chapter11-graphicalcomponents

8/22/2019 Chapter11-GraphicalComponents

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Graphical User

InterfaceComponents: Part 1

Chapter11


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What You Will Learn

Swing Components

Event handling

Mouse event handling


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Graphical User Interface (GUI)

Gives program distinctive look and feel

Provides users with basic level of familiarity

Built from GUI components (controls,

widgets, etc.)

o User interacts with GUI component via mouse,

keyboard, etc

Check out this visual indexof components
http://java.sun.com/docs/books/tutorial/uiswing/components/components.htmlhttp://java.sun.com/docs/books/tutorial/uiswing/components/components.html


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Netscape Window With GUI

Components

menu barbutton combo boxmenus

scroll bars


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Dialog Boxes

Used by applications to interact with the user

Provided by Javas JOptionPane classo Contains input dialogs and message dialogs

View example program, Figure 11.2

Title Bar

Prompt to

user

Text field

which allows

user input

When user clicks OK,

dialog box dismissed
http://www.letu.edu/people/stevearmstrong/cosc2103/lectures/CodeSamplesCh11SimpleGUI/CodeSamplesCh11.htmhttp://www.letu.edu/people/stevearmstrong/cosc2103/lectures/CodeSamplesCh11SimpleGUI/CodeSamplesCh11.htm


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Dialog Boxes

Note icon

Other icons availableMessage dialog type Icon Description

ERROR_MESSAGE A dialog that indicates an error to the user.

INFORMATION_MESSAGE A dialog with an informational message to theuser.WARNING_MESSAGE A dialog warning the user of a potentialproblem.

QUESTION_MESSAGE A dialog that poses a question to the user. Thisdialog normally requires a response, such as

clicking aYes or a No button.

PLAIN_MESSAGE no icon

A dialog that contains a message, but no icon.


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Some Basic GUI Components

Component Description

JLabel Displays uneditable text or icons.JTextField Enables user to enter data from the keyboard. Can also be used to

display editable or uneditable text.

JButton Triggers an event when clicked with the mouse.JCheckBox Specifies an option that can be selected or not selected.JComboBox Provides a drop-down list of items from which the user can make a

selection by clicking an item or possibly by typing into the box.

JList Provides a list of items from which the user can make a selection byclicking on any item in the list. Multiple elements can be selected.

JPanel Provides an area in which components can be placed and organized.Can also be used as a drawing area for graphics.


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Overview

Swing GUI componentso Declared in package javax.swingo Most are pure Java componentso Part of the Java Foundation Classes (JFC)

Abstract Window Toolkit (AWT)

o Precursor to Swingo Declared in package java.awto Does not provide consistent, cross-platform look-

and-feel


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Lightweight

vs. Heavyweight

Lightweight components

o Not tied directly to GUI components supportedby underlying platform

Heavyweight components

o Tied directly to the local platformo AWT components

o Some Swing components


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Superclasses of Swings

Lightweight GUI ComponentsClass Component

o (package java.awt)o Subclass ofObjecto Declares many behaviors and attributes common

to GUI components


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Lightweight GUI ComponentsClass Container

o (package java.awt)o Subclass ofComponento Organizes Components


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Lightweight GUI ComponentsClass JComponent

o (package javax.swing)o Subclass ofContainero Superclass of all lightweight Swing components


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Common Lightweight Component

Features Pluggable look-and-feel

o customize the appearance of components

Shortcut keyso mnemonics

Common event-handling capabilities

Brief description of components purposeo tool tips

Support for localization


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Displaying Text and Images in a

WindowClass JFrame

o Most windows are an instance or subclass of this

classo Provides title bar

o Provides min, max, close buttons

Labelo Text instructions or information stating the

purpose of each component

o Created with class JLabel


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Three Parts of a GUI Application

1. Components that make up the Graphical

User Interface

2. Listeners that receive the events andrespond to them

3. Application code that does useful work for

the user


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Events Generated by Swing

ComponentsAct that results in the event Listener type

User clicks a button, presses Returnwhile typing in a text field, or chooses a

menu item

ActionListener

User closes a frame (main window) WindowListener

User presses a mouse button while thecursor is over a component

MouseListener

User moves the mouse over acomponent

MouseMotionListener

Component becomes visible ComponentListener

Component gets the keyboard focus FocusListener

Table or list selection changes ListSelectionListener


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Events Generated by Swing

Components Each event is represented by an object

o Object gives information about the event

o Identifies the event source.

