Question

I’m trying to compile a Java project (of a Lisp interpreter) in Unix (Solaris to be specific). My problem is that I have a few classes that extend other classes, but when javac attempts to compile the extended classes, it says it can’t find the superclass.

Commands I type:

javac -g LispObject.java
javac -g Sexp.java

The first one works fine; but the second halts with the following error:

Sexp.java:7: Superclass interpreter.LispObject of class interpreter.Sexp not found.
public class Sexp extends LispObject
                          ^
1 error

(I don’t know if it’s very relevant but this is for a class project so I have to use a makefile for the compilation, so I can’t use any IDEs for the compilation… which sucks because everything worked fine in NetBeans.)

Code for LispObject.java:

package interpreter;

public class LispObject extends java.lang.Object
{
   // empty
}

Code for Sexp.java:

package interpreter;

public class Sexp extends LispObject
{
   // body stuff goes here
}

Answer 1

Try adding -cp . to your javac calls so that it searches the current directory for already compiled classes. Second call would be:

javac -cp . -g Sexp.java

Alternatively, give it all your .java files in one go:

javac -g LispObject.java Sexp.java

Generally the best would be to set up a specific build directory (i’ll call it /some/dir/build) and use:

javac -cp /some/dir/build -d /some/dir/build your_file.java

so that the .class files don’t come polluting your source file directorie(s).

Keep in mind that you should keep your directory structure in sync with your package hierarchy. If your classes are in the interpreter package, they should be placed in a directory with that name.

So in this specific instance, your compile command should look like:

javac -cp /some/dir/build -d /some/dir/build interpreter/LispObject.java
javac -cp /some/dir/build -d /some/dir/build interpreter/Sexp.java