This full Java constructors tutorial quickly provides a deep understanding of this important programming concept. What is a constructor in Java? A Java constructor is a special method that lets ...

In this example (from an Oracle tutorial) the ActionListener added to the button is defined in an anonymous inner class with an actionPerformed method instead of using a separate named class.

More about Java interfaces For an introduction to Java interfaces, including the difference between classes and interfaces, see my Java 101 tutorial Working with interfaces in Java.