Description
Part 1: Get your environment set up
• If you are working on your own computer… Set up the Dr. Java IDE. The Google Drive contains
installation instructions.
• If you are working in one of the Benton labs… Dr. Java is already installed
• Under Dr. Java’s Edit menu, select “Preferences” and make some changes that will make Dr.
Java easier to use…
o Under the “Display Options” section, check the box next to “Show All Line Numbers”.
o Under the “Miscellaneous” section, set the “Indent Level” to 3.
o Click “OK” to apply these changes and return to the programming environment.
CSE 174 – Program 1 Page 2
Part 2: Type your source code
The next several pages contain the source code for a Java program. Using Dr. Java, type it in exactly as
shown, including indentation, comments, blank lines, upper/lowercase, etc.
Begin by typing this much (Don’t type the line numbers. They will show up automatically.):
Things to notice:
Indentation: If you do not make any mistakes in your typing, then Dr. Java will automatically indent each line as shown above.
Indentation is important because it helps humans (such as you and your peers and instructors) read your code.
Curly braces: Lines 11, 13, 17, 21, and 25 contain opening curly braces, and lines 15, 19, 23, 27, and 29 contain closing curly
braces. Curly braces are important because the Java compiler looks for them to know when a block of code begins and ends.
Comments: Beginning a line with a double slash, //, indicates that the text is a comment for humans (the compiler ignores it).
Color coding: Dr. Java will automatically color code certain words blue, comments will be green, and unrecognized words
black. This helps humans read your code.
Upper/lowercase: Note that only a few words begin with an uppercase letter (Scanner, MyFirstProgram, and String).
Java is case sensitive, meaning that the Java compiler considers Scanner, scanner, SCANNER, and ScAnNeR to be different.
(You will see later that choosing uppercase vs. lowercase helps humans as well.)
Modify this section with
your name, instructor,
section, and date.
CSE 174 – Program 1 Page 3
Get to know the basic “structure” of a Java program:
Make it easier to spot your curly braces:
One technique that programmers often use to make their code easier to read is to put a comment
after the closing brace of each class and method to indicate which code has just ended. Modify your
code to include the comments shown below:
Basic structure:
One class: Represented by all the code within
the yellow rectangle. Notice that the curly
brace at the end of line 11 marks the
beginning of that block of code, and the curly
brace at the end of line 29 ends that block of
code.
Four methods: Our class contains four
methods, highlighted in orange. The names
of these methods are: main, greet,
explainGame, and printBorder. Each
method has its own set of curly braces.
One of those methods is named main:
When you tell the Java Virtual Machine to run
a program, the JVM will look for the method
named main. Without it, you would get an
error message indicating that no main
method was found.
In CSE 174, most of the programs we write will
consist of one class with multiple methods.
CSE 174 – Program 1 Page 4
Explain the purpose of your program:
Before writing the code for a class or any of its methods, write comments to summarize the purpose of
that code:
The comments before a class should summarize the purpose of the class as a whole.
The comments before a method should summarize the purpose of that specific method.
Later, we may put comments within a method to explain what part of that method does. For now, add
the following comments to your code.
Use the Enter key!
Unlike when using a word
processor, you need to press
the “Enter” key at the end of
each line.
As a bonus: when you press
enter at the end of a line, Dr.
Java should automatically
indent your code correctly.
As a general rule we will look
for a way to keep every line of
our program at 70 characters
or fewer. Notice that Dr. Java
indicates the current line
number and column in the
lower right hand corner . For
example, this is what would
be displayed if the cursor
were on line number 34,
column 11:
For now, just match the lines
you type to what is shown to
the left.
CSE 174 – Program 1 Page 5
A key to writing programs is to save, compile, and test frequently.
Write a little, save it, compile it, and test it.
Write a little more, save it, compile it, and test it.
Write a little more, save it, compile it, and test it.
So…save your work and compile it. If you get an error message…
Read the message.
Note the line number where the error occurred (often, the actual mistake comes before that
line number).
Try to figure out how to fix the problem on your own. If you are stuck, copy the error message,
go to the discussions at the course website and paste the exact error message along with any
other pertinent information, and see if anyone has a suggestion.
Don’t move on until the above compiles correctly. You may also run your compiled code at this
point, but won’t see anything happen yet (because the main method contains no code).
Write the code for the greet() method:
Put your cursor inside the greet method, and type the yellow highlighted code below. We call this
the body of the greet method. Notice that the non-highlighted code is what you’ve already typed.
Notice also that println stands for “print line”. The character between the t and the n is a
lowercase letter l.
Modify the code so that your name is displayed, instead of Mary Smith’s name.
Save and compile your code, fixing any errors.
Run your code, but you still won’t see anything happen yet.
Why does nothing happen when you run your code?
