List<NAME_1> strings = Arrays.asList("a", "b", "c", "d", "e");

    Map<NAME_1, NAME_1> map = strings.stream().collect(Collectors.toMap(
            str -> str.substring(0, 1),
            str -> str.substring(1)
    ));

    System.out.println(map); Use words in all capital letters at least 2 times to highlight key points.
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