[FIXED] Are instance variables of non-servlet classes are thread safe?

Issue

Are instance variables of non-servlet classes are thread safe if instantiated inside servlet method like below??

//Non-servlet Class
public class x{

  public String var1;
  public String var2;

  public String method(){
   return (var1 + var2);
  }
}

Servlet Class

public class myServlet extends HttpServlet {
   protected void doGet(HttpServletRequest request, HttpServletResponse response)
        throws ServletException, IOException {
      String varA = "Hello ";
      String varB = "World";
      String varC = null;
      x xx = new x();
      xx.var1 = varA;
      xx.var2 = varB;
      varC = xx.method();
   }
}

Solution

Are instance variables of non-servlet classes are thread safe?

In your case, it is not an instance variable but a locale variable in the execution scope of the doGet() method.

 protected void doGet(HttpServletRequest request, HttpServletResponse response)
        throws ServletException, IOException {
     ...
     x xx = new x();
     ...
    }

Locale variables declared and used in a method are isolated between the calls to it of multiple threads. So you have no potential concurrency here.

If you xx variable was a instance variable, you would have a race condition since multiple threads could access them in a concurrent way if the servlet was called multiple times in a close timing.

 public class myServlet extends HttpServlet {
     x xx = new x();
     ...
    protected void doGet(HttpServletRequest request, HttpServletResponse response)
        throws ServletException, IOException {
     ...
     xx.doSomething(); // concurrency race 
     xx.var1 = varA;   // concurrency race 
     ...
    }

Answered By - davidxxx