will need to implement the doConversion() method that read an Postfix from input (using the provided readPostfix() method), convert that to infix and print it out. In addition, print the result of the input equation to the next line.

To support the postfix to infix conversion, you are required to implement the class Stack. You are not allowed to use any class provided in the packages in java.util.* or any other Java classes that provide the implementation of a stack from the Internet. Please refer to the Assignment1_Background Slides for the basic operations of a stack.

Your program should read in an arithmetic expression in postfix form, and output the same expression in infix form. Numbers and operators including parenthesis in the expression are separated by at least one single space. For example:

Input postfix: 12 23

Infix: ( 12 + 23 )

Result: 35

Input postfix: 34 56 *

Infix: ( 34 * 56 )

Result: 1904

Your program should support the five arithmetic operators, ^, +, -, * and /. The ^ is the exponential operator and has the highest precedence. The precedence of operators * and / are higher than that of operators + and -. For example:

Input postfix: 1 2 + 3 *

Infix: ( ( 1 + 2 ) * 3 )

Result: 9

Input postfix: 8 64 4 2 ^ /

Infix: ( 8 ( 64 / ( 4 ^ 2 ) ) )

Result: 4

Your program should support negative values. There is no space between the negative sign and the number in negative values. For example:

Input postfix: 5 -2 2 *

Infix: ( 5 + ( -2 * 2 ) )

Result: 1

Your program should also detect the validity of postfix expressions. For example:

Input postfix: 2 + 3 *

Error: Invalid postfix

Input postfix: 1 3 5 * + 7 /

Error: Invalid postfix

Marking

• 60% marks are given to the functionality of your program.
  • You may add additional classes, instant variables and methods to the class.
  • You may assume that the input is always a space delimited expression.
  • Your program output must be identical to what is described in this document, with the exception of the trailing spaces at the end of each line of output.
• 40% marks are given to your JavaDoc. A complete JavaDoc includes documentation of every classes, member fields and methods that are not private. JavaDoc for the main method may be omitted.