Analysis to Program Design, 3e

Java Programming: From Problem
Analysis to Program Design, 3e


Chapter 13

Advanced GUIs and Graphics


Java Programming: From Problem Analysis to Program Design, 3e

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Chapter Objectives

•
Learn about applets

•
Explore the
class

Graphics

•
Learn about the
class

Font

•
Explore the
class

Color


Java Programming: From Problem Analysis to Program Design, 3e

3

Chapter Objectives (continued)

•
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
(continued)

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Constructors and Methods of the
class

Component
(continued)

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Constructors and Methods of the
class

Component
(continued)

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Constructors and Methods of the
class

Container

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Applets

•
Applet: 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

contained in package
javax.swing

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Members of
class

JApplet

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Members of
class

Japplet
(continued)

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Applets (continued)

•
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;

import

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/SanSerif

–
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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Constructors and Methods of the
class

Font

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Constructors and Methods of the
class

Font
(continued)

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Constructors and Methods of the
class

Font
(continued)

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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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Constructors of the
class

Color

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Constructors of the
class

Color

(continued)

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Constants Defined in the
class

Color

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Constants Defined in the
class

Color

(continued)

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Constants Defined in the
class

Color

(continued)

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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 area,
fonts, and colors

•
Contained in the package
java.awt

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Constructors and Methods of the
class

Graphics

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Constructors and Methods of the
class

Graphics
(continued)

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Constructors and Methods of the
class

Graphics
(continued)

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32

Constructors and Methods of the
class

Graphics
(continued)

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33

Constructors and Methods of the
class

Graphics
(continued)

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Constructors and Methods of the
class

Graphics
(continued)

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35

Constructors and Methods of the
class

Graphics
(continued)

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36

Constructors and Methods of the
class

Graphics
(continued)

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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/all code
associated with it (e.g. 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

(continued)

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Methods Inherited by
class

JTextArea

from Parent
class

JTextComponent

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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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Constructors and Methods of
class

JCheckBox

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Constructors and Methods of
class

JCheckBox

(continued)

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Constructors and Methods of
class

JCheckBox

(continued)

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Constructors and Methods of
class

JCheckBox

(continued)

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JRadioButton

•
Created same way as check boxes

•
Placed in content pane of applet

•
Forces user to select only one radio 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

(continued)

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JRadioButton

(continued)

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JRadioButton

(continued)

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JRadioButton

(continued)

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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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Constructors of
class

JComboBox

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Applet with
JCheckBox
,
JComboBox
, and
JRadioButton

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Constructors of
class

JList

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Constructors of
class

Jlist

(continued)

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Constructors of
class

Jlist

(continued)

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Layout Managers

•
FlowLayout

–
Default layout manager

–
Places components from left to right, center by default,
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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61

Layout Managers (continued)

•
BorderLayout

–
Items placed into one of 5 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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62

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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Key and Mouse Events

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Chapter Summary

•
Creating Applets

•
class

Font

•
class

Graphics

•
class

Color

•
Differences between Applet and GUI
application

•
Converting GUI application to Applet

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65

Chapter Summary (continued)

•
GUI components

–
JTextArea

–
JCheckBox

–
JRadioButton

•
Layout managers

•
Menus

•
Key and mouse events