CSci 2101 Lab 1. Java variables, data types.

Due Tuesday, September 6th, at 11am (by e-mail)

25 points

The lab must be done individually.

Setup

• Log in to one of the lab machines. If you don't remember your password, I will help you reset it.
• Start a terminal window (Applications -> System Tools -> terminal)
• If you just got a new account, reset your password to something you can remember: type passwd on the command line in a terminal window. You will be asked to type your current password and then the new password twice. Note that as you are typing your password, nothing shows up on the screen (as a security measure).
• Create a subfolder in your home directory for this course files (for instance, csci2101) and a subfolder for the lab (lab1). Open a new file using jEdit, copy the program text into it from FirstJava.java, and save it under the same name (don't forget the .java extension) in the folder that you just created.
• In the terminal window type cd followed by the path to the file. Use Tab key for auto-complete.
• Compile your file: javac FirstJava.java. If there are no errors, run it: java FirstJava.

Lab questions

When you are answering these questions, feel free to delete some of the program code or comment out unnecessary print statements. All your newly added code should be in main. Don't forget to recompile your program after every change.

1. Write a comment at the top of the file with your name and the lab number. Always do this for all work that you do in this class.
2. Add a statement to multiply two integer variables (i.e. two variables of type int), print out the result.
3. Add a statement to divide two ints, store the result in a variable, and print that variable. What happens when the two numbers cannot be evenly divided? Write a comment in your program to explain the results.
4. Print out the value of n. Then write

   n = n + 3;
   

   Print out its value again. Briefly explain (in comments) what happens.
5. Change the comparison x < 5 to x <= 5, verify that it works as expected.
6. What happens if you compare characters 'a' and 'b' using <?
7. The maximum positive value that one can store in an int variable is 2147483647. What happens if you attempt to store a larger number?
8. Declare a new variable of any primitive type (give it any name you want that's not in the program already), initialize it, then print its value. Add a statement to change its value, print it out again. Feel free to use types long, short, etc if you prefer.
9. An operation % computes the remainder (also known as the residue) of integer division; it is defined on ints. Add a few statements to the program to check how it works. Does it correspond to the mathematical definition of a remainder on integer numbers? Write down your observations.
10. At the end of the program add the statements that call the method charAt on the string name:

    
    System.out.println(name.charAt(1));
    System.out.println(name.charAt(2));
    

    Explain what gets printed. Change the numbers passed to charAt if you would like to study the method more. Add another statement to print the very first character of the string.
11. The method length() (with no parameters) returns the length of the string. Call it on the string name to print out the string's length.
12. Make two deliberate errors in the program that cause it to fail compilation. What changes did you make? What were the error messages? Were they understandable? Comment out the errors.
13. Come up with two "what if" questions (for instance: what if I assign a double to a float? What if I declare two variables with the same name?). Write down your questions, your tests, and your answers.

How to submit

Send the FirstJava.java file with all your comments by email to me: elenam at morris.umn.edu. The subject of the message must be 2101 Lab 1.

CSci 2101 course web site.