COM 1205 Programming Assignment 4

Due: February 6, 2001

We are taking an incremental approach to adaptive software development in this course: In hw 1 you read and analyzed Java programs, in hw 2 you filled in missing information in Java programs that use DJ, in hw 3 you modified programs that use class dictionaries (similar to XML schemas) and a tiny bit of DemeterJ (the weaving feature offered by Class1 { {{ ... }} } Class2 { {{ ... }} } ... ).

Now in hw 4 you write a simple Java program using DJ and a tiny bit of DemeterJ (the weaving feature) from scratch but you are given the class dictionary.

This homework has two parts: The first part is the Laboratory Guide and the second part is a simple UNIX shell. The Laboratory Guide introduces you to DemeterJ (formerly called Demeter/Java) but most of what you learn will help you to write Java Programs with DJ and a tiny bit of DemeterJ. So when you go through the Laboratory Guide, focus on class dictionaries and how you would express the adaptive programs you encounter directly using DJ without using the adaptive programming language of DemeterJ.

Name substitution throughout Laboratory Guide and other documents:
Demeter/Java -> DemeterJ
demjava -> demeterj

THEMES:

Laboratory Guide: An interesting example of adaptive programming in Java (Lab Guide).
Simple Unix shell in DJ with weaving and code generation from class dictionary by DemeterJ. This second part is significantly more challenging than the the previous homeworks. If you cannot do it completely, apply the Growth Plan Pattern and turn in the last phase you could complete.

READING:

Read chapters 8, 11, 12 of the AP book.

The class dictionary for DemeterJ which defines the DemeterJ notation. It is reachable from the DemeterJ and AP-Studio resources page: http://www.ccs.neu.edu/research/demeter/DemeterJava/

Plus additional reading as described below.

PART 1:

PURPOSE: See DemeterJ in action. Study an application of the concepts covered so far in the context of a Java application.

Tasks to be done: Read and work through the Laboratory Guide using DemeterJ and hand in all files modified.

Browse through the DemeterJ User's Guide available from the DemeterJ and AP-Studio Resources page http://www.ccs.neu.edu/research/demeter/DemeterJava/. Focus on class dictionaries and pnly a little bit on the adaptive programming language of DemeterJ.

Browsing the User's Guide will help you to better understand the Laboratory Guide available from the same resource page.

The purpose of this laboratory exercise is to see adaptive programming in operation in the Java world.

Corrections to the Laboratory Guide:

None at the moment.

Please send mail to 

lieber@ccs.neu.edu johan@ccs.neu.edu 

if you find something not clear in the Laboratory Guide.

From a happy user of the Demeter/C++ lab guide. The DemeterJ Laboratory Guide is a translation of the Demeter/C++ Lab Guide.

Hi Crista:
 
I just finished working through the Demeter Lab Guide and already feel
a lot more comfortable with Demeter. The Lab Guide is concise, clear
and written with a great deal of empathy for the user. Congratulations
for doing such an excellent job with the Lab Guide!
 
...

PART 2:

We simulate a few Operating System file management commands by building our own data structures that represent what the commands do. You are not allowed to use Runtime and Process objects in this homework. Your program should be able to handle inputs like:

mkdir a
mkdir b
cd a
mkdir c
mkdir d
cd d
mkdir x
cd ..
cp -r d e
cd ..
echo "before du"
du
find . -name x -print

and produce the same output as UNIX, except that the disk usage command du prints only the file structure and no sizes. More precisely, your program should be able to execute a list of commands as defined by the Extended Backus-Naur-Form (EBNF) grammar below (in Demeter class dictionary notation):

The following misses the part names < ... >. The full cd is here:
Full cd.

FileSystem = CompoundFile EOF.
File : SimpleFile | CompoundFile common  FileName.
SimpleFile = "simple".
CompoundFile = "compound"  PList(File). 

Commands = List(Command) EOF.
Command : Simple.
Simple : MakeDirectory | ChangeDirectoryUp | ChangeDirectoryDown |
RecursiveCopy | DiskUsage | Find | Echo |
SymbolicLink | RemoveDirectory | CreateEmptyFile | RemoveFile.
MakeDirectory = "mkdir" DirectoryName.
ChangeDirectoryUp = "cd ..".
ChangeDirectoryDown = "cd" DirectoryName.
RecursiveCopy = "cp -r"  DirectoryName  DirectoryName.
DiskUsage = "du .".
SymbolicLink = "ln -s"  FileName  FileName.
RemoveDirectory = "rmdir" DirectoryName.

