Laboratory 0: Linux Operating System and Java

January 24, 25, 2006

Objectives

1. to familiarize yourself with the Linux operating system,
2. to provide practice editing, compiling, running and revising a Java application.

1. Introduction

2. Logging in

3. The Firefox web browser

http://www.cs.trincoll.edu/~cpsc115/

4. Creating a cpsc115 directory

5. File and directory access permissions

• The user who owns the file (designated with 'u').
• The users in the group to which the file belongs (designated with 'g').
• All users (designated with 'o').

• Read (designated with 'r'): It allows to examine the content of the file.
• Write (designated with 'w'): It allows to modify the content of the file.
• Execute (designated with 'x'): It allows to run the file as a command.

• Read (designated with 'r'): It allows to list the content of the directory.
• Write (designated with 'w'): It allows to add or remove files in the directory.
• Execute (designated with 'x'): It allows to access the files and subdirectories in the directory.

1. Right-click on the cpsc115 folder.
2. Select Properties -> Permissions.
3. For Owner, select Can View & Modify Content.
4. For Group, select Forbidden.
5. For Others, select Forbidden.
6. Click OK.

6. The KWrite text editor

1. Copy the following text and Paste it into the blank KWrite window. You can also type the text but make sure to enter exactly as shown.

   public class HelloWorld {
     public static void main(String args[]) {
       System.out.println("Hello World!");
     }
   }
   

2. Select File -> Save As to save the file in your cpsc115 directory. Name the file as HelloWorld.java. Notice that the name of the Java file and the name of the Java class are identical.

7. Compiling and running the HelloWorld.java application

1. cd - This command changes the working directory to the one specified. Set the working directory to cpsc115 by entering the following.
   
   cd cpsc115
   
   
2. javac - This command compiles the application into Java bytecode and then save the compiled file with the .class extension. Compile your Java source file by entering the following.
   
   javac HelloWorld.java
   
   
3. java - This command interprets the Java bytecode of a compiled file and produces an output. Run your program by entering the following.
   
   java HelloWorld

8. Editing and re-running the HelloWorld.java application

1. Open the source code HelloWorld.java by clicking anywhere inside the KWrite window. The program contains the following code:

   public class HelloWorld {
     public static void main(String args[]) {
       System.out.println("Hello World!");
     }
   }
   

   Change "Hello World!" to some other message by editing the System.out.println() statement on line 3. Select File -> Save to save the updated file. Re-run the program.
   
   
2. Notice that the name of the class in HelloWorld.java is HelloWorld. The rule in Java is that the Java source file must have exactly the same name as the class the file contains.
   
   Change the name of the class in HelloWorld.java to TrivialApplication, save the updated file, and then try to re-run the program.
   
   A system error will occur when Java tries to load the TrivialApplication class into memory but cannot find it. You can fix this error by changing the class's name back to HelloWorld. Save the updated file and re-run the program.
   
   
3. A syntax error is an error generated by the compiler when it cannot correctly parse your source program. There are lots of ways to generate a syntax error: misspelling Java keywords, forgetting to declare a variable before using it, misspelling a previously declared identifier, even forgetting a semicolon at the end of a statement, etc.
   
   Delete the semicolon after the System.out.println() statement and then re-run the program.
   
   This time you should get an error message:

   HelloWorld.java:4: ';' expected
     }
     ^
   1 error
   

   Add a semicolon and run your program again.

9. What are unethical bahaviors involving computers?

1. breaking into a room or office,
2. going through someone's desk,
3. vandalism,
4. harrassment,
5. plagiarizing.

10. Optional exercises

http://www.cs.trincoll.edu/~pyoon/unixtut/

What to hand in

CPSC 115L home page