Method Double.valueOf(String s) where s should be string representation of floating-point value Floating value is described in spec is as follows

[Sign] Digits . [Digits] [ExponentPart] or
        [Sign] . Digits [ExponentPart]

Check out attached TestDouble.java should thow NumberFormatException.

---------------------8<--------------- TestDouble.java -----------------------
public class TestDouble {
  
  public static void main(String[] argv) {
    try {
       
      Double d = Double.valueOf("0");
      System.out.println("Failed Result:" + d.toString());
      d = Double.valueOf("1234");
      System.out.println("Failed Result:" + d.toString());
    }
    catch (Exception e) {
      System.out.println(e);
    }
  }
}