COP3252 Advanced Java Programming

1
COP3252Advanced Java Programming

• 18-Mar-08
• Lecture Set 16
• GridLayout, Menus, JRadioButtons, Graphics and
  Java2D

2
Gridlayout

• Gridlayout positions a containers components in
  a rectangular grid
• Divided into equal sized rectangles
• One component is placed in each rectangle
• Can be added to a JToolBar, JFrame, JPanel, etc.

3
GridLayout Example

• The following example code will produce a 2
  column, three row grid.
• A picture of the result is included on the next
  slide.
• getContentPane().setLayout(new GridLayout(3,2))
• getContentPane().add(new Button("1"))
• getContentPane().add(new Button("2"))
• getContentPane().add(new Button("3"))
• getContentPane().add(new Button("4"))
• getContentPane().add(new Button("5"))
• getContentPane().add(new Button("6"))

4
GridLayout

• Using the example code, the program will produce
  the following display
• http//java.sun.com/j2se/1.5.0/docs/api/java/awt/G
  ridLayout.html

5
Menus

• The File, Edit, Help, etc bar at the top of most
  programs is called a MenuBar.
• Java includes a JMenuBar to allow us to create
  application menus
• The elements of a JMenuBar are called JMenus
• The items (or choices) in a JMenu are called
  JMenuItems

6
Menus

• We first create the JMenuBar
• We must then tell our JFrame to use the MenuBar
• Use the command setJMenuBar(menuBar)
• menubar is whatever you called your JMenuBar
• We then create our menus.
• We then add our MenuItems to the menus (and add
  actions to the MenuItems)
• Finally, we add our menus to the MenuBar.

7
Menu example

• //Create the JMenuBar
• JMenuBar menuBar new JMenuBar()
• //Set the created bar to be the menu bar for this
  frame
• setJMenuBar(menuBar)
• //Create a JMenu called Test
• JMenu menu new JMenu(Test)
• //Add a JMenuItem called item1 to the JMenu
• menu.add(new JMenuItem(item1))
• //Add the menu to the JMenuBar
• menuBar.add(menu)

8
Making an interactive menu

• By default, clicking on a menu item will not do
  anything
• You must assign an action to each button
  (JMenuItem)
• Menu actions can be assigned the same way as any
  other action in JAVA

9
Example

• See JFrameMenuAction.java for a live code example

10
JRadioButtons

• Radio Button An item that can be selected or
  deselected, and which displays its state to the
  user.
• Can be grouped together so that only one button
  at a time can be selected.
• Often used to allow the user to easily choose
  between a set of options.

11
JRadioButton Constructors

• JRadioButton() Creates an initially unselected
  radio button with no set text.
• JRadioButton(String text) Creates an unselected
  radio button with the specified text.
• JRadioButton(String text, boolean selected)
  Creates a radio button with the specified text
  and selection state.

12
Grouping JRadioButtons

• You must group related buttons so that the user
  can only select one at a time
• Use a ButtonGroup to setup a grouping
• Example
• ButtonGroup group1 new ButtonGroup()
• group1.add(radioButton1)
• group1.add(radioButton2)
• etc

13
Which button is selected?

• You will need a way to figure out which button is
  selected.
• JRadioButton has a method called isSelected()
  that returns a boolean value to let you know
  whether the button is selected or not.
• See the example for usage.

14
JRadioButton Example

• File JRadioButtonExample.java
• You will see
• Hitting the go button will cause the program to
  inform the user which button is selected (using a
  JTextField).

15
Basic Graphics and Java2D

• We will discuss the following
• Controlling fonts
• Class Font, FontMetrics
• Controlling colors
• Class Color
• Drawing two-dimensional shapes
• Class Graphics2D, Polygoc, BasicStroke,
  GradientPaint, TexturePaint

16
Javas Coordinate System

• Scheme for identifying every point on the screen
• Standard x-y style coordinate pair
• 0,0 starts are upper-left of GUI component
• Measured in pixels (or Picture Elements)

17
Class Graphics

• Abstract class
• Graphics objects can not be instantiated
• Portability drawing is performed differently on
  different platforms
• When Java is implemented, subclass of graphics is
  created that implements that drawing
  capabilities.
• Implementation is hidden by class Graphics
• Graphics supplies interface so that the
  programmer sees it at platform-independent.

18
paintComponent method

• Class Component is superclass of JComponent
• Contains method paintComponent that takes a
  Graphics object as an argument
• Object is passed to the paintComponent method by
  the system when a LW Swing component needs to be
  repainted.
• paintComponent is seldom called directly by the
  programmer . Usually event-driven
• When GUI app executes, paintComponent is called
  for each LW component as the GUI is displayed.
• To call it again, event must occur (cover/uncover
  components)
• To force execution, call repaint method

19
Drawing lines, rectangles and ovals

• Graphics class includes several methods for
  drawing basic 2D shapes
• Each method requires a non-negative width and
  height value
• See http//java.sun.com/javase/6/docs/api/java/awt
  /Graphics.html

20
PaintComponent example

• See JPanelGraphics.java and JPanelGraphicsTest.jav
  a

21
Working with Fonts

• Class Fonts constructor takes three arguments
• Font name
• Any font currently supported by the system on
  which the program is running (ex Monospaced,
  Serif, etc).
• Font style
• One of the static fields of class Font
• Font.PLAIN, Font.BOLD, Font.ITALIC
• Can be used in combination
• Font.BOLDFont.ITALIC
• Font Size
• int representing point size

22
Working with Fonts

• See FontJPanel.java and FontTest.java

23
The Java 2D API

• Provides advanced 2D graphics capabilities over
  that of the Graphics class
• Graphics2D is an abstract subclass of class
  Graphics
• Includes all capabilities of Graphics class
  discussed earlier
• To access, we must cast the Graphics reference
  (g) passed to paintComponent into a Graphics 2D
  reference
• Graphics2D g2d (Graphics2D)g

24
Java2D Basic Examples

• Refer to pages 636-638 of the course textbook for
  very basic examples
• hopefully on Thursday I can show you some
  advanced examples

25
Java2D Paths

• General Path shape constructed from straight
  lines and complex curves.
• Represented with an object of class GeneralPath
• Allows you to define your own shapes

26
Java2D Paths

• See Path.java and PathTest.java