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Interfaces, Buttons and Event Handlers

Design Patterns

Patterns​

  • Patterns help us to identify ways in which a problem can be solved
    • Can identify the problem
    • Look at how people have solved this in the past
    • Much less 'thinking' and 'working out'
    • Avoid potential pitfalls later on
  • Usually many good ways to solve a problem

Layout managers​

  • Containers ask their layout manager to do the work
  • Container calls functions in the base class Layout Manager
  • Positioning of components
  • Key design pattern feature: the container has delegated some of its work to another class - the layout manager

Strategy Pattern​

  • This is a Behavioural Pattern
  • Allow objects behaviour to change at runtime
  • Strategies should be interchangeable
    • Should be same regardless of layout manager

(Sub-type) Polymorphism and Interfaces

  • Normally hide the data inside the class, and expose some kind of interface to the outside world
  • When using polymorphism to allow behaviour to be changed at runtime, don't care how it is implemented inside the class
  • Only care what functions/methods are available
  • An abstract method is a method without implementation

Summary​

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Interfaces​

  • If not have implementations for any of the methods, can use an interface instead of a class
  • Interface is a set of functions without implementations
    • Sub class MUST implement ALL functions (or be abstract)
  • Subclass implements interfaces but extends a class
  • Class can only extend one class
  • Can 'implement' many interfaces

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JButtons

  • Java Swing uses the Observer Pattern to monitor event handlers
  • Uses an interface, the ActionListener
    • An interface is just an abstract class which can use as a superclass

Observer Pattern​

  • Is a common pattern to use when we want to notify other objects that something has happened
    • Object to notify supports some interface (Observer)
    • Notifying object keeps a list/array/etc of there to notify
    • Notifying object considers these as the base class/interface and calls a method

JButton​

To handle key presses, JButton needs an object to tell