Programming Assignment in Java

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CMPS 12M

Data Structures Lab

Lab Assignment 1

The purpose of this assignment is threefold: (1) get a basic introduction to the Andrew File System (AFS)

which is the file system used by the ITS unix timshare, (2) learn how to create an executable jar file

containing a Java program, and (3) learn to automate compilation and other tasks using Makefiles.

AFS

Logon to your ITS unix timeshare account at unix.ucsc.edu. If you don't know how to do this, ask for

help at a lab session, or see Lab Assignment 1 from my CMPS 12A/L Spring 2018 webpage:

https://classes.soe.ucsc.edu/cmps012a/Spring18/lab1.pdf

Create a subdirectory within your home directory called cs12b in which you will keep all your work for

both CMPS 12B and CMPS 12M. Create a subdirectory within cs12b called lab1. From within lab1

create a subdirectory called private, then set access permissions on the new directory so that other users

cannot view its contents. Do all this (starting in your home directory) by typing the lines below. The unix

prompt is depicted here as %, although it may look different in your login session. The lines without the

unix prompt are the output of your typed commands.

% mkdir cs12b

% cd cs12b

% mkdir lab1

% cd lab1

% mkdir private

% fs setacl private system:authuser none

% fs listacl private

Access list for private is

Normal rights:

foobar rlidwka

Here foobar will be replaced by your own cruzid. The last line of output says that your access rights to

directory private are rlidwka which means: read, list, insert, delete, write, lock, and administer. In

other words you have all rights in this directory, while other users have none. If you are unfamiliar with

any unix command, you can view its manual page by typing: man <command name>. (Do not type the

angle brackets <>.) For instance man mkdir brings up the man pages for mkdir. Man pages can be very

cryptic, impenetrable even, especially for beginners, but it is best to get used to reading them as soon as

possible. Under AFS, fs denotes a file system command, setacl sets the access control list (ACL) for a

specific user or group of users, and listacl displays the access lists for a given directory. The command

% fs setacl <some directory> <some user> <some subset of rlidwka or all or none>

sets the access rights for a directory and a user. Note that setacl can be abbreviated as sa and listacl

can be abbreviated as la. For instance do la on your home directory:

% fs la ~

Access list for /afs/cats.ucsc.edu/users/a/foobar is

Normal rights:

foobar rlidwka

system:authuser l

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The path /afs/cats.ucsc.edu/users/a/foobar will be replaced by the full path to your home

directory, and your own username in place of foobar. Note that ~ (tilde) always refers to your home

directory, . (dot) always refers to your current working directory (the directory where you are currently

located) and .. (dot, dot) refers to the parent of your current working directory. The group

system:authuser refers to anyone with an account on the ITS unix timeshare. Thus by default, any

user on the system can list the contents of your home directory. No other permissions are set for

system:authuser however, so again by default, no one else can read, insert, delete, write, lock, or

administer your files.

Do fs la ~/cs12b and verify that the access rights are the same for the child directory cs12b as for its

parent, your home directory. Create a subdirectory of private, call it anything you like, and check its

access rights are the same as for its parent. Thus we see that child directories inherit their permissions from

the parent directory when they are created. To get a more comprehensive list of AFS commands do fs

help. For instance you will see that fs lq shows your quota and usage statistics. For more on the

Andrew File System go to

https://en.wikipedia.org/wiki/Andrew_File_System.

Note: Some users may see the group system:anyuser in place of system:authuser when they do the

above commands. This is because newer accounts were created with slightly different ACLs than older

accounts. Whatever the ACL is for ~/cs12b/private, set it so that you have all rights, and other users

have no rights. The distinction between the user groups system:authuser and system:anyuser is of

no significance to us.

Jar Files

Copy the following file to your lab1 directory. (You can find this file in the Examples section of the

class webpage.)

