java - 当您更新一个集合(即映射中的值)，然后将键和值放入映射中时，是否会创建重复项？

Question

例如，我有这样的代码:

public void addDocument(DocumentId documentId, Reader reader) throws IOException {
        String s = "";
        List<String> list;
        BufferedReader br = new BufferedReader(reader);
        while((s=br.readLine())!=null)
        {
            list = Arrays.asList(s.toLowerCase().split("\\W+"));
            for(int i = 0; i < list.size(); i++)
            {
                if(!map.containsKey(list.get(i)))
                {
                    Set<DocumentId> newset = new HashSet<>();
                    newset.add(documentId);
                    map.put(list.get(i), newset);
                }
                else
                {
                    Set<DocumentId> set = map.get(list.get(i));
                    set.add(documentId);
                    map.put(list.get(i), set);
                }
            }
        }

    }

是map.put(list.get(i), set);在映射中创建键和值的副本？如果是这样，我应该在再次添加更新的列表之前删除该对吗？

附注 map 是Map<String, Set<DocumentId>>

Answer 1

Map不允许重复key，Map内部的key会替换旧值，可以查看API here :

Associates the specified value with the specified key in this map (optional operation). If the map previously contained a mapping for the key, the old value is replaced by the specified value. (A map m is said to contain a mapping for a key k if and only if m.containsKey(k) would return true.)