import java.util.*;

public class PriorityQueueDemo {

	public static void main(String[] args){

		PriorityQueue<String> stringQueue = new PriorityQueue<String>();
		
		stringQueue.add("ab");
		stringQueue.add("abcd");
		stringQueue.add("abc");
		stringQueue.add("a");
		
		
		Iterator<String> itr = stringQueue.iterator();
			while(itr.hasNext())
				System.out.println(itr.next());
		
		
		
	}
	}