Converting a String to a double requires that you first convert the String to a Double object, then convert the Double object to a double data type (Double is an object, while double is a primitive data type).

public class s2d {

   public static void main (String[] args) {

      // String s = "fred";    // do this if you want an exception

      String s = "100.00";

      try {
         double d = Double.valueOf(s.trim()).doubleValue();
         System.out.println("double d = " + d);
      } catch (NumberFormatException nfe) {
         System.out.println("NumberFormatException: " + nfe.getMessage());
      }

   }

}

Other notes

• Double.toString(double d) is used to convert in the other direction, from a double to a String.