Implementing MVC in Java And Various Other Random Topics

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Implementing MVC in Java(And Various Other
Random Topics)
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Plan

• Quick rehash of MVC
• How to implement MVC in Java
• Brief introduction to Timers (something youll
  need)
• A new GUI component
• Develop a small Java system using MVC with
  striking parallels to your project

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MVC Rehash Model

• maintains state information with methods to
  access and modify that state
• independent (mostly) of the view and controller
• we can do things to the model, but the model
  doesnt move itself
• think of the model as a poseable action figure or
  a lump of clay
• in a board game the game board, playing pieces,
  etc. are parts of the model

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MVC Rehash View

• displays the state of the model in some way
• should only access the state of the modelit
  should not modify it

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MVC Rehash Controller

• what actually makes things happen
• in a graphical Java program, this is usually made
  up of Listeners
• in theory, a completely separate module from the
  model and views. in practice, the controller may
  be spread out a little and there may be some
  overlap (some listeners may be in the view class).

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MVC Example Clock

• model stores a time and has a way to get and set
  that time
• views analog and digital displays
• controller(s) us (we can wind the hands), the
  gears (or whatever) that change the time

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MVC In Java Observer/Observable

• model class extends java.util.Observable
• view classes implement java.util.Observer
  interface
• Observers get notified when the things they are
  observing are changed (so your view can update
  itself)

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MVC In Java Observable

• class java.util.Observable
• public void addObserver(Observer o)
• public void deleteObserver(Observer o)
• public void deleteObservers()
• public void notifyObservers()
• public void notifyObservers(Object arg)
• protected void setChanged()

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MVC In Java Observer

• interface java.util.Observer
• void update(Observable o, Object arg)

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Random change of topic Timers

• Motivation
• how do we animate things on the screen?
• how do we control the flow of a game?

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Timers

• class javax.swing.Timer
• Timer(int delay, ActionListener al)
• public void start()
• public void stop()
• warning there is also a java.util.Timer. this
  can cause problems if you are importing
  javax.swing. and java.util. in the same file.

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Timers example

• import javax.swing. import java.awt.event.
• public class TimerExample
• public static void main(String args)
• new JFrame().show() // just to keep the
  program alive
• Timer tim new Timer(1000, new
  ActionListener()
• public void actionPerformed(ActionEvent
  event)
• JOptionPane.showConfirmDialog(null,
• "Are we there yet?", "Title",
• JOptionPane.YES_NO_OPTION,
• JOptionPane.QUESTION_MESSAGE)
• )
• tim.start()

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A new Component JComboBox

• JComboBox()
• JComboBox(Vector items)
• JComboBox(ComboBoxModel model)Constructs a combo
  box. Can optionally pass a vector or model of
  items. (See DefaultComboBoxModel for a model
  implementation.)
• addActionListener(ActionListener al)Causes an
  action event to be sent to listener al when the
  user selects or types a new item in the combo
  box.

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Methods for Managing Items

• addItem(Object item)
• Object getItemAt(int index)
• removeAllItems()
• removeItem(Object item)
• removeItemAt(int index)
• note add and remove are the inherited methods
  from Componentdont confuse them with addItem
  and removeItem

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Methods for the Selected Item

• int getSelectedIndex()
• Object getSelectedItem()
• setSelectedItem(Object item)
• setSelectedIndex(int index)
• setEnabled(boolean enabled)
• setEditable(boolean editable)If editable, the
  user can type new arbitrary values into the combo
  box.

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Additional Information

• Java Tutorial
• http//java.sun.com/docs/books/tutorial/
• Java Tutorial Timers
• http//java.sun.com/docs/books/tutorial/uiswing/mi
  sc/timer.html
• Java Tutorial Visual Index of Components
• http//java.sun.com/docs/books/tutorial/uiswing/co
  mponents/
• components.html