Design Patterns and Best Practices in Java

Observer

The observer pattern got replaced in Java 8 with lambda expressions. The most obvious example is the ActionListener replacement. The old code, using anonymous class listeners, got replaced with a simple function call:

JButton button = new Jbutton("Click Here");button.addActionListener(new ActionListener() {   public void actionPerformed(ActionEvent e)   {    System.out.println("Handled by the old listener");  }});

The new code is just one line:

button.addActionListener(e -> System.out.println("Handled by lambda"));