java - 使用附加值或新值扩展 ImmutableMap

Question

很像 ImmutableList 可以这样扩展:

ImmutableList<Long> originalList = ImmutableList.of(1, 2, 3);
ImmutableList<Long> extendedList = Iterables.concat(originalList, ImmutableList.of(4, 5));

如果我有一个现有 map ，我该如何扩展它(或创建一个具有替换值的新副本)？

ImmutableMap<String, Long> oldPrices = ImmutableMap.of("banana", 4, "apple", 7);
ImmutableMap<String, Long> newPrices = … // Increase apple prices, leave others.
                                         //  => { "banana": 4, "apple": 9 }

(我们不要寻求有效的解决方案，显然是 that doesn't exist by design 。这个问题而是寻求最惯用的解决方案。)

Answer 1

您可以明确地创建一个构建器:

ImmutableMap<String, Long> oldPrices = ImmutableMap.of("banana", 4, "apple", 7);
ImmutableMap<String, Long> newPrices =
    new ImmutableMap.Builder()
    .putAll(oldPrices)
    .put("orange", 9)
    .build();

编辑:
如评论中所述，这将不允许覆盖现有值。这可以通过遍历不同 Map(例如，HashMap)的初始化程序 block 来完成。它一点也不优雅，但它应该可以工作:

ImmutableMap<String, Long> oldPrices = ImmutableMap.of("banana", 4, "apple", 7);
ImmutableMap<String, Long> newPrices =
    new ImmutableMap.Builder()
    .putAll(new HashMap<>() {{
        putAll(oldPrices);
        put("orange", 9); // new value
        put("apple", 12); // override an old value
     }})
    .build();