public ClassUseMapper(RootDoc root, ClassTree classtree) {
        this.classtree = classtree;

        // Map subclassing, subinterfacing implementing, ...
        for (Iterator<ClassDoc> it = classtree.baseclasses().iterator(); it.hasNext();) {
            subclasses(it.next());
        }
        for (Iterator<ClassDoc> it = classtree.baseinterfaces().iterator(); it.hasNext();) {
            // does subinterfacing as side-effect
            implementingClasses(it.next());
        }
        // Map methods, fields, constructors using a class.
        ClassDoc[] classes = root.classes();
        for (int i = 0; i < classes.length; i++) {
            PackageDoc pkg = classes[i].containingPackage();
            mapAnnotations(classToPackageAnnotations, pkg, pkg);
            ClassDoc cd = classes[i];
            mapTypeParameters(classToClassTypeParam, cd, cd);
            mapAnnotations(classToClassAnnotations, cd, cd);
            FieldDoc[] fields = cd.fields();
            for (int j = 0; j < fields.length; j++) {
                FieldDoc fd = fields[j];
                mapTypeParameters(classToFieldDocTypeParam, fd, fd);
                mapAnnotations(annotationToFieldDoc, fd, fd);
                if (! fd.type().isPrimitive()) {
                    add(classToField, fd.type().asClassDoc(), fd);
                }
            }
            ConstructorDoc[] cons = cd.constructors();
            for (int j = 0; j < cons.length; j++) {
                mapAnnotations(classToConstructorAnnotations, cons[j], cons[j]);
                mapExecutable(cons[j]);
            }
            MethodDoc[] meths = cd.methods();
            for (int j = 0; j < meths.length; j++) {
                MethodDoc md = meths[j];
                mapExecutable(md);
                mapTypeParameters(classToExecMemberDocTypeParam, md, md);
                mapAnnotations(classToExecMemberDocAnnotations, md, md);
                if (! (md.returnType().isPrimitive() || md.returnType() instanceof TypeVariable)) {
                    mapTypeParameters(classToExecMemberDocReturnTypeParam,
                        md.returnType(), md);
                    add(classToMethodReturn, md.returnType().asClassDoc(), md);
                }
            }
        }
    }