Question

As I understand the doc, ParseDouble function made something like :

 Double parseDouble(String s) throws ... {       
      return new Double(Double.valueOf(s));
 }

Answer 1

The logic is the same, but the return value of Double.valueOf() return a heap allocated Double object, where as parseDouble returns a primitive double. Your code example is not quite correct. The java source reads:

public static double parseDouble(String s) throws NumberFormatException {
    return FloatingDecimal.readJavaFormatString(s).doubleValue();
}

public static Double valueOf(String s) throws NumberFormatException {
    return new Double(FloatingDecimal.readJavaFormatString(s).doubleValue());
}