title: validate date in a particular format using preconditions
body: <p>I have a date in string format <code>YYYY/MM/DD HH:MM:SS</code> which I need to validate using preconditions google guava class. I am using <code>checkArgument</code> method in lot of other places. How can I use <code>checkArgument</code> method to validate <code>startDate</code> to make sure it is in this format only <code>YYYY/MM/DD HH:MM:SS</code> and if they are not, then throw IllegalArgumentException with some message.</p>
  
  <pre><code>public Builder startDate(String startDate) {
      // validate startDate here using checkArgument if it is not valid then throw IllegalArgumentException.
      this.sDate = startDate;
      return this;
  }
  </code></pre>
  
  <p>How can I use checkArgument method here?</p>