title: Java Date Time Start and End of day without any TimeZone information
body: <p>I have two strings as startDate and endDate. These have values like for example:</p>
  
  <pre><code>startDate="2019-09-29T06:00:00.000Z"
  endDate="2019-10-06T05:59:59.999Z"
  </code></pre>
  
  <p>Now let us say that these are in Mountain Time as the start of the day for startDate and End of the day for endDate. But as these are Strings, how can I make the program understand that these are can be converted to Mountain local time like:</p>
  
  <pre><code>startDate="2019-09-29T00:00:00.000Z"
  endDate="2019-10-05T11:59:59.999Z"
  </code></pre>
  
  <p>And the timezone is dynamic. I can get timestamp string from Eastern Time or any other timezone.<br>
  <strong>UPDATE</strong><br>
  I realized I should put in more information.<br>
  So the Moutain time I have put in is an example. It can be from Eastern Time or any other timezone. The only fact that this method knows is that startDate is the start of the day in some timezone and endDate is the end of the day in that timezone. I understand that 'Z' is the UTC time but finding out which timezone generated that UTC time at the start of the day (startDate) and end of the day(endDate) and converting back to the corresponding local time, is the challenge that I am facing.</p>