In this article, I will list some useful techniques that can be used in our daily life as a developer.
Convert PriorityQueue to Array
PriorityQueue<int[]> pq = new PriorityQueue<>();
int[][] result = pq.toArray(new int[pq.size()][2]);
Convert integer array to list
Method 1
IntStream.of(arr).boxed().collect(Collectors.toList())
Method 2
Arrays.stream(stones).boxed().collect(Collectors.toList())
Convert string array to list
String[] strs = new String[]{"a", "b", "c"};
Arrays.stream(strs).collect(Collectors.toList())
Using Comparator.comparingInt()
Say we have a priority queue in Java with List<Integer> as element, we would like to sort the priority queue based on the first element:
Queue<List<Integer>> pq = new PriorityQueue<>(Comparator.comparingInt(k -> k.get(0)));
Join List of String into a single String
List<String> list = Arrays.asList("Hello", "world");
String result = list.stream().collect(Collectors.joining(" ")); // result: "Hello world"
Add Map entries with value initialization
Map<String, List<String>> map = new HashMap<>();
map.computeIfAbsent(key, k -> new ArrayList<>()).add(value);
Get sum of an array
int[] array = {1, 2, 3, 4};
int sum = Arrays.stream(array).sum();