Avoid creating a stacktrace prior to JDK 1.7

Dear All,

I have the following code deep down in a
recursion which eats up a lot of stack.
The recursion is not shown but only
the code:

     Class<?> class;
     try {
         class = Class.forName(str);
     } catch (ClassNotFoundException x) {
         class = null;
     }

Will it every time I call it for a
non-existing class build the whole stack
trace for the exception x and then
immediately forget about it?

Now I see in JDK 1.7 (*) a protected
constructor:

    package java.lang;

    protected Throwable(String message,
          Throwable cause,
          boolean enableSuppression,
          boolean writableStackTrace)

If I were to write my own forName()
method I would set the writableStackTrace
to false if the exception is only needed
to immediately notify the callee about
something.

But what if I have JDK 1.6 only available
and not JDK 1.7. Can I instruct an exception
to not fill the stack trace? And way
arround?

Bye

(*)
http://download.oracle.com/javase/7/docs/api/