Espresso: A Concentrated Introduction to Java

An Introduction to Java

Summary: In this laboratory, you will run and modify your first Java programs.

Contents

• Exercises
  • Exercise 0: Preparation
  • Exercise 1: Starting Eclipse
  • Exercise 2: Your First Program
  • Exercise 3: Your Second Program
  • Exercise 3: print vs. println
  • Exercise 4: print, revisited
  • Exercise 5: Shorthand

Exercises

Exercise 0: Preparation

a. Review An Introduction to Java, Packages in Java, and Java Programming in Eclipse.

b. Create any of the following directories that do not yet exist.

• /home/username/CSC152
• /home/username/CSC152/Code
• /home/username/CSC152/Eclipse
• /home/username/CSC152/First
• /home/username/CSC152/First/username
• /home/username/CSC152/First/username/introjava

c. Make a copy of First.java in that final directory. The easiest way to make a copy is to select the link with the right mouse button (click and hold on a Mac) and select Save Link As ..., then select the directory.

d. Using gedit, add /opt/jdk1.5.0/bin to the line in /home/username/.bash_profile which reads PATH=somestuff. Afterwards, the line should read something like

PATH="/opt/jdk1.5.0/bin:/bin:/usr/bin:/usr/X11R6/bin:/usr/local/bin:/net/bin:."

e. Using gedit, add the following line to your /home/username/.bashrc file.

alias eclipse="/home/rebelsky/bin/eclipse/ &"

f. Open a new terminal window so that those changes take effect. Type

source /home/username/.bash_profile
source /home/username/.bashrc

In the future, you should not have to type that stupid command, but it's a good idea to do so the first time you change your bash profile.

Exercise 1: Starting Eclipse

a. Type eclipse to start Eclipse. Wait. Wait some more. If you see a Welcome screen, click the close box (the x) in the Welcome tab.

b. From the File menu, select New and then Project.

c. In the dialog box that appears, select Java Project and then click Next.

d. In the dialog box that appears, type First as the project name, select Create Project from Existing Source, and type /home/username/CSC152/First as the directory. Under JDK Compliance set the default compliance to 5.0.

e. Click Finish. Wait. You are now ready to program in Java.

Exercise 2: Your First Program

a. Click the arrow next to First in the package explorer so that it points down.

b. Double click on First.java. If all goes well, that should open the program in the edit window.

c. Modify First.java so that it uses the appropriate package name.

d. From the Run menu, select Run As and then Java Application.

e. Confirm that the output (at the bottom of the screen) is Hello.

f. Marvel at all the work it took to get one word printed.

g. Change the Hello in First.java to a word or phrase of your choice.

h. Save the modified file, using Save from the File menu.

i. Try running it to see if it works correctly.

Exercise 3: Your Second Program

a. Make a copy of First.java called Second.java by selecting Save As... from the file menu. Do not make any changes.

b. Click on the Problems tab at the bottom of the screen. What do you see?

c. Modify Second.java so that you can run it. Remember that the name of a class must match the name of the file.

d. Modify Second.java so that it prints two lines.

Hello
Goodbye

Exercise 3: print vs. println

a. Presumably you have two calls to println in Second.java. Replace the first println with print.

b. What effect do you expect this change to have?

c. Verify your prediction experimentally.

Exercise 4: print, revisited

a. Change the second println in Second.java to print.

b. What effect do you expect this change to have?

c. Verify your prediction experimentally.

d. You are likely to get a different result than you expect. Try adding the command pen.flush() after the two calls to pen.print(...) and see what difference this makes.

e. Replace the call to pen.flush() with pen.close(). Rerun the program to see what difference that change makes.

e. Read the documentation for flush. Read the documentation for close.

Praise the authors for their clarity.

f. If possible, explaine the difference between flush and close.

g. If you don't understand what's happened in this exercise, please discuss it with your teacher or lab assistant.

Exercise 5: Shorthand

As you may have noticed, it can get irritating to type the full name of a class each time you use the class. Hence, the designers of Java included a shorthand mechanism that lets you type only the basic class name. To use this shorthand, you must include a line at the top of your program (after the package declaration) of the form

import packagename.ClassName;

You may then use just ClassName in the rest of the program.

a. Replace all instances of java.io.PrintWriter in Second.java with PrintWriter. Do not add the import statement above. What do you expect to happen when you try to compile and run Second?

b. Verify your answer experimentally.

c. Add the import statement and try again.

History

Sunday, 30 January 2005 [Samuel A. Rebelsky]

• Created.

Monday, 31 January 2005 [Samuel A. Rebelsky]

• Added a few more instructions based upon student experience.

Wednesday, 31 August 2005 [Samuel A. Rebelsky]

• A few minor modifications.

Friday, 2 September 2005 [Samuel A. Rebelsky]

• Removed file output exercises.

Friday, 27 January 2006 [Samuel A. Rebelsky]

• Began update for Eclipse (ouch!).

Sunday, 29 January 2006 [ Samuel A. Rebelsky]

• Finished update for Eclipse.

Thursday, 30 March 2006 [Samuel A. Rebelsky]

• Minor edits.