CSCI 151 - Lab 3
Reverse Polish Notation Calculator

Overview

In this lab, we will write two implementations of a stack and a RPN Calculator and test them with JUnit.

Materials

Setup

  1. Download the skeleton for this project.
  2. Unpack the code into a new Eclipse Java project.

Description

An expression such as 2 + 3 * 5 is ambiguous by itself, only looking at syntax. To resolve it properly we need to use the order of operations: Multiplication, then Division, then Addition, then Subtraction, or use parenthesis to force our order. (2 + 3) * 5 is different than 2 + (3 * 5).

Alternately, we can use Reverse Polish Notation to embed the precedence in the expression. By placing the operator at the end instead of in the middle of the two operands, we know exactly what operation to perform when. Our ambiguity disappears, since the above expression will need to be written as 2 3 5 * + or 2 3 + 5 * depending on the desired result.

This model of mathematical operators can be implemented with a stack. When the calculator sees an integer, it should be added to the stack. When it sees an operator (*, +, /, -, %), it should pop the two most recent elements from the stack, perform the operation, and then push the result back on the stack.

When the order of the operation matters, such as a - b, then your code should use the first element popped as b and the second element popped as a.

StackViewer

To help us visualize our implementations, you will find the StackViewer class in the numstack package, written using JavaFX. Run this program to see a text box for entry and a listing below of the current contents of the stack.

Currently, the StackViewer does not work, because it is missing a stack implementation. You must implement two versions of a stack, one using an array, and the second using a list of nodes.

Step 1 - ArrayIntStack

In the numstack.model package, you will find the following classes:

IntStack.java

This is a general interface for a stack of integers. You will want to call the default method emptyCheck() at the right places, to ensure the appropriate methods fail when necessary.

ArrayIntStack.java

You will use an array of integers to implement a stack.

Note: If you use ArrayList you will receive no credit for the assignment.

IntStackTest.java

These are the unit tests for your stack. Your grade depends on passing these tests.

ArrayIntStackTest.java

Run this file to see the results of the unit tests for your ArrayIntStack implementation.

Step 2 - ListIntStack

You will use a linked list of Nodes to implement a stack.

ListIntNode

You will first need to create a file called ListIntNode.java that implements the Node class we discussed. It should have an int item, and a ListIntNode next reference as components.

ListIntStack.java

You will use a sequence of ListIntNode objects to implement a stack.

ListIntStackTest.java

Run this file to see the results of the unit tests for your ListIntStack implementation.

Step 3 - RPNCalc

In the rpn.model package, you will find the following classes:

RPNCalc.java

This is the main file you will have to complete. You will need to make a constructor and three methods.

addTerm(String term)

This method brings in a single token as a String. If it is a number, then it should be added to the stack. If it is a valid operator, then it should perform the operation, using the top two elements of the stack, and push the result onto the stack. Otherwise, it should throw an IllegalArgumentException.

getLastValue()

This method should return the most recent integer term added to the calculator. By the end of this method, the calculator should be in EXACTLY THE SAME STATE as when the method started.

getNextToLastValue()

This method should return the second most recent integer term added to the calculator. By the end of this method, the calculator should be in EXACTLY THE SAME STATE as when the method started.

RPNCalcTest.java

These are the unit tests for your calculator. Your grade depends on passing these tests.

Op.java

This is an Enum. It is used in testing with JUnit, and you can safely ignore it.

Step 4 - TimeTest

TimeTest.java

Run this file to compare the performance of ArrayIntStack and ListIntStack.

What to Hand In

Submit your ArrayIntStack.java, ListIntStack.java, and RPNCalc.java implementations, along with any additional files you created for your implementations.

Grading

© Mark Goadrich, Hendrix College