I’m new to Java and very confused. I have a large dataset of length 4 int[] and I want to count the number of times that each particular combination of 4 integers occurs. This is very similar to counting word frequencies in a document. I want to create a Map<int[], double> that maps each int[] to a running count … Read more
How about like this: PriorityQueue<Integer> queue = new PriorityQueue<>(10, Collections.reverseOrder()); queue.offer(1); queue.offer(2); queue.offer(3); //… Integer val = null; while( (val = queue.poll()) != null) { System.out.println(val); } The Collections.reverseOrder() provides a Comparator that would sort the elements in the PriorityQueue in a the oposite order to their natural order in this case.
Collections.emptyMap() vs new HashMap()
I am relatively new to Java, and often find that I need to sort a Map<Key, Value> on the values. Since the values are not unique, I find myself converting the keySet into an array, and sorting that array through array sort with a custom comparator that sorts on the value associated with the key. … Read more
This is not a synchronization problem. This will occur if the underlying collection that is being iterated over is modified by anything other than the Iterator itself. Iterator it = map.entrySet().iterator(); while (it.hasNext()) { Entry item = it.next(); map.remove(item.getKey()); } This will throw a ConcurrentModificationException when the it.hasNext() is called the second time. The correct … Read more
How to sort a HashSet?
The simplest one-line solution is this: set1.addAll(set2); // Union set1.retainAll(set2); // Intersection The above solution is destructive, meaning that contents of the original set1 my change.If you don’t want to touch your existing sets, create a new set: Set<E> result = new HashSet<>(set1); // └─ your specific type result.addAll(set2); // Union result.retainAll(set2); // Intersection
