如果我有两个值相等的键，我如何返回设置种类（值 " - " 键，键）？

Question

只有当我有一对像名字（值）数字（键）这样的代码时，这段代码才有效，但我遇到了像名字数字、数字这样的情况。它返回名称number1，名称number2

 public Set<String> getAllContacts() {
        TreeSet<String> contacts = new TreeSet<>();
        if (phoneBook.isEmpty()) {
            return new TreeSet<>();
        } else {
            for (Map.Entry<String, String> entry : phoneBook.entrySet()) {
                contacts.add(entry.getValue() + " - " + entry.getKey());
            }
        }
        return contacts;
    }

Answer 1

基本上，你想要反转你的电话簿地图的键和值。根据您的示例，一个名称可以有多个编号s，因此输出结构应该是Map

Map<String, List<String>> phoneBookByName = new HashMap<>();
phoneBook.forEach((k, v) -> {
    List<String> numbers = phoneBookByName.computeIfAbsent(k, s -> new ArrayList<>());
    numbers.add(v);
});
TreeSet<String> contacts = new TreeSet<>();
phoneBookByName.forEach((k, v) -> contacts.add(k + " - " + String.join(", ", v)));
return contacts;

或者使用流

Map<String, List<String>> phoneBookByName = phoneBook.entrySet().stream()
    .collect(Collectors.groupingBy(Map.Entry::getValue, Collectors.mapping(Map.Entry::getKey, Collectors.toList())));
return phoneBookByName.entrySet().stream()
    .map(entry -> entry.getKey() + " - " + String.join(", ", entry.getValue()))
    .collect(Collectors.toCollection(TreeSet::new));