class FilteredProjectDependencyGraph implements ProjectDependencyGraph {

    private ProjectDependencyGraph projectDependencyGraph;

    private Map<MavenProject, ?> whiteList;

    private List<MavenProject> sortedProjects;

    /**
     * Creates a new project dependency graph from the specified graph.
     *
     * @param projectDependencyGraph The project dependency graph to create a sub view from, must not be {@code null}.
     * @param whiteList The projects on which the dependency view should focus, must not be {@code null}.
     */
    FilteredProjectDependencyGraph(
            ProjectDependencyGraph projectDependencyGraph, Collection<? extends MavenProject> whiteList) {
        this.projectDependencyGraph =
                Objects.requireNonNull(projectDependencyGraph, "projectDependencyGraph cannot be null");

        this.whiteList = new IdentityHashMap<>();

        for (MavenProject project : whiteList) {
            this.whiteList.put(project, null);
        }
    }

    /**
     * @since 3.5.0
     */
    public List<MavenProject> getAllProjects() {
        return this.projectDependencyGraph.getAllProjects();
    }

    public List<MavenProject> getSortedProjects() {<FILL_FUNCTION_BODY>}

    public List<MavenProject> getDownstreamProjects(MavenProject project, boolean transitive) {
        return applyFilter(projectDependencyGraph.getDownstreamProjects(project, transitive));
    }

    public List<MavenProject> getUpstreamProjects(MavenProject project, boolean transitive) {
        return applyFilter(projectDependencyGraph.getUpstreamProjects(project, transitive));
    }

    private List<MavenProject> applyFilter(Collection<? extends MavenProject> projects) {
        List<MavenProject> filtered = new ArrayList<>(projects.size());

        for (MavenProject project : projects) {
            if (whiteList.containsKey(project)) {
                filtered.add(project);
            }
        }

        return filtered;
    }

    @Override
    public String toString() {
        return getSortedProjects().toString();
    }
}

        if (sortedProjects == null) {
            sortedProjects = applyFilter(projectDependencyGraph.getSortedProjects());
        }

        return new ArrayList<>(sortedProjects);
    
<no_super_class>