title: Find duplicate values in Java Map?
body: <p>I want to display the values in a <code>HashMap</code>. A <code>HashMap</code> may have duplicate values (but not duplicate keys), but I want to display a value only once. </p>
  
  <p>So I should find whether the <code>Map</code> has duplicate values. I know we can iterate over the <code>Map</code> and use the return boolean of <code>map.containsValue(value)</code>. I want to know whether any method exists to find duplicate values in map or we should I write code myself?  </p>