1. practice using command-line arguments in a program,
2. practice writing while and for loops, including the new enhanced for loop, and
3. modify a program to include a JButton from javax.swing to exit (if time permits). 

Part 1:

Download RevPolish.java file

1. Log in to your Vassar CS account by typing your username and password at the login window.
    
2. In the cs125 directory on your Desktop (or in a place of your own choosing), make a new directory for lab 2 by entering:

         mkdir lab2
   

3. Change to the directory you made in the last step by entering:

        cd lab2
   

4. Open a web browser.
    
5. Open the course web page by going to url  www.cs.vassar.edu/~cs125  

   Download the file  RevPolish.java  into your cs125/lab2 directory. If you use the rightmost mouse button while pointing at the RevPolish.java link, you can choose the option of saving the file.
    
   This program is intended to be the basis for a very simple "reverse Polish" calculator (so-called because the operands are entered before the operator). Reverse Polish notation (or just RPN) by analogy with the related Polish notation, a prefix notation introduced in 1920 by the Polish mathematician Jan Lukasiewicz, is a mathematical notation wherein every operator follows all of its operands. It is also known as Postfix notation and is parenthesis-free.

6. Compile the RevPolish.java file in the Console window by typing  javac RevPolish.java  at the command line (or by pressing the Compile button inside DrJava). The file should compile with no errors.
     
   Run the file by typing  java RevPolish 3 4  at the command line or in the DrJava interactions pane. The file should output the line  3 + 4 = 7  to the standard output (the screen). 
    
   
7. To edit the RevPolish.java file, open it in the editor or IDE of your choice (e.g., DrJava, NetBeans, emacs,...)  You may want to seek help from your coach or professor if using NetBeans. In its present form, the file takes two operands as command line arguments args[0] and args[1], converts the strings to integers and then adds the numbers, printing the result to the screen.
    

Create a reverse Polish calculator

Augment the  RevPolish.java  file so that it takes a third argument from the command line. This argument (args[2]) will be one of the following arithmetic operators:

             + - * / %

When finished, your program should read three arguments from the command line, determine the correct operation to perform on the two integers, perform the operation, and produce the result. An example session from running the program would appear as follows (the ">" is the prompt from either the command line or the DrJava interactions pane and the bolded text is what the user types to run the program):

      > java RevPolish 3 67 +
      
      > 3 + 67 = 70

      > java RevPolish 8  2 *

      > 8 * 2 = 4

      > java RevPolish 23  3 %

      > 23 % 3 = 2

Part 2:

1. A constructor with no arguments:
   public LoopDeeLoop()
    
   
2. A private method for each exercise listed below, exercise1...exercise4.
   
   exercise1 through exercise4 should call private helper methods.
     
3. A private method with no arguments:
   private String dashLine()
   // Constructs and returns a String composed of 50 to 80 dashes
   

1. Print all integers from 0...100 that are both evenly divisible by 3 and 5.
    
   
2. Print the first 10 powers of 2 (be sure these are printed as integers.)
    
   
3. Print the sequence of integers, beginning at 100, counting downward by 5 ([100, 95, 90,85, ...]), and ending at or above 0. 
     
4. Create an array of integers and use the enhanced for loop-to print its elements.
    
   
5. Call the  dashLine() method before and after each of exercises 1 through 4.
   

Part 3:

1. Import the packages javax.swing, java.awt.event, and acm.graphics.
   
   
2. Declare a private JButton instance variable.
      
3. Add a public void method called init that takes no parameters and contains the code to
   
   
   • instantiate the JButton object with label "Exit"
   • add the JButton to the SOUTH border of the window
   • add action listeners
    
   
4. Add an actionPerformed method with definition public void actionPerformed(ActionEvent e) that contains the single statement
    
            System.exit(0);
   
   This line causes the system to exit the window.
    

After the Lab