title: Creating objects of Hashmap and assigning it to map reference. Why?
body: <p>Why we use,</p>
  
  <p>Map abc = new HashMap(20);</p>
  
  <p>instead of </p>
  
  <p>HashMap abc = new HashMap(20);</p>
  
  <p>please help me to find out the differnce between these two.</p>
  
  <p>would be grateful for help.</p>