title: Regular Expression - inserting space after comma only if succeeded by a letter or number
body: <p>In Java I want to insert a space after a String but only if the character after the comma is succeeded by a digit or letter.    I am hoping to use the replaceAll method which uses regular expressions as a parameter.  So far I have the following:</p>
  
  <pre><code>String s1="428.0,chf";
  s1 = s1.replaceAll(",(\\d|\\w)",", ");   
  </code></pre>
  
  <p>This code does successfully distinguish between the String above and one where there is already a space after the comma.   My problem is that I can't figure out how to write the expression so that the space is inserted.   The code above will replace the c in the String shown above with a space.    This is not what I want.   </p>
  
  <p><code>s1</code> should look like this after executing the <code>replaceAll</code>: <code>"428.0 chf"</code></p>