title: When is the unmodifiablemap (really) necessary?
body: <p>I have a map of constants, like this:</p>
  
  <pre><code>private static Map&lt;String, Character&gt; _typesMap =
          new HashMap&lt;String, Character&gt;() {
          {
              put ("string", 'S');
              put ("normalizedString", 'N');
              put ("token", 'T');
              // (...)
          }
  </code></pre>
  
  <p>Do I really need to use <code>Collections.unmodifiableMap()</code> to create this map? What is the advantage of using it? Are there any disadvantages of not using it, besides the obvious fact that they are not really becoming constant?</p>