What does a block of code do after a new operation in Java?

Question

SwingUtilities.invokeLater(new Runnable() {
    public void run() {
        Example ex = new Example();
        ex.setVisible(true);
    }
});

Here a block of code follows new Runnable(). How do I understand this code? I don't remember we can pass a code block directly to any object in java.

Answer 1

It is not a code block. It is an object.

When you say,

new Runnable()

you are creating an object that implements the Runnable interface, specifically the run() method.

As the method name suggests, invokeLater() will invoke the run() method of your runnable interface implementation object (or Runnable object) at some later point in time.

As another poster mentioned, this is an example of Anonymous Classes. It is really a convenience mechanism to quickly write code in a more concise fashion. If you don't like this, you can do it this way -

Create a new class that implements Runnable -

public class RunnableImplementation implements Runnable
 {
   public void run() 
    {
        Example ex = new Example();
        ex.setVisible(true);
    }
 }

Then, the code in your example becomes -

SwingUtilities.invokeLater(new RunnableImplementation()); 

Answer 2

It's creating an instance of an anonymous inner class. Rather than deriving a named class from Runnable and creating an instance of it, you can do the whole thing inline.

See Anonymous Classes.