// HelloUser.java

// Prints greeting to stdout, then prints out some environment information.

class HelloUser{

public static void main( String[] args ){

String userName = System.getProperty("user.name");

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 javaHome = System.getProperty("java.home");

long freemem = Runtime.getRuntime().freeMemory();

long time = System.currentTimeMillis();

System.out.println("Hello "+userName);

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: "+javaHome);

System.out.println("Free memory: "+freemem+" bytes");

System.out.printf("Time: %tc.%n", time);

}

}

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You can compile this in the normal way by doing javac HelloUser.java then run it by doing the

command java HelloUser. Java provides a utility called jar for creating compressed archives of

executable .class files. This utility can also be used to create an executable jar file that can then be

run by just typing its name at the unix prompt (with no need to type java first). To do this you must first

create a manifest file that specifies the entry point for program execution, i.e. which .class file contains

the main() method to be executed. Create a text file called Manifest containing just one line:

Main-class: HelloUser

If you don’t feel like opening up an editor to do this you can just type

% echo Main-class: HelloUser > Manifest

The unix command echo prints text to stdout, and > redirects the output to a file. Now do

% jar cvfm HelloUser Manifest HelloUser.class

The first group of characters after jar are options. (c: create a jar file, v: verbose output, f: second argument

gives the name of the jar file to be created, m: third argument is a manifest file.) Consult the man pages to

see other options to jar. The second argument HelloUser is the name of the executable jar file to be

created. The name of this file can be anything you like, i.e. it does not have to be the same as the name of

the .class file containing function main(). For that matter, the manifest file need not be called Manifest, but this is the convention. Following the manifest file is the list of .class files to be archived.

In our example this list consists of just one file: HelloUser.class. At this point we would like to run

the executable jar file HelloUser by just typing its name, but there is one problem. This file is not

recognized by Unix as being executable. To remedy this do

%chmod +x HelloUser

As usual, consult the man pages to understand what chmod does. Now type HelloUser to run the program.

The whole process can be accomplished by typing five lines:

% javac –Xlint HelloUser.java

% echo Main-class: HelloUser > Manifest

% jar cvfm HelloUser Manifest HelloUser.class

% rm Manifest

% chmod +x HelloUser

Notice we have removed the now unneeded manifest file. Note also that the –Xlint option to javac enables

recommended warnings. The only problem with the above procedure is that it’s a big hassle to type all

those lines. Fortunately there is a unix utility that can automate this and other processes.

Makefiles

Large programs are often distributed throughout many files that depend on each other in complex ways.

Whenever one file changes all the files depending on it must be recompiled. When working on such a

program it can be difficult and tedious to keep track of all the dependencies. The Unix make utility

automates this process. The command make looks at dependency lines in a file named Makefile. The

dependency lines specify relationships between source files by indicating a target file that depends on one

or more prerequisite files. If a prerequisite has been modified more recently than its target, make updates

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the target file based on construction commands that follow the dependency line. make will normally stop

if it encounters an error during the construction process. Each dependency line has the following format.

target: prerequisite-list

construction-commands

The dependency line is composed of the target and the prerequisite-list separated by a colon. The

construction-commands may consist of more than one line, but each line must start with a tab

character.

Start an editor and copy the following lines into a file called Makefile.

#------------------------------------------------------------------------------

# A simple Makefile

#------------------------------------------------------------------------------

HelloUser: HelloUser.class

echo Main-class: HelloUser > Manifest

jar cvfm HelloUser Manifest HelloUser.class

rm Manifest

chmod +x HelloUser

HelloUser.class: HelloUser.java

javac -Xlint HelloUser.java

clean:

rm -f HelloUser HelloUser.class

submit: README Makefile HelloUser.java

submit cmps012b-pt.w19 lab1 README Makefile HelloUser.java

Anything following # on a line is a comment and is ignored by make. The second line says that the target

HelloUser depends on HelloUser.class. If HelloUser.class exists and is up to date, then

HelloUser can be created by doing the construction commands that follow. Remember that all indentation

is accomplished via the tab character. The next target is HelloUser.class which depends on

HelloUser.java. The next target clean is what is sometimes called a phony target since it doesn’t

depend on anything and just runs a command. Likewise the target submit does not compile anything, but

does have some dependencies. Any target can be built (or executed if it is a phony target) by doing make

<target name>. Just typing make creates the first target listed in the Makefile. Try this by doing make

clean to get rid of all your previously compiled stuff, then do make again to see it all created again.

Your output from make should look something like:

% make

javac -Xlint HelloUser.java

echo Main-class: HelloUser > Manifest

jar cvfm HelloUser Manifest HelloUser.class

added manifest

adding: HelloUser.class(in = 1577) (out= 843)(deflated 46%)

rm Manifest

chmod +x HelloUser

The make utility allows you to create and use macros within a Makefile. The format of a macro definition

is ID = list where ID is the name of the macro (by convention all caps) and list is a space separated

list of filenames. Then the expression $(list) below the definition in the Makefile, refers to this list of

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files. Move your existing Makefile to a temporary file, then start your editor and copy the following lines

to a new file, again called Makefile.

