Introduction to Programming Lab Assignment 1 Solution

The purpose of this assignment is threefold: get a basic introduction to the Unix operating system, to learn how to create and edit text files using either the Vi or Emacs text editors, and to learn to compile and run a Java program.




Preparation




Before attempting this assignment, begin reading one of the Unix tutorials linked on the course website. You need not complete the tutorial, but find one that you like, start it and bookmark it for future reference. Vi and Emacs are two very popular text editors available on all Unix systems. Also start reading one of the Vi tutorials, or the Emacs tutorial that are linked on the course website.




Unix




In order to submit any work in this class, you must first logon to your Unix Timeshare account (unix.ucsc.edu). For those running any version of Windows, you can do this by downloading a program called PuTTy. Go to http://www.chiark.greenend.org.uk/~sgtatham/putty/download.html, download and then run the file putty.exe. Fill in unix.ucsc.edu as the Host Name, 22 as the port number, SSH as the connection type, then press open. Type your CruzID at the login prompt and give your Blue password. If you are running either Mac OSX or Linux, open a terminal window and type the command:




ssh cruzid@unix.ucsc.edu




where cruzid is your CruzID, then respond with your Blue password. If all this was done correctly you are now logged on to the Unix Timeshare. You will see a prompt that most likely looks like: bash-4.1$. This is the Unix command prompt which indicates that the command interpreter is waiting for you to type a command. In the examples that follow I will represent this prompt by the single character: %. If any of the above steps failed and you cannot logon, you'll need to attend a lab session and get help.




Type ls to list the contents of your home directory. Use the command mkdir to create a new directory called cs12a in which you will place all work for this class. Type ls again to see the new cs12a directory listed. Make cs12a your current working directory by typing cd cs12a at the command prompt.




ls
mkdir cs12a
ls
cd cs12a



Remember that % here represents the Unix command prompt and you do not type it. You can learn about any Unix command by typing man at the command prompt. Try:




man mkdir



man ls
man cd
man man



Man pages are notorious for being cryptic and even impenetrable, especially for beginners. Typically, they assume a great deal of background knowledge. Nevertheless, you must get used to reading them since they are an invaluable resource. Use the man pages in conjunction with the tutorial to build up your vocabulary of Unix commands. Also try using Google to find Unix commands. For instance, a Google




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search on the phrase “unix copy” brings up a reference to the cp command. Research the following Unix commands, either through the tutorial, or man pages, or Google: man, ls, pwd, cd, mkdir, more, less, cp, cat, rm, rmdir, mv, echo, date, time, alias, history. You can also try just typing the command and see what happens. Create a subdirectory of cs12a called lab1 and cd into it, then type pwd to confirm your location.




mkdir lab1
cd lab1
pwd



The output of the last command should look something like




/afs/cats.ucsc.edu/users/f/cruzid/cs12a/lab1




where cruzid is your CruzID and the letter f may be different for you. This is the full path name of your current working directory. See http://docstore.mik.ua/orelly/unix2.1/lrnunix/ch03_01.htm for more on the Unix directory structure. It is highly recommended that you create separate subdirectories of cs12a for every lab and programming assignment in this class.




Editors




Using either the Vi or Emacs text editor create a file in your lab1 directory called HelloWorld.java containing the following lines. This file can be found on the course website under Examples/lab1.




HelloWorld.java class HelloWorld{



public static void main(String[] args){ System.out.println("Hello, world!");




}

}




This is a Java source file. Close the editor and type more HelloWorld.java at the command prompt to view the contents of the file.




Java




In order to run the program, we must first compile it. A compiler is a program that translates source code into executable code, which is what the computer understands. To compile the above program type




% javac HelloWorld.java




You should see the unix prompt (%) disappear for a few seconds while it works, then reappear. List the contents of lab1 again to see the new file HelloWorld.class. This is a Java executable file. You can now run the program by typing




% java HelloWorld




This command should cause the words




Hello, world!




to be printed to the screen, followed by a new command prompt on the command line. We will have a lot more to say about the proper use and syntax of the Java programming language, but for now just note that what is printed to the screen is exactly what appears between quotes in the line




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System.out.println("Hello, world!");




in the source file HelloWorld.java. Also note that everything after // on a line constitutes a comment and is ignored by the compiler. Every program you write in this class must begin with a comment block of the following form.




filename
your Name
your CruzID
the assignment name (like lab1 or pa1)
a very short description of what the program does



Open up your editor and change the comment block in HelloWorld.java to conform to the above format.

Also change the body of the program so that it prints out your name:




Hello, my name is Foo Bar.




where Foo is your first name and Bar is your last name. Compile the new program and run it. If it does not compile, i.e. if you get error messages when you run javac, look for some stray character that you might have inserted into the file inadvertently, or perhaps a required character you failed to type.




Now create a new text file called HelloWorld2.java containing the lines




HelloWorld2.java



your Name
your CruzID
lab1



prints greeting and some system information. class HelloWorld2{



public static void main( String[] args ){ String os = System.getProperty("os.name"); String osVer = System.getProperty("os.version"); String jre = System.getProperty("java.runtime.name");




String jreVer = System.getProperty("java.runtime.version"); String jvm = System.getProperty("java.vm.name");




String jvmVer = System.getProperty("java.vm.version"); String home = System.getProperty("java.home"); double freemem = Runtime.getRuntime().freeMemory(); long time = System.currentTimeMillis();




System.out.println("Hello, World!"); System.out.println("Operating system: "+os+" "+osVer); System.out.println("Runtime environment: "+jre+" "+jreVer); System.out.println("Virtual machine: "+jvm+" "+jvmVer); System.out.println("Java home directory: "+home); System.out.println("Free memory: "+freemem+" bytes"); System.out.printf("Time: %tc.%n", time);




}

}




Compile and run this program by doing




javac HelloWorld2.java
java HelloWorld2






3

You will see that it prints something like




Hello, World!

Operating system: Linux 2.6.32-504.12.2.el6.x86_64

Runtime environment: OpenJDK Runtime Environment 1.7.0_75-mockbuild_2015_01_20_23_39-b00

Virtual machine: OpenJDK 64-Bit Server VM 24.75-b04

Java home directory: /usr/lib/jvm/java-1.7.0-openjdk-1.7.0.75.x86_64/jre

Free memory: 1.22431496E8 bytes

Time: Sun Mar 29 14:05:04 PDT 2015.




The exact output you get will depend on the date and time you run it, as well as the platform you are working on. You can see that the extra lines in this version of the program have the effect of collecting and printing certain platform specific information. The meaning of these lines may be discussed in class at some point.




Now edit this file once more so that the comment block contains your name and CruzID, and alter the greeting so that it prints




Hello, my name is Foo Bar




where Foo Bar is your name, as before. Recompile your program, wring out any typographical errors you might find, then test it.




What to turn in




Read the instructions on the website concerning the use of the submit command. Briefly, the syntax of the submit command is




% submit class_name assignment_name file1 file2 file3 …




Here class_name will be cmps012a-pt.w16 for all Lab and Programming assignments you turn in. The assignment_name in this case is lab1. Submit the two source files HelloWorld.java and HelloWorld2.java. Thus your submit command will be




% submit cmps012a-pt.w16 lab1 HelloWorld.java HelloWorld2.java




This command must be typed from within your lab1 directory where these source files reside, or you will get error messages. Start early and ask questions in the lab sessions or office hours if anything is unclear.