public ObjVector<T> subVector(int begin, int end, int step) {
ObjVector<T> rlt = new ObjVector<T>();
for (int i = begin; i <= end; i += step) rlt.add(this.at(i));
return rlt;
}
public ObjVector<T> subVector(List<Integer> set) {
ObjVector<T> rlt = new ObjVector<T>();
for (Integer i : set) rlt.add(this.at(i));
return rlt;
}