Event sources are typically components,o Other kinds of objects can also be event sources.

Each event source can have multiple listeners

registered on it.o Conversely, a

single listener canregister withmultiple event sources.


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JLabel

Labelo Provide text on GUI

o Defined with class JLabelo Can display:

Single line of read-only text

Image Text and image

View Figure 11.6o

Note uses of the JLabel Class


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Creating and Attaching label1Method setToolTipText of classJComponent

o Specifies the tool tip

Method add of class Containero Adds a component to a container


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Creating and Attaching label2Interface Icon

o Can be added to a JLabel with the setIconmethod

o Implemented by class ImageIcon


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Creating and Attaching label2Interface SwingConstants

o Declares a set of common integer constants

such as those used to set the alignment of

components

o Can be used with methodssetHorizontalAlignment andsetVerticalAlignment


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Creating and Attaching label3OtherJLabel methods

o getText and setText For setting and retrieving the text of a label

o getIcon and setIcon For setting and retrieving the icon displayed in the

label

o getHorizontalTextPosition andsetHorizontalTextPosition For setting and retrieving the horizontal position of the

text displayed in the label


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Some basic GUI Components.

Constant Description

Horizontal-position constants

SwingConstants.LEFT Place text on the left.SwingConstants.CENTER Place text in the center.SwingConstants.RIGHT Place text on the right.Vertical-position constantsSwingConstants.TOP

Place text at the top.SwingConstants.CENTER Place text in the center.SwingConstants.BOTTOM Place text at the bottom.


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OtherJFrameMethods setDefaultCloseOperation

o Dictates how the application reacts when the

user clicks the close button setSize

o Specifies the width and height of the window

setVisibleo Determines whether the window is displayed

(true) or not (false)


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Event Handling

An event occurs every time the usero Types a character or

o Pushes a mouse button

Any object can be notified of the event.

That object must:o Implement the appropriate interface

o Be registered as an event listeneron the

appropriate event source.


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Event Handling

GUI's are event driveno Events occur when user interacts with GUI

o e.g., moving mouse, pressing button, typing intext field, etc.

Class java.awt.AWTEvent Checkout Sun tutorialon event handling
http://java.sun.com/docs/books/tutorial/uiswing/overview/event.htmlhttp://java.sun.com/docs/books/tutorial/uiswing/overview/event.html


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Some Event Classes Of Package

java.awt.event


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Event Handling Model

Three partso Event source

GUI component with which user interactso Event object

Encapsulates information about event that occurred

o Event listener

Receives event object when notified, then responds Programmer must perform two tasks

o Register event listener for event source

o Implement event-handling method (event handler)


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Event Listener Object

When a GUI program is running, each actionof the user generates an event

The following are some types of events:o Moving the mouse

o Clicking the mouse on a button

o Typing some text into a text area

For a program to respond to an event theremust be an event listener object in the GUIprogram that listens to that type of event


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What is an Event Listener?

An event listener is an objecto It "listens" for events from a specific GUI

component (itself an object) When an event is generated by the GUI

component

oA method in the listener object is invoked torespond to the event


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What If ?

When there is no event listener for an event

oA program can ignore events

o If there is no listener for an event, the event is

just ignored

When a tree falls in

the forest and there's

no one present tohear it, does it make a

sound?


