Lecture 12 Objectives

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Lecture 12 Objectives

• Learn about applets.
• Explore the class Graphics.
• Learn about the class Font.
• Explore the class Color.
• Learn to use additional layout managers.
• Become familiar with more GUI components.
• Learn how to create menu-based programs.
• Explore how to handle key and mouse events.

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Inheritance Hierarchy of GUI Classes
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Constructors and Methods of the class Component
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Constructors and Methods of the class Component
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Constructors and Methods of the class Component
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Constructors and Methods of the class Component
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Applets

• A Java program that is embedded within a Web page
  and executed by a Web browser.
• Create an applet by extending the class JApplet.
• class JApplet is contained in package javax.swing.

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Applets
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Applets
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Applets

• No main method.
• Methods init, start, and paint guaranteed to be
  invoked in sequence.
• To develop an applet
• Override any/all of the methods above.

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Applet Methods

• init method
• Initializes variables.
• Gets data from user.
• Places various GUI components.
• paint method
• Performs output.

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Skeleton of a Java Applet
import java.awt.Graphics import
javax.swing.JApplet public class WelcomeApplet
extends JApplet
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Applet Displaying Welcome Message
//Welcome Applet import java.awt.Graphics impor
t javax.swing.JApplet public class
WelcomeApplet extends JApplet public void
paint(Graphics g) super.paint(g)
//Line 1 g.drawString("Welcome
to Java Programming" , 30,
30) //Line 2
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HTML to Run Applet
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class Font

• Shows text in different fonts.
• Contained in package java.awt.
• Available fonts
• Serif/Sans Serif
• Monospaced
• Dialog/DialogInput
• Arguments for constructor
• String specifying the font face name.
• int value specifying font style.
• int value specifying font size.
• Expressed in points (72 points 1 inch) .

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class Font
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class Color

• Shows text in different colors.
• Changes background color of component.
• Contained in package java.awt.

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class Color
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class Color
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class Color
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class Graphics

• Provides methods for drawing items such as lines,
  ovals, and rectangles on the screen.
• Contains methods to set the properties of graphic
  elements including clipping areas, fonts, and
  colors.
• Contained in the package java.awt.

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class Graphics
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Constructors and Methods for the class Graphics
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Constructors and Methods for the class Graphics
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Constructors and Methods for the class Graphics
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Constructors and Methods for the class Graphics
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Differences Between Applets and GUI Applications

• Applets
• Derived from JApplet.
• No main method.
• Uses init method.
• Displayed by HTML.
• Sets title in HTML.
• Size set in HTML.
• Applet closes when HTML doc closes.

• GUI applications
• Class extends JFrame.
• Invokes main method.
• Uses constructors.
• Uses method setVisible.
• Uses setTitle method.
• Uses method setSize.
• Closes with Exit button.

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Converting a GUI Application to an Applet

• Change JFrame to JApplet.
• Change constructor to method init.
• Remove method calls such as setVisible, setTitle,
  setSize.
• Remove the method main.
• If applicable, remove Exit button and all code
  associated with it (for example, action listener).

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Additional GUI Components

• JTextArea
• JCheckBox
• JRadioButton
• JComboBox
• JList

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JTextArea

• Can collect multiple lines of input from user.
• Can display multiple lines of output.
• Pressing Enter key separates lines of text.
• Each line ends with newline character (\n).
• Derived from class JTextComponent.

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JTextArea
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JTextArea
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JTextArea Example
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JCheckBox

• User selects from predefined values.
• Example of a toggle button.
• Clicking JCheckBox generates item event.
• Use interface ItemListener and its abstract
  method itemStateChanged to handle event.

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JCheckBox
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Constructors and Methods of class JCheckBox
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Constructors and Methods of class JCheckBox
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JRadioButton

• Created same way as check boxes.
• Placed in content pane of applet.
• Forces user to select only one radion button at a
  time.
• You create a button group to group radio buttons.
• Generates an ItemEvent.
• interface ItemListener and method
  itemStateChanged used to handle events.

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JRadioButton
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JRadioButton
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JComboBox

• Commonly known as a drop-down list.
• Used to select an item from a list of
  possibilities.
• Generates an ItemEvent.
• Event monitored by ItemListener.
• ItemListener invokes method itemStateChanged.

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JComboBox
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JComboBox
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JList
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JList
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Layout Managers

• FlowLayout
• Default layout manager.
• Places components from left to right until no
  more items can be placed.
• Can align each line left, center, or right.
• Default alignment LEFT.
• GridLayout
• Similar to FlowLayout.
• All rows (columns) have same number of
  components.
• All components have the same size.

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Layout Managers

• BorderLayout
• Items placed into one of five specific regions
• NORTH/SOUTH
• EAST/WEST
• CENTER
• NORTH and SOUTH components extend horizontally
  (completely span one edge to the other).
• EAST and WEST components extend vertically
  between components in NORTH and SOUTH regions.
• CENTER component expands to occupy any unused
  regions.

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Menus

• Allow for various functions without cluttering
  GUI with too many components.
• Can be attached to objects such as JFrame and
  JApplet (setJMenuBar method).
• To set a menu bar
• private JMenuBar menuMB
• new JMenuBar()
• setJMenuBar(menuMB)
• Add menus to menu bar add menu items to menu.
• Order of menus added order of appearance.

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Keyboard and Mouse Events
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Lecture 12 Summary

• Creating applets
• class Font
• class Graphics
• class Color
• Differences between applets and GUI applications
• Converting GUI applications to applets

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Lecture 12 Summary

• GUI components
• JTextArea
• JCheckBox
• JRadioButton
• Layout managers
• Menus
• Keyboard and mouse events