Problem Description

For this program, you will write a GUI (Graphical User Interface)-based Calculator that can evaluate simple binary expressions. The user will enter an expression of the form

operand1 operator operand2

into the text field of a dialog box (shown below), where the operands and the operator are separated by spaces. For example, to add 2 and 3, the user would enter

2 + 3

The class "GUICalculator.java" is provided for you. The program, as given, creates a dialog box that takes input from the user and stores it in the local variable "inputString". A second local variable, "outputString", which you will use for your output, contains the output that will be written to screen in a message box as shown below. Requirements on your implementation and output are described below.

Implementation

Design and create a class called "Expression" that will contain methods and possibly instance variables to aid you in processing and evaluating the input. At the very LEAST, your Expression class must divide the task of evaluating the input into the following sub-tasks, each of which must be implemented by at least one method

• Parse the input into its components (an operator and two operands)
• Check the expression for errors (described below)
• Evaluate the expression, returning the result

• You may include additional methods if desired
• You may process all operands as if they were floating-point values
• You must support the following operators: addition (+), subtraction (-), multiplication (*), and division (/)

Once you have completed your Expression class, add code to "GUICalculator.java" (where indicated by the comment //YOUR CODE & METHOD CALLS HERE) that uses your Expression class to process the input and produce the correct output.

Errors

Your code must check for the following error conditions

• In the case of division, you should check for divide by zero and print an appropriate error message instead of the normal output.
• In the case that an invalid operator is entered, print an appropriate error message instead of the normal output.

Output

In the case of valid input, your program should output the initial expression entered by the user followed by an equals sign and then the result as shown in the figure above.

In the case of invalid input, your program should output an error message that is specific to the type of error encountered, e.g. "Divide by Zero".

Submission

For this assignment you will need to create a Jar file that contains the source code for Expression.java AND GUICalculator.java that you edited as part of this assignment. Follow these instructions for creating a Jar file.
The Jar file you submit must be named yourlastname_pro4.jar, where yourlastname is your last name.

Submit yourlastname_pro4.jar via the UNC Blackboard System before the deadline.

Grading

• [2] Program Headers edited correctly
• [3] JAR file submitted and named correctly (as specified above)
• [10] Your program must parse the input string correctly
• [5] Your program must evaluate the expression correctly
• [2] Your program must produce an error message in the case of divide by zero
• [3] Your program must produce an error message in the case of an unsupported operator
• [15] Your implementation must include methods that solve the sub-tasks described above
• [5] Your code must be appropriately commented
• [5] Your code must follow stylistic conventions and be neatly formatted