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Event-

listenerInterfaces

Of Packagejava.awt.event


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Textfields

JTextFieldo Single-line area in which user can enter text

JPasswordFieldo Extends JTextField

o Hides characters that user enters

View Figure 11.9, Test Program 11.10o Illustrates capabilities of textfields

o Note helpon handling number fields
http://www.letu.edu/people/stevearmstrong/cosc2103/lectures/CodeSamplesCh11SimpleGUI/CodeSamplesCh11.htmhttp://www.letu.edu/people/stevearmstrong/cosc2103/lectures/CodeSamplesCh11SimpleGUI/CodeSamplesCh11.htmhttp://java.sun.com/developer/JDCTechTips/2001/tt1120.htmlhttp://java.sun.com/developer/JDCTechTips/2001/tt1120.htmlhttp://www.letu.edu/people/stevearmstrong/cosc2103/lectures/CodeSamplesCh11SimpleGUI/CodeSamplesCh11.htmhttp://www.letu.edu/people/stevearmstrong/cosc2103/lectures/CodeSamplesCh11SimpleGUI/CodeSamplesCh11.htm


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How Event Handling Works

You must register the event handlero Through components method

addActionListener


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How Event Handling Works

The component knows to call

actionPerformedbecause

o Event is dispatched only to listeners ofappropriate type

o Each event type has corresponding event-

listener interface Event ID specifies event type that occurred


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Event Registration for

JTextField textField1


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JButton

Buttono Component user clicks to trigger a specific action

o Several different types Command buttons Check boxes Toggle buttons

Radio buttonso javax.swing.AbstractButton subclasses

Command buttons are created with class JButton GenerateActionEvents when user clicks button


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Swing Button Hierarchy


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JButton Example

View, ButtonFrame class, Figure 11.15 Test program, Figure 11.16

Look foro Declaration of the buttons

o Inner class ButtonHandler which does eventhandling for the button

o Call to .addActionListener(handler)method registers buttons to receive events

o The actionPerformed() method
http://www.letu.edu/people/stevearmstrong/cosc2103/lectures/CodeSamplesCh11SimpleGUI/CodeSamplesCh11.htmhttp://www.letu.edu/people/stevearmstrong/cosc2103/lectures/CodeSamplesCh11SimpleGUI/CodeSamplesCh11.htmhttp://www.letu.edu/people/stevearmstrong/cosc2103/lectures/CodeSamplesCh11SimpleGUI/CodeSamplesCh11.htmhttp://www.letu.edu/people/stevearmstrong/cosc2103/lectures/CodeSamplesCh11SimpleGUI/CodeSamplesCh11.htm


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Comments on JButton

To detect when user clicks buttono Program must have an object that implements

ActionListener interface

Program must register object as an actionlistener on the button (the event source)o Using the addActionListener method


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Comments on JButton

When user clicks the button, it fires an actionevent.o Results in the invocation of the action listener's

actionPerformedmethodo The only method in theActionListener

interface

JButtons can have a rollover iconoAppears when mouse is positioned over a button

oAdded to a JButton with methodsetRolloverIcon


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Buttons That Maintain State

Swing contains three types of state buttons

JToggleButton, JCheckBox andJRadioButton

JCheckBox and JRadioButton are

subclasses ofJToggleButton


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JCheckBox

Contains a check box label that appears to right of

check box by default

Generates an ItemEvent when it is clickedo ItemEvents are handled by an ItemListenero Passed to method itemStateChanged

Method isSelectedreturns whether check boxis selected (true) or not (false)View example class Figure 11.17test Figure 11.18

Things to Note:

Declaration ofJCheckBoxreferences

Instantiation ofJCheckBox objects

RegisterJCheckBox's to receive eventsfrom CheckBoxHandler

CheckBoxHandler invokes methoditemStateChanges

Change JTextFieldfont, depending on

which JCheckBox was selected


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JRadioButton

Has two states selected and unselected

Normally appear in a group in which only one radio

button can be selected at onceo Group maintained by a ButtonGroup object

Declares method add to add a JRadioButton to group

Usually represents mutually exclusive options View RadioButtonFrame, Figure 11.19Test

program, Figure 11.20


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Demonstration ofJRadioButton

