Assumed final?

I always thought the code below would have generated a error on compile
that frame wasn't final. But I see when I compile it now with JDK 8
that there is no error unless I make another assignment to frame. If I
uncomment the frame = null; statement, then I get the error;

C:\Users\Knute Johnson>javac test9.java
test9.java:17: error: local variables referenced from an inner class
must be final or effectively final
                         frame.dispose();
                         ^
1 error

So it appears that the Java 8 compiler has gotten smarter or I haven't
been paying enough attention :-).

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;

public class test9 extends JPanel {
     public test9() {
         setPreferredSize(new Dimension(320,180));
         setBackground(Color.BLUE);
     }

     public static void main(String... args) {
         EventQueue.invokeLater(new Runnable() {
             public void run() {
                 JFrame frame = new JFrame("test9");
                 frame.addWindowListener(new WindowAdapter() {
                     public void windowClosing(WindowEvent we) {
                         frame.dispose();
                     }
                 });
                 frame.add(new test9(),BorderLayout.CENTER);
                 frame.pack();
                 frame.setVisible(true);

                 //frame = null;
             }
         });
     }
}

--

Knute Johnson