The reason is that when you run a program, the Java Runtime Environment runs the code that you’ve
written in the body of the main() method. Right now, you have a main() method, but no code in
the body of that method. Once you start putting code in the body of the main() method, then you
will find that your program actually does something when you click “run”.
CSE 174 – Program 1 Page 6
Fixing indentation:
Dr. Java will automatically handle indentation for you as long as you press “enter” at the end of each
line of text that you type. If at any time, you notice that your indentation looks incorrect, use the
following Dr. Java indentation shortcut to fix it:
1. Select all your text. (Ctrl-A in Windows, Command-A on a Mac)
2. Press the “tab” key.
If Dr. Java is still not indenting correctly, there is a good chance that you’ve made an error in your code
(such as missing parentheses, misspelling a Java command, or something similar).
Type the highlighted code for the body of the explainGame() method:
Save and compile your code, fixing any errors.
Type the highlighted code for the body of the printBorder() method:
Save and compile your code, fixing any errors. Note that one of the lines above contains a print()
statement, and the other contains a println() statement. What’s the difference? When you print
with println(), the cursor moves to the next line after it is done printing. When you print with
print(), the cursor stays on the same line when it is done printing.
Looking back:
Recall that this class contains 4 methods. So far, you have written code for three of those methods.
Your program still does nothing when it is “run”, because it lacks any code in the method named
main(). That’s what you still need to do: type the body of the main() method. In doing so, you will
be making use of all of your other methods. Pay attention and you should notice that you will
eventually “call on” the greet(), explainGame() and printBorder() methods as you type
the code for the main() method.
CSE 174 – Program 1 Page 7
Next, write the body of the main() method.
Put your cursor inside the body of the main() method. Since this is a longer method, you should
frequently compile and run your code. Throughout the code, you will see several stars to indicate
that it would be a good idea to save, compile, and run. Don’t move on until the program compiles and
runs correctly at each star. Note that the first three lines below were already typed in a previous step.
(At this point, if you run your program, it should prompt the user for her first and last name, display a
greeting, introduce the game, and ask for her first guess.)
Continued on the next page…
Begin typing here:
CSE 174 – Program 1 Page 8
Don’t type this line…it’s the end of the main()
method, which you’ve typed already.
CSE 174 – Program 1 Page 9
Here’s what a sample run of the program should look like if you run it. (Notice that Mary Smith is a
very lucky guesser.)
Part 3: Submit the current version of your program
Is your program running as expected? If so, then now is a good time to submit your current working
version, even though you will still be making changes. This is a very important step because soon you
will be making several changes to your program. It is good to upload a version you know is working
before you make those changes.
So, prior to making any of the modifications below, go to program1 on the course website and submit
your source code for this assignment. When you do, the website automatically changes the name of
the file. Don’t worry about that. It’s fine. Do not change the name of your file on your computer. It
should be FirstProgram.java at all times, even when you make changes below.
CSE 174 – Program 1 Page 10
Part 4: Modify the program
Now it is time to “play around” with your program. Note that you do not need to do any external
“research” to solve the following (except perhaps for modification #4). Instead, look carefully at the
program you already typed, and learn some techniques from the code you already typed.
Once the program is working correctly, make all four of these modifications:
1. Even though the program prompts the user for her first and last name, it only displays her first
name in the introduction. Don’t change the part of the program that asks the user for her
name, but fix the program so that the greeting displays the user’s first and last name, separated
with a space, rather than just the first name. For example, “Hello Mary Smith,” rather than
“Hello Mary,”). The game introduction should still only display the user’s first name (so, it
should still say, for example, “Let’s play a game, Mary…”.
2. The mystery number should be a random number from 1 to 100, rather than 1 to 50, and in
order to “win” the game, the number must be guessed in fewer than 7 guesses (rather than 6).
Modify any comments in your code to reflect this change.
3. Modify the part of the program that prints the triangle by choosing one of the following
options. Either:
Ask the user how many rows should be in the triangle, and display that many rows. For
example, if the user says 7, then the triangle would display 7 rows of dollar signs, beginning
with 1, then 2, then 3, then 4, then 5, then 6, then 7. OR…
Make the number of rows in the triangle be a random number between 1 and 30. Random
does NOT mean that the programmer should pick her favorite number and put it in the
program. Rather, “random” means that each time your program is run, the computer will
generate a different, unpredictable number of rows in the triangle, with as few as one row,
or as many as thirty rows.
4. Instead of displaying the dollar symbol ($) in the triangle of money, display the cents symbol
(¢). You could search the internet for how to display this symbol. But there are other ways.
What if something goes wrong with your file?
Whenever you upload your work to the course website, you are creating your own personal “backup
copy” of your work. If something should go wrong as you make your modifications, remember that
you can go back to the course website, locate the file you submitted, and download it to your
computer.
Part 5: Submit your modified source code
Once you have made the required modifications to your code, and you find that your code works as
expected, it’s time to re-upload your source code. On the course website, go to program1 and upload
your updated source code file.