Holder.java

class Holder implements Verzameling {
    private ArrayList<Object> l = new ArrayList<Object>();
    public void add(Object o) {l.add(o);}

    @Override
    public Iterator maakIterator(String type) {
        /*
        if (type.equals("Seq")) return new Seq();
        else if (type.equals("Cyc")) return new Cyc();
        else return null;
        */
        // or
        switch(type) {
            case "Seq":
                return new Seq();
            case "Cyc":
                return new Cyc();
            default:
                return null;
        }
    }

    private class Seq implements Iterator {
        private int i = 0;
        @Override
        public Object next() {
            if (i < l.size()) return l.get(i++);
            else return null;
        }

    }

    private class Cyc implements Iterator {
        private int i = 0;
        @Override
        public Object next() {
            if (i >= l.size()) {
                i = 0;
                return l.get(i++);
            }
            else return l.get(i++);
        }

    }

}