title: Check if string is number in android
body: <p>I have three text fields all which are numbers or a decimal number.</p>
  
  <p>They are accepted as strings which are later converted.</p>
  
  <p>However, i want to validate these fields so that only the numbers or decimal numbers are accepted. </p>
  
  <p>Whats the easiest way to ensure that these fields are only characters 0-9. </p>
  
  <p>I would prefer an if statement but any solution would be nice!</p>