import javabook.*;
/*
This is an introductory
first program.
Hopefully it works just
fine!
*/
class HelloWorld
{
public static void main(String[]
args)
{
System.out.println("Hello world!");
System.out.println("This is my first Java program!");
}
}
8. Click the "Compile" button, and wait for it to display an error message
at the bottom or the text "Class compiled - no syntax errors." If there
are any errors, fix them and recompile.
9. When your class has compiled correctly, find the project window
and right-click on the HelloWorld class rectangle.Chose "void main(args)",
which sends a message to the class to run the method called main. When
the "BlueJ: Method Call" window pops up, just click "OK" to send no arguments
to the method.
10. If all went successfully, the BlueJ Terminal Window should pop
up and you should see the text "Hello world!" inside it. Congratulations!
11. What do "/*" and "*/" do?
12. Change the first appearance of the word "println" to "print". What
happens?
13. Close the "Terminal Window" and the "Hello World" Java code window.
Exit BlueJ by clicking on the "Project" menu, then clicking "Quit."
import javabook.*;
/*
This program will allow you to draw a
picture by dragging a mouse while
holding the left button. To erase the
picture, click the right mouse button.
*/
class FunTime
{
public static void main(String[] args)
{
SketchPad doodleBoard;
// Declare SketchPad object named doodleBoard
doodleBoard = new SketchPad();
// Create the SketchPad object
doodleBoard.setVisible(true);
// Make doodleBoard visible
doodleBoard.toFront();
// Make doodleBoard appear in front
}
}
7. Compile your program and fix errors until it compiles successfully.
8. Right-click the "FunTime" class in the project window and choose
"void main(args)" to run the program.
9. If all goes successfully, you should see a SketchPad window in front
of you. Have fun with it! When done, close the window to end the program.
10. What does "//" do? How is it different from "/*" and "*/"?
11. Close the Java source window, if still open, and leave just the
Project window remaining.
// Declare, create, and
display a MessageBox
MessageBox messageBox;
messageBox = new MessageBox(mainWindow);
messageBox.show("I Love
Java!!!");
}
}
2. Compile and run the program. Enter integers when the program asks you to. What does the operation "%" do? How about "/"? (Try running the program several times with different input.)
3. Now change the type of a and b from "int" to "double", and change
the two "getInteger" method calls to "getDouble". Recompile.
How does the behavior of "%" change? Get rid of the "%" line and
recompile.
Question 1: How does the behavior of "/" change?
Question 2: The type "double" is badly named--what does it mean
in this context?
4. Suppose you want to "comment out" a block of code that's bugging
you. That is, you want to make the compiler ignore some code without actually
removing the code from your file. The /*...*/ style comments give you a
convenient tool for doing this. Try commenting out everything in
main.. Recompile.
Question 3: What happens, and why? How can you fix the
problem?
Question 4: Which style of comments is appropriate for documentation
in your code, and which style of comments is appropriate for commenting
out blocks of code at a time?
5. Put the answers to Questions 1-4 in documentation at the top of the program. Add the names of all students in your group.
6. Submit this program electronically. To find out how to do so, go to the class home page at http://www.mathcs.carleton.edu/faculty/dmusican/cs117f01 and click on the link "Electronically submitting your work."
fahrenheit = 1.8 x celsius + 32
Make sure to add the names of all students in your group to documentation at the top of the program, and electronically submit your work.