Error when assigning value to a Double in Java Servlet

Question

Hi,

I was debugging an error I was getting with a java servlet. I was assigning a value to a Double in the class, however occasionally when I ran the servlet I was getting a random number as the value. Not sure if this has to do with using the wrapper versus primitive?

Here is a snippet of code:

---

public class MyClass extends HttpServlet {

      private Double MinCost = 10000000.0;

      public void doPost(HttpServletRequest req, HttpServletResponse resp)
            throws IOException { 

// rest of code here ----

---

When I run the servlet, I sometimes get the value of MinCost to be some other number, and sometimes it is correct.

I have changed the code to just declare the variable MinCost but not assign it a value, and assign it a value later on in my doPost method.

Any explanation as to why this happens?

Thanks

Answer 1

My guess is that this is happening because of previous requests. Don't forget that the same servlet instance is used for multiple requests - are you expecting the value to be 10000000.0 at the start of each request? That's not how servlets work. If you want state within an object - and new state at the start of each request - you'll have to put that state into a separate class, and create an instance of the class in doGet/doPost/service etc.