import java.util.List;
import java.util.Map;
import java.util.Set;

// List.ofLazy, Map.ofLazy (JDK 26 and 27) and Set.ofLazy (new in JDK 27): each element is computed on first access.
public class LazyCollections {
    public static void main(String[] args) {
        List<String> list = List.ofLazy(3, i -> { System.out.println("  computing list element " + i); return "v" + i; });
        System.out.println("list created, size " + list.size() + " (nothing computed yet)");
        System.out.println("list.get(1) = " + list.get(1));
        System.out.println("list.get(1) again = " + list.get(1));

        Map<String, Integer> map = Map.ofLazy(Set.of("a", "bb", "ccc"), k -> { System.out.println("  computing map value for " + k); return k.length(); });
        System.out.println("map created, size " + map.size() + " (nothing computed yet)");
        System.out.println("map.get(\"bb\") = " + map.get("bb"));
        System.out.println("map.get(\"bb\") again = " + map.get("bb"));

        Set<Integer> set = Set.ofLazy(Set.of(1, 2, 3), n -> { System.out.println("  testing " + n); return n > 1; });
        System.out.println("set created");
        System.out.println("set.contains(2) = " + set.contains(2));
        System.out.println("set.contains(1) = " + set.contains(1));
        System.out.println("set.contains(9) = " + set.contains(9));
        System.out.println("set.size() = " + set.size());
    }
}