Software Construction Lecture 11 GUI Programming in Java

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Software ConstructionLecture 11GUI Programming
in Java
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GUI Programming Concepts

• conventional programming
• sequence of operations is determined by the
  program
• what you want to happen, happens when you want it
• event-driven programming
• sequence of operations is determined by the
  users interaction with the applications
  interface
• anything that can happen, happens at any time

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GUI Design Concepts

• Principles of good GUI Design
• IBM's Design concepts
• Saul Greenberg's HCI pages
• Tim's HCI notes

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GUI Programming Concepts in Java

• Java GUI has components
• Windows GUI has controls
• Unix GUI has widgets
• examples labels, buttons, check boxes, radio
  buttons, text input boxes, pull down lists
• Swing components JLabel, JButton, JCheckBox,
  JRadioButton, JTextField, JTextArea, JComboBox

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Java GUI history the AWT

• AWT(JDK 1.0, 1.1) Abstract Window Toolkit
• package java.awt, java.awt.event
• heavyweight components using native GUI system
  elements
• used for applets until most browsers supported
  JRE 1.2

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Swing in Java

• Swing(Java 2, JDK 1.2)
• lightweight components that do not rely on the
  native GUI or OS
• look and feel of Swing components
• are identical on different platforms
• can be customized
• Swing inherits from AWT
• AWT still used for events, layouts

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Swing Components in Java

• advanced GUI support. e.g. drag-and-drop
• package names javax.swing, javax.swing.event
• components inherit from JComponent
• components are added to a top-level container
  JFrame, JDialog, or JApplet.

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running a Swing application

• java -Dswing.aatexttrue MySwingClass
• the option sets the system property
  "swing.aatext" to "true" to enable anti-aliasing
  for every JComponent
• javaw runs a GUI without the console window

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Basic GUI Programming Stepsin Java

• declare a container and components
• add components to one or more containers using a
  layout manager
• register event listener(s) with the components
• create event listener method(s)

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Basic GUI Programming Concepts in Java

• Example JFrameDemo.java, JFrameDemoTM.java
• container a screen window/applet window/panel
  that groups and arranges GUI components
• GUI component an object with visual
  representation
• Swing containers JFrame, JApplet, JPanel
• AWT containers Frame, Applet, Panel

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GUI Programming The Java Approach

• event-driven programming
• a piece of code (i.e. event handler) is attached
  to a GUI component
• an event handler is called when an event (e.g. a
  mouse click) is activated / fired
• The Delegation Event Model in Java
• processing of an event is delegated to an object
  (the listener) in the program

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Event-driven Programming in Java

• event source a GUI component that generates /
  fires an event
• event a user interaction (e.g. a click on
  the button)
• event listener an object that has encapsulated
  event handlers to react to an event

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Event Handling in Java

• the delegation event model
• - a GUI element delegates the processing of
  an event to another piece of code (i.e. an event
  handler)
• - the event source generates/fires an event and
  sends it to event listeners

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Event Handling in Java

• the delegation event model
• - event listeners must be registered with an
  event source in order to receive
  notification
• Example JButtonDemo.java,
  JButtonDemo2.java

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Event Handling in Java

• registration of an event listener
• - write a class that implements an ltevent
  namegtListener interface - create an
  instance of that class (i.e. an event
  listener) - register the listener with a
  GUI component addltevent namegtListener
  ( ltan event listenergt )

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Event Handling in Java

• a listener interface has a list of standard event
  handlers (i.e. methods)
• API documentation - java.awt.event -
  event classes - listener interfaces -
  adapter classes

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Event Handling in Java

• different ways of coding the event listeners
• - use of another top-level class JButtonDemo
• - anonymous inner classes JButtonDemo2,
  JFrameDemo, JFrameDemo2
• - use of an adapter class JFrameDemo3
• JFrameDemoTM2.java uses named inner classes and
  shows how to consolidate window closing from two
  different events.

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Handling of Mouse Events

• MouseListener mousePressed( ), mouseClicked(
  ) mouseReleased( ), mouseEntered(
  ) mouseExited( )
• MouseMotionListener mouseDragged( ),
  mouseMoved( )
• MouseAdapter, MouseMotionAdapter
• Example MouseDemo.java

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Multiple Event Sources

• Example ActionApplet2.java .html
• one listener for multiple event sources
• GUI and graphics programming
• http//cs.senecac.on.ca/pliu/appletdemo.html

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Review

• GUI
• Java GUI
• Components
• Event Listeners
• Delegates
• Event Sources