LAMP: Compilation

Computer Science Department
Programming Methods Laboratory

Compilation summer 01

Java/JLex/JavaCup - HOWTO

As you may already know, Java organizes a program into classes, with each class in a program compiled into a separate binary object code file (.class files).

It is good practice to separate the source code (in .java files) from the Java classfiles. A good way to do it is to create in your compilation directory a sources directory and a classes directory.

The directory in which source files (.java files) should be stored is compilation/sources/filter.
The directory into which class files (.class files) are compiled is compilation/classes.

javac is the Java compiler that you will use during the project.

DESTINATION

By default, javac places the class files it generates in the same directory as the corresponding source file. To override this behavior, use the -d option.

The -d directory option will make the specified directory the root of the class hierarchy. All the .class files are then placed in this directory, or in the appropriate subdirectory below it, depending on the package name of the class.

Example:

    javac -d ~/compilation/classes ~/compilation/sources/filter/Toto.java

creates a classfile for the sourcefile Toto.java in the directory compilation/classes.

When the -d option is specified, javac automatically creates any directories it needs to store its class files in the appropriate place.

When you are in the right directory, you do not need to give the full path of the sourcefile.

Example:

    cd ~/compilation/sources/filter
    javac -d ~/compilation/classes Toto.java

CLASSPATH

When a source file references a class, javac searches for the definition of that class using the class path. To specify the path javac uses to look up classes, use the -classpath path option.

Example:

    javac -classpath ~/compilation/classes -d ~/compilation/classes \
                  ~/compilation/sources/filter/Titi.java

creates a classfile Titi.class somewhere in the directory compilation/classes and looks up classes referenced in Titi.java in the directory compilation/classes. If you are too lazy to write the -classpath option all the time, you can also set the environment variable CLASSPATH to your classes directory. For tcsh this would look like this:

    setenv CLASSPATH ~/compilation/classes

For sh or bash:

    CLASSPATH=~/compilation/classes; export CLASSPATH

If you want to put more than one directory in your classpath, you can separate them by :

JAVA INTERPRETER

The java command executes Java programs. The path that java uses to look up the specified class and all other classes that it loads can be set by using the -classpath path option (if the classpath was not set already by the CLASSPATH variable).

Example:

    java -classpath ~/compilation/classes filter.Titi

runs the main() method of the Titi class. The interpreter looks for all the classes in the directory compilation/classes.

JLEX

JLex is itself a java program. First you need to install it by putting JLex.jar in ~/compilation/classes
Then run JLex from the interpreter:

Example:

    java -classpath ~/compilation/classes/JLex.jar JLex.Main \
                     ~/compilation/sources/filter/filter.lex
    mv ~/compilation/sources/filter/filter.lex.java \
                     ~/compilation/sources/filter/Scanner.java

These two comands leave a generated scanner in Scanner.java .

Probably you want to run these commands from the right directory:

Example:

    cd ~/compilation/sources/filter
    java -classpath ~/compilation/classes/JLex.jar JLex.Main filter.lex
    mv filter.lex.java Scanner.java

MAKE

Instead of typing these long commands repeatedly you might want to use Makefiles. You can put the following lines in a file ~/compilation/sources/filter/Makefile:

scanner:
<tab>java -classpath $(HOME)/compilation/classes/JLex.jar JLex.Main \
                 $(HOME)/compilation/sources/filter/filter.lex
<tab>mv $(HOME)/compilation/sources/filter/filter.lex.java \
                 $(HOME)/compilation/sources/filter/Scanner.java

Example:

    cd ~/compilation/sources/filter
    make scanner

now calls the two commands for you. You can have multiple paragraphs like the one above in a Makefile. Be sure really to use tabulators and not spaces to indent in a Makefile.

JAVACUP

As JLex, java_cup is itself a java program. First you need to install it by putting java_cup.jar in ~/compilation/classes
Then run java_cup from the interpreter:

Example:

    java -classpath ~/compilation/classes/java_cup.jar java_cup.Main \
             -package filter -parser Parser -symbols Tokens \
             -interface ~/compilation/sources/filter/filter.cup

This generates the parser in Parser.java and the token numbers in Tokens.java

DEBUGGER

If you are used to debug programs with a source-level debugger, then you should try out jdbg. It is used like java but you also have to provide the path to your sources, so that the debugger can find your sourcefiles.

Example:

    ~czenger/jdbg/bin/jdbg -classpath ~/compilation/classes \
            -sourcepath ~/compilation/sources filter.Titi

runs the main() method of the Titi class. The interpreter looks for all the classes in the directory compilation/classes.

Don't forget to read the javac documentation on the http://lampwww.epfl.ch/java/ pages.