Programming in Java

1
Programming in Java

• April 3, 2007
• David Goldschmidt, Ph.D.
• Rensselaer Polytechnic Institute
• goldschd_at_strose.edu

2
Week 12 Coverage

• Remaining Assignments
• Project 2 due April 19
• Homework 3 due April 24
• Project 3 due May 2
• Exam 2 on May 1
• Chapter 12 GUI Programming
• Chapter 14 Event-Driven Programming

3
Portability

• The java.awt library contains heavyweight classes
• Implemented via the Java Virtual Machine
• Dependent on target platform
• The javax.swing library contains lightweight
  classes
• Implemented in Java (except for subclasses of
  java.awt.Window and java.awt.Panel)
• Independent of target platform

4
GUI Class Hierarchy (Swing)
5
Container Classes
6
GUI Helper Classes
7
Swing Components
8
Core Swing Components
9
AWT Classes
10
Frames

• A frame is a window not contained inside another
  window

11
Content Frame Delegation

• In Java 1.4, required to add GUI elements to
  content panes
• frame.getContentPane().add(new JButton(OK))
• In Java 1.5, frame delegates automatically to the
  content pane
• frame.add(new JButton(OK))

12
Frames as Containers

• All JFrame objects act as container objects
• GUI objects are added (much like an ArrayList),
  then displayed when requested
• A layout manager describes how GUI objects are to
  be displayed
• FlowLayout
• GridLayout
• BorderLayout
• GridBagLayout

The order in which objects are added matters
to FlowLayout and GridLayout layout managers
13
Color (i)

• The java.awt.Color class represents colors within
  GUI elements and graphics
• Colors are made up of red, blue, green
  components
• java.awt.Color c new Color(255, 0, 128)
• Standard colors are predefined constants in the
  java.awt.Color class
• BLACK, RED, BLUE, YELLOW, GRAY, etc.

14
Color (ii)

• Most GUI components are colorable
• setBackground(Color c)
• setForeground(Color c)

15
Fonts (i)

• Use the java.awt.Font class to work with fonts
• Font font new Font(name, style, pointSize)
• Examples
• Font f1 new Font(Serif, Font.PLAIN, 12)
• Font f2 new Font(SansSerif, Font.BOLD, 16)
• Font f3 new Font(Monospaced,
• Font.BOLD Font.ITALIC,
  16)
• Font f4 new Font(Times New Roman,
  Font.PLAIN, 16)

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Fonts (ii)

• Set a GUI components font
• okButton.setFont(new Font(etc.))
• Find available font names
• GraphicsEnvironment env
• GraphicsEnvironment.getLocalGraphicsEnvironmen
  t()
• String fontNames
• e.getAvailableFontFamilyNames()

17
Borders

• Create a border for any instances of the
  JComponent class
• LineBorder b new LineBorder(Color.RED, 4)
• panel1.setBorder(b)
• panel2.setBorder(new TitleBorder(Student
  Data))

18
Event-Driven Programming (i)

• In event-driven programming, code is executed
  upon activation of events
• Events include mouse movements, mouse clicks,
  mouse drags, keystrokes, timer expirations,
  operating system events, etc.

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Event-Driven Programming (ii)
Source Event TypeUser Action Object Generated C
lick a button JButton ActionEvent Click a check
box JCheckBox ItemEvent, ActionEvent Click a
radio button JRadioButton ItemEvent,
ActionEvent Press return on a text
field JTextField ActionEvent Select a new
item JComboBox ItemEvent, ActionEvent Window
opened, closed, etc. Window WindowEvent Mouse
pressed, released, etc. Component MouseEvent Key
released, pressed, etc. Component KeyEvent
20
Adapters

• Listeners are typically interfaces, therefore
  requiring all methods be implemented
• Use an adapter class to provide convenience
  implementations of unused methods
• addWindowListener(new WindowAdapter()
• public void windowActivated(WindowEvent
  event)
• System.out.println("Window
  activated")
• )

21
Event-Driven Programming (iii)

• Listener classes respond to actions
• e.g. override the java.awt.event.actionPerformed()
  method
• Listener classes must be registered with the GUI
  objects they are listening for
• e.g. via the okButton.addActionListener() method

22
Inner Classes (i)

• An inner class is a class defined within a class
• Visible only to the surrounding outer class
• Can access outer class data members and methods
• Useful when a specific helper class is required
  (e.g. to implement a listener in
  GUI programming)
• Inner classes may be declared public, private, or
  protected and follow the same visibility rules as
  data members and methods

23
Inner Classes (ii)
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Inner Classes (iii)

• An inner class defined as static may be accessed
  outside the outer class
• A static inner class cannot access non-static
  data members or methods of its outer class

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Mouse Events (i)
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Mouse Events (ii)
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Keyboard Events

• Capture keyboard events via the KeyListener
  interface
• keyPressed(KeyEvent e)
• keyReleased(KeyEvent e)
• keyTyped(KeyEvent e)

Home VK_HOME Page Up VK_PGUP Page Down VK_PGDN
Arrow Keys VK_UP VK_DOWN VK_RIGHT VK_LEFT
28
Timer Events

• Use timers (the java.awt.Timer class) to control
  animations, trigger other events, etc.