What is "val$title" (dollar sign in expression) in Java?

Question

private void launchEventPanel(String title) {
    EventQueue.invokeLater(new Runnable(title) {
        public void run() {
            JFrame myFrame = new JFrame();
            myFrame.setTitle(this.val$title);
            myFrame.setIconImage(CrConference.this.mainCore.myPanel.myIconManager.getPromptIcon(Mart.class.toString()));
            myFrame.getContentPane().add(Conference.this.myEventPanel, "Center");
            myFrame.pack();
            myFrame.setVisible(true);
        }
    });
}

i got some code that i am trying to compile and understand. help highly appreciated

Answer 1

As described here and here, the argument to the Runnable constuctor and "this.val$" to the field name is added by the compiler and shows up in the generated bytecode. Hence these extra things are reflected in the decompiled code.

To get the original decompiled code, add final to the declaration of title and remove title from the call to Runnable and the this.val$ from in front of title:

private void launchEventPanel(final String title) {
    EventQueue.invokeLater(new Runnable() {
        public void run() {
            JFrame myFrame = new JFrame();
            myFrame.setTitle(title);
            myFrame.setIconImage(CrConference.this.mainCore.myPanel.myIconManager.getPromptIcon(Mart.class.toString()));
            myFrame.getContentPane().add(Conference.this.myEventPanel, "Center");
            myFrame.pack();
            myFrame.setVisible(true);
        }
    });
}