java access class's variable in thread and use outside thread

Question

I've a GUI Class Named as NewFrame.java and another one is Client.java . in Client.java, the NewFrame's object is made inside a thread. ex,

public class ClientA {

NewJFrame gui;
int x ;

public void go() {
            java.awt.EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                gui  = new NewJFrame();
                gui.setVisible(true);
                x = 10;
            }
        });

        System.out.println(x); // does not print 10 but it prints 0

        gui.setTextboxvalue("value changed !!!"); 

        // can'se pass value to the function, with this error occurs as,
        // "java.lang.NullPointerException" at here.

      }
}

here two problems occuring, there is the setter method in NewFrame class named setTextboxValue but calling this as shown above the error occurs "java.lang.NullPointerException".

another problem is : why i can't set the variable x inside that thread, setting this inside thread, the outside printing the variable x 's value which is 10 is not printing there instead it prints 0

Answer 1

EventQueue.invokeLater invokes its methods on a separate thread, which is fired off asynchronously on the event dispatch thread after all the other tasks on the event dispatch thread have finished. In other words, that code inside the run() method is likely going to be executed after your method finishes. Therefore, the gui variable is still going to be null, resulting in a NullPointerException when you call gui.setTextboxvalue ; and x is still going to be 0 when you print out the value.