is there any api to get only parts which are present in part structure

Hello,

I tried with the given solution. it is showing the type cast exception. 

Image is attached

This is the code i am using.

wt.query.QuerySpec qs = new wt.query.QuerySpec(NavigationCriteria.class);
qs.appendWhere(new SearchCondition(NavigationCriteria.class, NavigationCriteria.SHARED_TO_ALL,
SearchCondition.IS_FALSE), new int[] { 0 });
qs.appendAnd();
qs.appendWhere(new SearchCondition(NavigationCriteria.class, NavigationCriteria.NAME, SearchCondition.EQUAL,
"Test"), new int[] { 0 });
QueryResult qr = PersistenceHelper.manager.find(qs);
System.out.println("Size ************************* " + qr.size());

NavigationCriteria nav = null;
while (qr.hasMoreElements()) {
nav = (NavigationCriteria) qr.nextElement();

System.out.println("Name of NAvigation criteria " + nav.getIdentity() + ",T " + nav.getType() + ",N "
+ nav.getName() + ", A " + nav.getApplicationName());
}

QueryResult pp = wt.part.WTPartHelper.service.getUsesWTParts(part, nav);
System.out.println("PP Size " + pp.size());
while (pp.hasMoreElements()) {
Persistable obj = (Persistable) pp.nextElement();
WTPart pt = (WTPart) obj;

}