JAVA Programming

1
JAVA Programming

• GUI Components

2
GUI

• Graphical user interface
• User-friendly design of pictorial depictions for
  use of an application
• Intuitive user interface components
• Reduces time required to learn an application
• Provides basic familiarity and ease of use
  without any instruction

3
GUI Components

• Controls or widgets
• Object with which the user interacts via the
  mouse, keyboard, voice recognition
• Examples
• Labels
• Text fields
• Buttons
• Checkboxes
• Comboboxes
• Lists

4
Swing Package

• javax.swing
• Include classes for GUI components
• Standard for Java 2 Platform
• Can use classes to create a uniform look and feel
  across all platforms
• Lightweight components (written completely in
  Java and do not take the complex GUI capabilities
  of an o/s into consideration)

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Awt package

• java.awt (Abstract Windowing Toolkit)
• Focuses on the local platforms graphical user
  interface capabilities
• Applications are displayed differently based on
  the operating system
• Heavyweight components Rely on the local
  platforms windowing system to determine
  functionality

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Component Class

• Defines the common attributes and behaviors of
  all subclasses of Component
• paint, repaint, update
• Most GUI components extend the Component class
  directly or indirectly
• JComponent is the superclass to most Swing
  components
• Customizable look and feel on different o/s
• Shortcut keys (mnemonics)
• Common event-handling capabilities
• Tool tips
• Localization for different languages

7
JLabel

• Provide text instructions or information on a GUI
• Subclass of JComponent
• Displays a single line of read-only text, an
  image or both text and an image
• setToolTipText specifies a tool tip displayed
  when the mouse is positioned over the label
• setIcon Supports the display of icons on a label
• getText retrieves current text displayed on a
  label
• setText sets the text displayed on the label
• getIcon retrieves the current icon displayed on
  the label
• setHorizontalTextPosition or setVerticalTextPositi
  on specifies the text position on the label
• Fig 13.4

8
Event-Handling

• GUIs generate events when the user of the program
  interacts with the GUI
• An event is sent to the program
• GUI Event information is stored in an object of a
  class that extends AWTEvent

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Event Handling Parts

• Event Source
• GUI component that the user interacts
• Event object
• Encapsulates information about the event that
  occurred with a reference to the event source and
  specific event information that may be required
  by the listener
• Event listener
• Object notified by the event source when an event
  occurs. Object is used to respond to the event

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Programmers Work

• Register an event listener for the GUI component
  expected to generate an event
• Object of a class that implements one or more of
  the event listener interfaces from package
  java.awt.event and javax.swing.event
• Implement an event handler method that is called
  in response to a particular type of event
• Thus, when an event occurs, the GUI component
  with which the user interacted notifies its
  registered listeners by calling each listeners
  appropriate event handling method
• Fig 13.6

11
JTextField

• Single-line areas that allow the user to enter
  text from the keyboard
• When user enters data into JTextField and presses
  the Enter key, an action event occurs.
• Class JTextField extends class JTextComponent
  (javax.swing.text)
• setEditable whether or not the user can modify
  the text
• Fig 13.7

12
JButton

• Component the user clicks to trigger an action
• Command buttons generate an ActionEvent when the
  user clicks the button with the mouse
• Inherits from class AbstractButton
• Text on face of JButton is considered the button
  label
• Fig 13.10

13
JCheckBox and JRadioButton

• Subclasses of JToggleButton
• JRadioButton several buttons of which only one
  can be true at a time (mutually exclusive)
• Two states selected and not selected
• JCheckBox several buttons of which many can be
  true at the same time
• Fig 13.11
• Fig 13.12

14
JComboBox

• Drop-down list of items from which the user can
  make a selection
• Inherits from class JComponent
• Elements in the list have a numeric index to
  track the ordering of items in the combobox
• First item is added at index 0 (similar to
  arrays)
• setMaximumRowCount set the maximum of elements
  displayed when the user clicks the JComboBox
  (determines when to display the scrollbar)
• Fig 13.13

15
JList

• Displays a series of items from which user may
  select one or more items
• Created with class JList which inherits from
  JComponent
• Single-selection (allow only one item to be
  selected at a time)
• Multiple-selection (allow any number of items to
  be selected)
• Do not provide a scrollbar if there are more
  items in the list than the number of visible rows
  (must use JScrollPane)

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JList Methods and Attributes

• setVisibleRowCount determine the of items
  visible in the list
• setSelectionMode
• SINGLE_SELECTION (only 1 item can be selected at
  a time)
• SINGLE_INTERVAL_SELECTION (multiple-selection
  where several items in a contiguous range can be
  selected)
• MULTIPLE_INTERVAL_SELECTION (multiple-selection
  where no restrictions are placed on the
  selections)

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Mouse Event-Handling

• Mouse events can be trapped for any GUI component
  that derives from the java.awt.Component
• MouseListener methods
• mousePressed mouse button is pressed with the
  mouse cursor on the component
• mouseClicked mouse button is pressed and
  released on a component
• mouseReleased mouse button is released after
  being pressed
• mouseEntered mouse cursor enters the bounds of a
  component

18
MouseListener Methods

• mouseDragged mouse button is pressed with the
  mouse cursor on the component and the mouse is
  moved
• mouseMoved mouse is moved with the cursor on the
  component
• Fig 13.17