Does event sources are registered with only one object of a listener? No new listener's object is created every time when a user clicks a button.
This program appends the string with a new incremented character when user clicks on the button.
'build' is the instance variable of the listener class. 'build' remembers its previous value and appends the new value when user clicks the button that means no new listener object is created. Only the function actionPerformed() is invoked on the same object..