Question

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

I can have values like

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

There wont be any duplicate Keys . Only Duplicate values can occur

I want to pick the (Key,Value) pair which has duplicate values.

If I get the Duplicate (Key,Value) as another Hashmap it would be great.
How Do I go about it.?

I expect the output

 (1 , 7)
 (3,  7)

Answer 1

How about this?

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);
}

This method will return key/value pairs for all the duplicate values in the input HashMap.

---

Test code:

  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);

Output:

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}