Objects must implement java.lang.Comparable<T> (Exception: cannot be cast to java.lang.Comparable)
Ordered collection (java.lang.Comparable<T>)
null elements not allowed
Duplicates elements allowed

PriorityQueue<String> pq = new PriorityQueue<>(); // pq.add(null); // java.lang.NullPointerException pq.add("c"); pq.add("bb"); pq.add("bb"); pq.add("aaa"); pq.add("aaa"); pq.add("aaa"); while (!pq.isEmpty()) System.out.println(pq.remove()); // pq.forEach(System.out::println); // elements of the queue might be printed in a random order
Output: aaa aaa aaa bb bb c

PriorityQueue<String> pq = new PriorityQueue<>(Comparator.comparing(String::length)); // pq.add(null); // java.lang.NullPointerException pq.add("c"); pq.add("bb"); pq.add("bb"); pq.add("aaa"); pq.add("aaa"); pq.add("aaa"); while (!pq.isEmpty()) System.out.println(pq.remove()); // pq.forEach(System.out::println); // elements of the queue might be printed in a random order
Output: c bb bb aaa aaa aaa