According to http://docs.oracle.com/javase/8/docs/technotes/tools/windows/javadoc.html#CHDGAHAJ:
"If you want to search for source and class files in separate paths, then use both -sourcepath and -classpath. For example, if you want to document com.mypackage, whose source files reside in the directory \user\src\com\mypackage, and if this package relies on a library in , \user\lib, then you would use the following command:
javadoc -sourcepath \user\lib -classpath \user\src com.mypackage"

The handlers of both options just overwrite the same "sourcepath" variable so this definitely cannot work as described above:
..................
            new Hidden(this, "classpath", 1) {
                @Override
                public boolean process(String opt, ListIterator<String> args) {
                    if (sourcepath.length() == 0) {
                        optionsProcessed.add(this);
                        sourcepath = args.next();
                    }
                    return true;
                }
            },
..................
            new Hidden(this, "sourcepath", 1) {
                @Override
                public boolean process(String opt, ListIterator<String> args) {
                    optionsProcessed.add(this);
                    sourcepath = args.next();
                    return true;
                }
            }
..................