GUIs in the Java MiniProject

1
GUIs in the Java Mini-Project

• Imperial Oil Summer Institute for Computer
  Studies Educators
• August 2006.

2
The Model/View/Controller Paradigm

• Separate the application logic (model) from the
  UI (view)
• The view handles all interactions with the user
• The model keeps track of the state of the
  application
• The view knows everything about the model
• Contains a reference to the model object
• Implements the IView interface
• Automatically adds itself to the list of views in
  the model
• The model only knows that there may be some views
  looking at it
• Whenever something significant changes in the
  state of the game, call the updateAllViews()
  method

3
What is an Interface?

• An interface defines a set of methods
• It is like defining a data type
• No instance variables, no constructor
• It will be implemented by a class
• It is a contract by the class to implement all
  methods declared within the interface
• The class may implement more methods beyond those
  defined in the interface
• It may be used to simulate multiple inheritance
• Examples
• IView
• Implemented by all GUI elements viewing the model
• ActionListener
• Implemented by inner classes defining listeners
  within the GUI

4
MVC in the Java Mini-Project

• Model - Library.java
• in the mini-project, the state is recorded in the
  queryResult instance variable
• View - LibraryGUI.java
• updateView() displays the value of queryResult
  in the text area
• Controller - MiniProjectMain.java
• Weak coupling (optional)
• limited method interactions between the model and
  the model and the view
• the model only calls the updateView() method
• the view only calls the doCommand() method

5
Creating a GUI

• Import Java libraries -
• javax.swing., java.awt., java.awt.event.,
• Construct a frame object
• Construct a model object
• Construct a JPanel object with the model as a
  parameter
• Declare components
• Instance variables
• Choose, construct and set the layout
• Examples FlowLayout, GridLayout, BorderLayout,
  BoxLayout
• Add components
• Attach listeners
• Implement the listeners
• Inner class
• Implements an interface

6
What is a Listener?

• Objects which are notified when a particular
  event occurs
• Customized reaction to the event, provided by the
  GUI designer
• Examples of events choosing a button, entering
  text, mouse actions, window actions
• Standardized set of methods (an interface) that
  the listener must implement
• will be called by the system automatically
• Must be attached to a GUI component
• Has an Event object passed as a parameter
• evt.getSource()
• returns the object involved in the event
• evt.getActionCommand()
• returns the text associated with object involved
  in the event

7
Examples of GUI in the Mini-Project

• GUI components
• JButton
• JLabel
• JPanel
• JTextArea
• JScrollPane
• Layout
• GridLayout (top panel)
• FlowLayout (bottom panel - default layout)
• BoxLayout (whole)

• Listeners/Inner Classes
• ClearButtonListener
• LookupListener
• CheckOutListener

8
Building the GUI in the Mini-Project

• Declare components
• private JButton lookupButton new
  JButton("Lookup")
• Choose, construct and set the layout
• entryPanel.setLayout(new GridLayout(3, 3,))
• Add components
• entryPanel.add(this.lookupButton)
• Attach listeners
• this.lookupButton.addActionListener(new
  LookupListener())
• Implement the listeners
• private class LookupListener implements
  ActionListener
• public void actionPerformed(ActionEvent e)
• model.doCommand(Library.LOOKUP
  _TITLE, enterTitle.getText())
• //actionPerformed