@Override
 public boolean isEmpty() {
   if (els.isEmpty() == true) {
     return true;
   }
   return false;
 }
 @Override
 public void clear() {
   els.clear();
 }
 @Override
 public void pop(Object element) {
   els.pop(element);
 }
 @Override
 public int length() {
   els.length();
   return 0;
 }
 @Override
 public void push(Object element) {
   els.push(element);
 }