// "touch f" creates an empty file called f.
CreateEmptyFile = "touch" FileName.
RemoveFile = "rm" FileName.

Find = "find . -name" DirectoryName "-print".

Echo = "echo" Message.

FileName = Ident.
DirectoryName = Ident.
Message = String.

PList(S) ~ "(" {S} ")".
List(S) ~ {S}.

Main = .

For the input above, your program should produce an output similar to:

before du
      ./a/c
      ./a/d/x
      ./a/d
      ./a/e/x
      ./a/e
      ./a
      ./b
      ./
      .
./a/d/x
./a/e/x

It is important to do this part in stages. You get full credit if your program works correctly for the sublanguage that includes the commands

Simple = MakeDirectory | ChangeDirectoryUp | ChangeDirectoryDown | 
DiskUsage | RecursiveCopy | Find | CreateEmptyFile.

It is recommended that you start with primitive commands like CreateEmptyFile, MakeDirectory, ChangeDirectoryUp, ChangeDirectoryDown. Hint: Try to use the CopyVisitor of DemeterJ to do the copying: CompoundFile{ traversal toAll(UniversalVisitor) { to *;} public CompoundFile copy() {{ CopyVisitor cv = new CopyVisitor(CompoundFile.class); this.toAll(cv); return (CompoundFile) cv.get_return_val(); }} } For example, for the input:

mkdir a 
mkdir b
cd a
mkdir c 
mkdir d 
cd .. 
du

your program should produce the output:

      ./a/c
      ./a/d
      ./a
      ./b

But you should write your program in such a way that it would be easy to add the rest of the commands. Note that RecursiveCopy, DiskUsage and Find have significant common behavior that you should factor out.

You should focus your efforts on correct inputs as described by the above grammar. It is not important that you give a good error message in case of a syntax error. But your program needs to handle correct inputs correctly.

To represent your file system you may want to use Java classes similar to the ones described below.

FileSystem =  CompoundFile EOF.
File : SimpleFile | CompoundFile common  FileName.
SimpleFile = "simple".
CompoundFile = "compound"  PList(File).

Solution approach: Use the data-binding approach of DemeterJ to generate Java class definitions and parser and pretty printer from a schema (class dictionary).

Start with the DemeterJ program in $SD/hw/4/os and add more behavior files to the program. For illustration purposes, I constructed a FileSystem-object manually and I printed it out with the display method. Use DemeterJ in the limited way as shown in the previous homework: (e.g. in $SD/hw/3/onlyDJ-average-default-list).

Write your schema in a os.cd file. Define all your visitor classes in your .cd file and make them inherit from class Visitor. Put "import edu.neu.ccs.demeter.dj.*;" as the first line in your .cd file. Define the parts of your visitors in the .beh file or in the .cd file. Use the DemeterJ User Manual http://www.ccs.neu.edu/research/demeter/DemeterJava/UserManual/node2.html to learn to write class dictionaries for DemeterJ. Specifically, the LL(1) section "How to Make a Class Dictionary LL(1)" is important.
Write your behavior files using the pattern:
```
A {
  {{
    // in plain Java:
    // any additional instance variables
    // any additional methods
  }}
}
B {
  {{
    // in plain Java:
    // any additional instance variables
    // any additional methods
  }}
}

// etc.
```
In the Java methods you use DJ to program adaptively. Note that if a method needs additional instance variables, you may introduce them in your behavior file as shown above. This does not allow you to parse or print those variables. If you need that capability (which is rare), you need to introduce your instance variables in your .cd file.
Practice good separation of concerns. Each requirement of the form: "Implement Behavior X" should be ideally implemented in one behavior file. When the requirement changes, we should ideally only have to change the corresponding behavior file.
DemeterJ generates several Visitor classes from the class dictionary. If you want to use those visitors you need to know a little bit of DemeterJ behavior file syntax. If you want to have a print method for class "Commands", create a file print.beh: Commands { void print() to * (PrintVisitor); } and add print.beh to the list of behavior files in your *.prj file. The meaning of the above method is: traverse to all objects reachable from the current Commands-object and use the PrintVisitor as visitor. The directory $SD/hw/4/visitor-usage contains examples how to use the various visitors. The detailed documentation is in the DemeterJ user manual.