Is that StringBuilder variable thread safe in this code?

Question

Consider the below struts Action class in which, I am using a StringBuilder variable inside the execute method. My question: Is the variable sb threadsafe or not?

public DemoAction extends Action
{
    ......

    public ActionForward execute(.....)
    {
       StringBuilder sb = new StringBuilder();
    }
}

What if the same variable sb declared outside the execute(). Remember there will be only one object for DemoAction in WebContainer.?

Answer 1

Local variables are thread safe, as long as no other thread somehow gets a reference to the same string builder instance, it’s thread safe.