public class QueryQueue { HashSet queries; int size; public QueryQueue() { queries = new HashSet(); size = 0; } public LocalQuery pop() { if (queries.isEmpty()) return null; LocalQuery q = (LocalQuery) queries.iterator().next(); queries.remove(q); size--; return q; } public void push(LocalQuery x) { queries.add(x); size++; } public int size() { return size; } public boolean isEmpty() { if (size == 0) return true; else return false; } }