Java Programming: From Problem Analysis to Program Design, 4e Chapter 12 Advanced GUIs and Graphics.

Java Programming: From Problem Analysis to Program Design, 4e

Chapter 12Advanced GUIs and Graphics

Java Programming: From Problem Analysis to Program Design, 4e 2

Chapter Objectives

• Learn about applets

• Explore the class Graphics• Learn about the class Font• Explore the class Color


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


Inheritance Hierarchy of GUI Classes


Constructors and Methods of the class Component


Constructors and Methods of the class Component (continued)






Constructors and Methods of the class Container


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


Members of class JApplet


Members of class Japplet (continued)


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


Applet Methods

• init Method– Initializes variables– Gets data from user– Places various GUI components

• paint Method– Performs output


Skeleton of a Java Applet

import java.awt.Graphics;import javax.swing.JApplet;

public class WelcomeApplet extends JApplet{

}


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 }}


HTML to Run Applet


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)


Constructors and Methods of the class Font


Constructors and Methods of the class Font (continued)


Constructors and Methods of the class Font (continued)


class Color

• Shows text in different colors

• Changes background color of component

• Contained in package java.awt


Constructors of the class Color


Constructors of the class Color (continued)


Constants Defined in the class Color


Constants Defined in the class Color (continued)


Constants Defined in the class Color (continued)


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


Constructors and Methods of the class Graphics


Constructors and Methods of the class Graphics (continued)














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


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)


Additional GUI Components

• JTextArea• JCheckBox• JRadioButton• JComboBox• JList


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


JTextArea (continued)


Methods Inherited by class JTextArea from Parent

class JTextComponent


JTextArea Example


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


Constructors and Methods of class JCheckBox


Constructors and Methods of class JCheckBox (continued)






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


JRadioButton (continued)








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


Constructors of class JComboBox


Applet with JCheckBox, JComboBox, and JRadioButton


Constructors of class JList


Constructors of class Jlist (continued)


Constructors of class Jlist (continued)


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


Layout Managers (continued)• 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


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


Key and Mouse Events


Chapter Summary

• Creating applets• class Font• class Graphics• class Color• Differences between applet and GUI

application

• Converting GUI application to applet


Chapter Summary (continued)

• GUI components– JTextArea– JCheckBox– JRadioButton

• Layout managers

• Menus

• Key and mouse events

Java Programming: From Problem Analysis to Program Design, 4e Chapter 12 Advanced GUIs and Graphics.

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