How do I keep the iteration order of a List when using Collections.toMap() on a stream?

Question

I am creating a Map from a List as follows:

List strings = Arrays.asList(\"a\", \"bb\", \"ccc\");

Map

        

Answer 1

Provide your own Supplier, Accumulator and Combiner:

    List myList = Arrays.asList("a", "bb", "ccc"); 
    // or since java 9 List.of("a", "bb", "ccc");
    
    LinkedHashMap mapInOrder = myList
        .stream()
        .collect(
            LinkedHashMap::new,                                   // Supplier
            (map, item) -> map.put(item, item.length()),          // Accumulator
            Map::putAll);                                         // Combiner

    System.out.println(mapInOrder);  // {a=1, bb=2, ccc=3}