title: random generate character in a string
body: <p>i need to generate random character in a String java when user click on button.
  for example :if we take cat example i need to disply character in a string like follwing:</p>
  
  <p>CAT,ACT,TAC,TCA</p>
  
  <p>Thanks in advance</p>
  
  <p>Aswan</p>