When viewing Figure 11.19, look for the

following

o Declaration ofJRadioButton referenceso Group specification

o Instantiation ofJRadioButton objects

o Registration ofJRadioButton's to receiveevents

o RadioButtonHandler invokes methoditemStateChanged


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JComboBox

JComboBoxo List of items from which user can select

oAlso called a drop-down list Note features in Figure 11.21

Instantiate JComboBox to show three Strings

from names array at a time RegisterJComboBox to receive events

ItemListener invokes method

itemStateChanged


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JList

A list is a series of itemso User can select one or more items

oSingle-selection vs. multiple-selection

JList demonstration, Figure 11.23o Note use ofColorNames array to populate JList

o Specification ofSINGLE_SELECTION

o Registration ofJList to receive eventso ListSelectionListener invokes methodvalueChanged

o Background set according to user choice


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Multiple-Selection Lists

Multiple-selection list capabilitieso Select many items from Jlist

oAllows continuous range selection

Look for the following in Figure 11.25

Use of ColorNames arrayo Specification ofMULTIPLE_INTERVAL_SELECTION

option

o Use ofJButton and JListCopyList method


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Mouse Events

Create aMouseEvent object

Handled byMouseListeners and

MouseMotionListenersMouseInputListener combines the two

interfaces

InterfaceMouseWheelListener declaresmethodmouseWheelMovedto handleMouseWheelEvents


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Mouse Event Handling

Event-listener interfaces for mouse eventsoMouseListener

oMouseMotionListenero Listen forMouseEvents

In Figure 11.28 note use of

o RegisterJFrame to receive mouse eventso Methods invoked for various mouse events

(Note that program does not seem to perform as

advertised when run under ReadyTo !!?)


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Listener Interfaces

MouseListener and MouseMotionListener interface methods

Methods of interface MouseListener public void mousePressed( MouseEvent event )

Called when a mouse button is pressed while the mouse cursor is on acomponent.

public void mouseClicked( MouseEvent event )Called when a mouse button is pressed and released while the mouse

cursor remains stationary on a component. This event is always

preceded by a call to mousePressed.public void mouseReleased( MouseEvent event )

Called when a mouse button is released after being pressed. This

event is always preceded by a call to mousePressed and one ormore calls to mouseDragged.

public void mouseEntered( MouseEvent event )Called when the mouse cursor enters the bounds of a component.


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Listener Interfaces

MouseListener and MouseMotionListener interface methods

public void mouseExited( MouseEvent event )Called when the mouse cursor leaves the bounds of a component.

Methods of interface MouseMotionListenerpublic void mouseDragged( MouseEvent event )

Called when the mouse button is pressed while the mouse cursor is on

a component and the mouse is moved while the mouse button remains

pressed. This event is always preceded by a call to mousePressed.All drag events are sent to the component on which the user began to

drag the mouse.

public void mouseMoved( MouseEvent event )Called when the mouse is moved when the mouse cursor is on a

component. All move events are sent to the component over which the

mouse is currently positioned.


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Listener Interfaces

Suppose your class directly implements

MouseListener,

o Then you must implement all fiveMouseListener methods.

o Even if you care only about mouse clicks

Methods for those events you don't careabout can have empty bodies.

o Resulting collection of empty method bodies can

make code harder to read and maintain


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Adapter Classes

Solution is to use adapter classes

For example, theMouseAdapter class

implements theMouseListener interface.An adapter class implements empty versions

of all its interface's methods.


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Adapter Classes

To use an adaptero Create a subclass of it, instead of directly

implementing a listener interface.o By extendingMouseAdapter, your class

inherits empty definitions of all five of the

methods thatMouseListener contains.


