java - 如何获取 HashMap 的重复键值对？

Question

HashMap<Integer,Integer> hashmapsample= new HashMap<Integer, Integer>();

我可以有这样的值

(1 , 7)
(2 , 4)
(4 , 5)
(3,  7)

不会有任何重复的 Keys 。只能出现重复值

我想选择具有重复值的 (Key,Value) 对。

如果我将 Duplicate (Key,Value) 作为另一个 Hashmap 得到，那就太好了。我该怎么做。？

我期待输出

 (1 , 7)
 (3,  7)

Answer 1

这个怎么样？

public HashMap getDuplicateValues(HashMap in)
{
   // Clone input HashMap because we're removing stuff from it
   in = (HashMap)in.clone();
   HashMap rval = new HashMap();
   Object[] keys = in.keySet().toArray();

   // iterate through all keys
   for(int x=0;x<keys.length;x++) {
      Object value = in.get(keys[x]);
      in.remove(keys[x]);
      // if value is in input HashMap, store it in duplicate HashMap because it has another value
      if(in.containsValue(value)) {
         rval.put(keys[x],value);
      }
      // if value is in duplicate HashMap, store it also because it HAD another value earlier
      if(rval.containsValue(value)) {
         rval.put(keys[x],value);
      }
   }

   return(rval);
}

此方法将返回输入 HashMap 中所有重复值的键/值对。

---

测试代码:

  HashMap map = new HashMap();

  map.put("1","2");
  map.put("2","1");
  map.put("3","8");
  map.put("4","4");
  map.put("5","6");
  map.put("6","8");
  map.put("7","3");
  map.put("8","4");
  map.put("9","4");

  HashMap dups = getDuplicateValues(map);

  System.out.println("MAP = "+map);
  System.out.println("DUP = "+dups);

输出:

MAP = {3=8, 2=1, 1=2, 7=3, 6=8, 5=6, 4=4, 9=4, 8=4}
DUP = {3=8, 6=8, 4=4, 9=4, 8=4}