Explain what the following code does?

Question

java.awt.EventQueue.invokeLater(new Runnable() {
    public void run() {
        new NewJFrame().setVisible(true);
    }
});

Please tell me what does the above code does actually. I am looking for line by line explanation. especially the first line and tell me why do we use that and in what scenarios we have to use this.

Answer 1

In this Example you see an anyonmous class that derives from Runnable. This anonymous class overrides the run method of the interface runnable. Then this anonymous class is instantiated and passed to the EventQueue.invokeLater method, which is a static method. This method appends the object into... well... the eventQueue. In the EvenQueue are many events, like keyboard events or mouse events or whatever. There is a Thread that continuesly polls data from this queue. Once that Thread reaches the anonymous class that was instantiated here, it will execute the run() method, which will instantiate an Object of class NewJFrame and set it to be visible.

The whole point of doing this this complicated is that the new JFrame().setVisible(true) part is not executed in the main thread, but in the event dispatching thread. In Swing you must execute all code that modifies the user interface in the event dispatching thread.