call a java method using runtime.exec()

In my java code there is class A that has the following line:

Process localProcess = Runtime.getRuntime().exec(myString);

where myString is user supplied input and is passed to exec() at runtime.

Also there is a public method doSomething() in class A.

Can I somehow invoke doSomething() (through reflection, jdwp etc.) using exec() at runtime ?