title: How to declare final HashMap that should not allow to update or remove element
body: <p>I have a hash map like,</p>
  
  <pre><code>public static void main(String[] args) {
      final Map&lt;String, String&gt; daysMap = new HashMap(7);
      daysMap.put("1", "Sunday");
      daysMap.put("2", "Monday");
      daysMap.put("3", "Tuesday");
      daysMap.put("4", "Wednesday");
      daysMap.put("5", "Thursday");
      daysMap.put("6", "Friday");
      daysMap.put("7", "Saturday");
  }
  </code></pre>
  
  <p>In this map <br/>
  1. Should not allow to put more than 7 elements <br/>
  2. Should not update value for corresponding key [like daysMap.put("5", "xxx");]<br/>
  3. Should not allow to remove any key</p>
  
  <p>How to do?</p>