#------------------------------------------------------------------------------

# Another Makefile with macros

#------------------------------------------------------------------------------

JAVASRC = HelloUser.java

SOURCES = README Makefile $(JAVASRC)

MAINCLASS = HelloUser

CLASSES = HelloUser.class

JARFILE = HelloUser

SUBMIT = submit cmps012b-pt.w19 lab1

all: $(JARFILE)

$(JARFILE): $(CLASSES)

echo Main-class: $(MAINCLASS) > Manifest

jar cvfm $(JARFILE) Manifest $(CLASSES)

rm Manifest

chmod +x $(JARFILE)

$(CLASSES): $(JAVASRC)

javac -Xlint $(JAVASRC)

clean:

rm $(CLASSES) $(JARFILE)

submit: $(SOURCES)

$(SUBMIT) $(SOURCES)

Notice that the definition of a macro can contain other macros in its right hand side, as in the list SOURCES

above. Run this new Makefile and observe that it is equivalent to the previous one. The macros define text

substitutions that happen before make interprets the file. Study this new Makefile until you understand

exactly what substitutions are taking place. Now create your own Hello program and call it

HelloUser2.java. It can say anything you like, but just have it say something different from the original.

Add HelloUser2.java to the JAVASRC list, add HelloUser2.class to the CLASSES list and change

MAINCLASS to HelloUser2. Also change the macro JARFILE to just Hello (emphasizing that the jar

file can have any name.) Remember that all indentation in a Makefile must be accomplished with the tab

character, not spaces, or the make utility will not work.

#------------------------------------------------------------------------------

# Yet another Makefile with macros

#------------------------------------------------------------------------------

JAVASRC = HelloUser.java HelloUser2.java

SOURCES = README Makefile $(JAVASRC)

MAINCLASS = HelloUser2

CLASSES = HelloUser.class HelloUser2.class

JARFILE = Hello

SUBMIT = submit cmps012b-pt.w19 lab1

all: $(JARFILE)

$(JARFILE): $(CLASSES)

echo Main-class: $(MAINCLASS) > Manifest

jar cvfm $(JARFILE) Manifest $(CLASSES)

rm Manifest

chmod +x $(JARFILE)

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$(CLASSES): $(JAVASRC)

javac -Xlint $(JAVASRC)

clean:

rm $(CLASSES) $(JARFILE)

submit: $(SOURCES)

$(SUBMIT) $(SOURCES)

This new Makefile compiles both HelloUser classes (even though neither one depends on the other.) Notice

however the entry point for program execution has been changed to function main() in your program

HelloUser2.java. Macros make it easy to make changes like this, so learn to use them. To learn more

about Makefiles follow the links posted on the class webpage.

We've discussed three Makefiles in this project. If you rename them Makefile1, Makefile2 and

Makefile3 respectively (since you can't have three files with the same name), you'll find that the make

command does not work since a file called Makefile no longer exists. Instead of renaming files to run

the Makefile you want, you can use the -f option to the make command, and specify the name of your

Makefile. For instance

% make -f Makefile2

runs Makefile2. If you want to specify something other than the first target, place it after the file name

on the command line. For instance

% make –f Makefile3 clean

runs the clean target in Makefile3.

What to turn in

All files you turn in for this and other assignments (in both 12B and 12M) should begin with a comment

block giving your name, cruzid, class (12B or 12M), date, a short description of its role in the project, the

file name and any special instructions for compiling and/or running it. Create one more file called

README which is just a table of contents for the assignment. In general README lists all the files being

submitted (including README) along with any special notes to the grader. Use what you've learned in

this project to write a Makefile that creates and archives both .class files (HelloUser.class and

HelloUser2.class) in an executable jar file called Hello, and that runs function main() from

HelloUser2.class. It should also include clean and submit utilities, as in the above examples. Also

add a check utility that checks that the project was properly submitted.

See the webpage for instructions on using the submit command and for checking that a project was

properly submitted. Submit the following files to the assignment name lab1:

README described above

Makefile described above

HelloUser.java unchanged from above

HelloUser2.java described above

You can either type the submit command directly:

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% submit cmps012b-pt.w19 lab1 README Makefile HelloUser.java HelloUser2.java

or use the Makefile itself:

% make submit

This is not a difficult assignment, especially if you took CMPS 12A from me (see lab4 from the Spring

2018 offering of that class), but start early and ask questions if anything is unclear.