Chapter 10 Writing Graphical User Interfaces

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Chapter 10Writing Graphical User Interfaces
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Understanding Javas GUI Classes
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• Java has two sets of GUI classes
• Original GUI class AWT Abstract Window
  Toolkit
• Located in java.awt package
• Updated GUI class Swing
• Located in javax.swing
• Both contain classes to create controls
• Windows
• Push buttons
• Text fields
• Menus

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Understanding Javas GUI Classes
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Understanding Javas GUI Classes
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Understanding Javas GUI Classes
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• Style and appearance of GUI components are called
  their look and feel
• AWT classes adopt look and feel of the local
  platform
• With Swing you have the option of using local
  platform look and feel or a standard look and
  feel (called metal)
• Both AWT and Swing take advantage of inheritance

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Understanding Javas GUI Classes
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Using AWT Classes

• Class definition of a GUI generally follows the
  structure you used for a problem domain class
• One difference is that you create an instance of
  GUI and make it visible
• Write statements to instantiate GUI components
• Then write statements to add them to the window

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Creating a Window with a Button

• Frame inheritance hierarchy is Windows,
  Container, and Component
• Your GUI inherits from all three super classes
• Need to import the AWT package import
  java.awt.
• Class is a subclass of Frame must extend the
  Frame classpublic class AWTFrameWithButton
  extends Frame

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Creating a Window with a Button
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• Constructor must accomplish five tasks
• Create and instance of Button
• Add the button to the frame
• Establish the frame size
• Place a title on the frame
• Make the frame visible

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Creating a Window with a Button
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Using Layout Managers

• AWT includes several classes called layout
  managers
• Used to determine how components are positioned
  on containers such as frames and panels
• Most frequently used layout managers
• FlowLayout
• BorderLayout
• GridLayout

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Using Layout Managers
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• To use
• Instantiate the manager you want to use
• Invoke the setLayout method, passing a reference
  to the layout manager you want to use
• Components placed on a container using the
  BorderLayout manager expand to fill the space
  available

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Using Layout Managers
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Using Layout Managers

• FlowLayout manager places components on the frame
  as you add them, left to right
• GridLayout manager arranges the container into a
  grid consisting of rows and columns
• When you instantiate you need to specify the
  number of rows and columns you want to have

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Using Layout Managers
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Handling Java Events

• Users interact with GUI by entering data and
  clicking on components
• An event is a signal that the user has taken some
  action
• Event is also an instance of a class such as
  MouseEvent, WindowEvent, etc.

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Handling Java Events
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Handling Java Events

• Event listener registers with event source by
  invoking a method in the event source
• Button events are called action events
  registration method is named addActionListener
• Next step is to write a method to handle the
  event for buttons this method is actionPerformed

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Handling Java Events

• There are three methods for handling events
• Implementing interfaces
• Extending Adapter classes
• Creating Inner classes

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Implementing Interfaces

• When you implement an interface you must override
  all of its methods
• Implement the appropriate interface for the event
• Write methods to override the interfaces methods
  and deal with the events
• Interface for buttons is ActionListener
• Need to import interface import
  java.awt.event.

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Implementing Interfaces
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Extending Adapter Class

• Second way of dealing with events is to use an
  adapter class
• Supplied class that implements a listener
  interface, and then overrides all of the
  interface methods with null methods
• Most override methods you want to respond to
• Need to create two classes one that extends
  Frame, and another that extends WindowAdapter

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Extending Adapter Class
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Creating Inner Classes
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• Third way of dealing with events is to use an
  anonymous inner class
• Anonymous inner class is an inner class without a
  name
• Used to simplify code needed to handle events
• See pp. 336

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Creating Inner Classes
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Creating Inner Classes
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Creating Inner Classes
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• When you compile an inner class the compiler
  produces two class files
• If your outer class is named Outer and your inner
  class is named Inner a filed called
  OuterInner.class is created
• If the inner class is anonymous, the class file
  for the inner class has the same name as the
  outer class with a number beginning with 1
  concatenated after the

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Converting an Application to an Applet

• An applet is a class you write that extends the
  Applet class
• Runs under the control of a web browser
• Can convert AWTFrameAndComponent to an applet by
• Delete the main method
• Delete all references to close button
• Delete the anonymous inner class
• Delete the shutDown method
• Delete the setVisible, setSize, and setTitle
  methods

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Converting an Application to an Applet
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Using Swing Classes

• Swing classes are newer improved versions of the
  original AWT classes
• Want to use for there improved appearance and
  capability

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Converting AWT GUI to Swing
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• Swing components reside in javax.swing import
  javax.swing.
• Change class names of Button, Label, TextField,
  and Panel to JButton, JLabel, JTextField, and
  JPanel
• Use JFrame instead of Frame
• Compare Figure 10-17 vs. Figure 10-14

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Converting AWT GUI to Swing
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AWT
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Adding Drop-down Menus
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• Swing drop down menus consist of three classes
• JMenuBar
• JMenu
• JMenuItem
• See Figure 10-20 on page 352

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Adding Drop-down Menus
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Converting a Swing Application to an Applet

• Steps for conversion include
• Extend JApplet instead of JFrame
• Delete the main method
• Delete all references to close menu item
• Delete the anonymous inner class
• Delete the shutDown method
• Delete the statements setVisible, setSize, and
  setTitle

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Converting a Swing Application to an Applet