Java tutorial
import java.util.HashMap; import java.util.Map; public class Main { public static void main(String[] args) { Map<Integer, String> map = new HashMap<>(); for (int i = 0; i < 10; i++) { map.putIfAbsent(i, "val" + i); } map.forEach((id, val) -> System.out.println(val)); map.remove(3, "val3"); System.out.println(map.get(3)); // val33 map.remove(3, "val33"); System.out.println(map.get(3)); // null } }