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Adapter Classes Characteristics of an adapter class

o Implements interface

o Provides default implementation of each interface

methodo Used when all methods in interface is not needed

Event-adapter class in java.awt.event Implements interfaceComponentAdapter ComponentListenerContainerAdapter ContainerListener FocusAdapter FocusListenerKeyAdapter KeyListenerMouseAdapter MouseListenerMouseMotionAdapter MouseMotionListener WindowAdapter WindowListener


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Adapter Classes

Example of use of an adapter classo Figure 11.34, the Painter program

Noteo Registration ofMouseMotionListener to

listen for windows mouse-motion events

o Override methodmouseDragged, but notmethodmouseMoved

o Store coordinates where mouse was dragged,

then repaint JFrame


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ExtendingMouseAdapter

TheMouseDetails.java program,Note example, Figure 11.31

Demonstrateso How to determine the number of mouse clicks

o How to distinguish between different mouse

buttons


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InputEvent Methods

Help distinguish amongo left-,

o center- and

o right-mouse-button clicks

InputEvent method DescriptionisMetaDown() Returnstrue when the user clicks the right mouse button on a

mouse with two or three buttons. To simulate a right-mouse-

button click on a one-button mouse, the user can hold down the

Meta keyon the keyboard and click the mouse button.

isAltDown() Returns true when the user clicks the middle mouse button ona mouse with three buttons. To simulate a middle-mouse-

button click on a one- or two-button mouse, the user can press

the Altkey on the keyboard and click the only- or left-mouse

button, respectively.


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Key Event Handling

Interface KeyListener

Handles key events

o Generated when keys on keyboard are pressedand released

KeyEvent

o Contains virtual key code that represents key Demonstrated in Figure 11.36


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Layout Managers

Layout manager capabilitieso Provided for arranging GUI components

o Provide basic layout capabilitieso Processes layout details

o Programmer can concentrate on basic look and

feelo Interface LayoutManager


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Layout Managers

Layout manager methods

Layout manager Description

FlowLayout Default for javax.swing.JPanel. Places components sequentially(left to right) in the order they were added. It is also possible to

specify the order of the components by using the Container methodadd, which takes a Component and an integer index position asarguments.

BorderLayoutDefault for JFrames (and other windows). Arranges the componentsinto five areas: NORTH, SOUTH, EAST, WEST and CENTER.

GridLayout Arranges the components into rows and columns.


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FlowLayout

Most basic layout manager

GUI components placed in container from

left to right Example program, Figure 11.39

o Layout set as FlowLayout

o Note results as user presses button


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BorderLayout

Arranges components into five regions

o NORTH (top of container)

o SOUTH (bottom of container)o EAST (left of container)

o WEST (right of container)

o CENTER (center of container) View example, Figure 11.41


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GridLayout

Divides container into grid of specified row

an columns

Components are added starting at top-leftcell

o Proceed left-to-fight until row is full

GridLayout demonstration, Figure 11.43o Clicking buttons toggles between different

layouts


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Panels

Helps organize components

Class JPanel is JComponent subclass

May have components (and other panels)added to them

Panel example, Figure 11.45


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Applying Concepts

Suppose you wish to have a GUI which

accomplishes the following

o Enter numbersin text boxes

o Press button

to do

calculations


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Step By Step

View code to create the window

Note

o Class (program) extends JFrameo Constructor sets up window using methods

inherited from JFrame

o Methodmain()instantiates class object


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Add the Text Labels

View additional code

Note

o Declaration, instantiation ofJLabelso Container reference,pane

Gets handle forcontentPaneo

pane layout specifiedo JLabels added


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Add the Text Boxes

View next iteration of code for adding the

JTextFields

Noteo Declaration, instantiation of JTextFields

o Change grid layout of pane for 2 columns

oAdding to pane


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Final Version

View final code version Note

o Declaration, instantiation of buttonso Declaration, definition, instantiation of action

handlers Different author, does not use inner anonymous

classesoAdd action handlers to the buttons

Our program never actually calls the actionhandlers

I l t E t H dl


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Implement an Event Handler

Every event handler requires three bits of code:

1. Code that specifies that the class either1. Implements a listener interface or

2. Extends a class that implements a listener interface.

For example:

public class MyClass implements ActionListener {2. Code that registers an instance of the event

handler class as a listener upon one or morecomponents.For example:someComponent.addActionListener(instanceOfMyClass);

3. Code that implements the methods in the listenerinterface.For example:public void actionPerformed(ActionEvent e)

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