如果我有两个值相等的键，我如何返回一个 Set<string> 有点（值+“-”+键“，”+键）？</string>

Question

This code works only when I have a pair like name(value) + number(key), but I'm stuck with situation like - name + number, number. It returns name + number1, name + 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

Basically you want to invert key and value of your phoneBook map. Since one name can have multiple number s according to your example the output structure should be Map<String, List<String>> . With this name oriented phone book you can easily create your contact collection. Eg

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;

or using streams

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));