title: Sonar - Make DATE_FORMAT as instance variable
body: <p>I have a rest web service, and below is how i have declared DateFormat as this is the date format i am going to use application wide. </p>
  
  <p>When i did code analysis using SonarLint eclipse plug-in, i got major warning saying "Make <strong>DATE_FORMAT</strong> as instance variable."</p>
  
  <pre><code>public class Constants {
  
      private Constants() {
  
      }
  
      public static final DateFormat DATE_TIME_FORMAT = new SimpleDateFormat("yyyy-MM-dd'T'HH:mm:ss:SSS");
  
  }
  </code></pre>
  
  <p>Can anyone tell me what issue i might face if i use it this way in my rest API ? <br>If i use it as instance variable i will end up declaring it in multiple classes ?</p>