java chapter 15

7/27/2019 Java chapter 15

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(C) 2010 Pearson Education, Inc. All rights reserved.

Java How to Program, 8/e


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(C) 2010 Pearson Education, Inc. !! rig"ts re


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A graphical user interface (GI)presents a user!

friendl" #echanis# for interacting $ith an application.

Pronounced %G&&!ee'

Gives an application a distinctive %loo' and %feel.'

Consistent, intuitive user!interface co#ponents give users a

sense of fa#iliarit"

earn ne$ applications #ore *uicl" and use the# #ore

productivel".


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7/231(C) 2010 Pearson Education, Inc. !! rig"ts re

+uilt fro# GI co#ponents.

o#eti#es called controlsor $idgets-short for $indo$

gadgets.

ser interacts via the #ouse, the e"oard or another

for# of input, such as voice recognition.

I/Es

Provide GI design tools to specif" a co#ponents eact sie

and location in a visual #anner " using the #ouse.

Generates the GI code for "ou.

Greatl" si#plifies creating GIs, ut each I/E has different

capailities and generates different code.



Ea#ple of a GI3 $inget4 application (5ig. 17.1)

http://download.java.net/javadesktop/swingset3/Swin

title arat top contains the $indo$s title.

#enu arcontains #enus(Fileand View). In the top!right region of the $indo$ is a set ofuttons

8"picall", users press uttons to perfor# tass.

In the GUI Componentsarea of the $indo$ is a co#o

o9

ser can clic the do$n arro$ at the right side of the o to select

fro# a list of ite#s.
http://download.java.net/javadesktop/swingset3/SwingSet3.jnlphttp://download.java.net/javadesktop/swingset3/SwingSet3.jnlp



:ava E ; update 10


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8hree $a"s to use


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8o set sinstallation folder. If "ou are using an I/E that depends on the :/> (e.g.,


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8o select


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Bost applications use $indo$s or dialog oes(also called

dialogs) to interact $ith the user.

JOptionPane(pacage java".swing) providespreuilt dialog oes for input and output

/ispla"ed via static%&ption'ane#ethods.

5igure 17.2 uses t$o input dialogsto otain integers fro#

the user and a #essage dialogto displa" the su# of the

integers the user enters.


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%&ption'anestatic#ethod showInputDialogdispla"s an input dialog, using the #ethods Stringargu#entas a pro#pt. 8he user t"pes characters in the tet field, then clics OKor presses the

Entere" to su#it the Stringto the progra#. Clicing OKdis#isses (hides)the dialog. Can input onl" Strings. 8"pical of #ost GI co#ponents. If the user clics Cancel, returns null.%&ption'anedialog are dialog-the user cannot interact $ith the rest

of the application $hile dialog is displa"ed.


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Converting Strings to intalues (ntegerclasss static#ethod parse(ntconverts its Stringargu#ent

to an intvalue. Bessage /ialogs

%&ption'anestatic#ethod showMessageDialogdispla"s a #essagedialog.

8he first argu#ent helps deter#ine $here to position the dialog. If null, the dialog o is displa"ed at the center of "our screen. 8he second argu#ent is the #essage to displa". 8he third argu#ent is the Stringthat should appear in the title ar at the top

of the dialog. 8he fourth argu#ent is the t"pe of #essage dialog to displa".


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Bessage /ialogs A JOption-Pane.PLAIN_MESSAGE dialog does not

displa" an icon to the left of the #essage.

%&ption'aneonline docu#entation3http://java.sun.com/javase/!/docs/api/java"/s
http://java.sun.com/javase/6/docs/api/javax/swing/JOptionPane.htmlhttp://java.sun.com/javase/6/docs/api/javax/swing/JOptionPane.html


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$ing GI co#ponentslocated in pacagejavax.swing.

Bost are pure :ava co#ponents =ritten, #anipulated and displa"ed co#pletel" in :ava.

Part of the :ava 5oundation Classes (:5C)for cross!platfor# GIdevelop#ent.

:5C and :ava destop technologies3http://java.sun.com/javase/technologies/desktop/
http://java.sun.com/javase/technologies/desktop/http://java.sun.com/javase/technologies/desktop/


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Astract =indo$ 8oolit (A=8)in pacage java.awtisanother set of GI co#ponents in :ava. =hen a :ava application $ith an A=8 GI eecutes on different :ava

platfor#s, the applications GI co#ponents displa" differentl" on eachplatfor#.

8ogether, the appearance and the $a" in $hich the user interacts$ith the application are no$n as that applications loo!and!feel.

$ing GI co#ponents allo$ "ou to specif" a unifor# loo!and!feel for "our application across all platfor#s or to use each

platfor#s custo# loo!and!feel.


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Bost $ing co#ponents are not tied to actual GIco#ponents of the underl"ing platfor#. >no$n as light$eight co#ponents.

A=8 co#ponents are tied to the local platfor# and are

called heav"$eight co#ponents, ecause the" rel" on thelocal platfor#s $indo$ing s"ste#to deter#ine theirfunctionalit" and their loo!and!feel.

everal $ing co#ponents are heav"$eight co#ponents.


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Class o!ponent(pacage java.awt) declares#an" of the attriutes and ehaviors co##on to theGI co#ponents in pacages java.awtandjava".swing.

Bost GI co#ponents etend class )omponentdirectl" or indirectl".

&nline docu#entation3http://java.sun.com/javase/!/docs/api/java/aw
http://java.sun.com/javase/6/docs/api/java/awt/Component.htmlhttp://java.sun.com/javase/6/docs/api/java/awt/Component.html


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Class ontaine"(pacage java.awt) is a suclass of)omponent. )omponents are attached to )ontainers so that the" can e

organied and displa"ed on the screen. An" oDect that is a )ontainercan e used to organie other

)omponents in a GI. +ecause a )ontaineris a )omponent, "ou can place)ontainers in other )ontainers to help organie a GI.

&nline docu#entation3http://java.sun.com/javase/!/docs/api/java/awt/)onta
http://java.sun.com/javase/6/docs/api/java/awt/Container.htmlhttp://java.sun.com/javase/6/docs/api/java/awt/Container.html


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Class Jo!ponent(pacage java".swing) is asuclass of )ontainer.

%)omponentis the superclass of all light$eight$ing co#ponents, all of $hich are also

)ontainers.


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o#e co##on light$eight co#ponent features supported" %)omponentinclude3pluggable look- and- feelShortcut keys (called mnemonics!"ommon event- handling capabilities for components that initiate the

same actions in an application.

tool tipsSupport for accessibilitySupport for user- interface locali#ation

&nline docu#entation3http://java.sun.com/javase/!/docs/api/java"#/s

wing/%)omponent.html


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Bost $indo$s that can contain $ing GI co#ponents areinstances of class %rameor a suclass of %rame.

%rameis an indirect suclass of class java.awt.+indow Provides the asic attriutes and ehaviors of a $indo$

a title ar at the top

uttons to #ini#ie, #ai#ie and close the $indo$ Bost of our ea#ples $ill consist of t$o classes

a suclass of %ramethat de#onstrates ne$ GI concepts an application class in $hich maincreates and displa"s the

applications pri#ar" $indo$.


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In a large GI /ifficult to identif" the purpose of ever" co#ponent.

Provide tet stating each co#ponents purpose.

uch tet is no$n as a laeland is created $ith class

JLa#el-a suclass of %)omponent. /ispla"s read!onl" tet, an i#age, or oth tet and an i#age.


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%rames constructor uses its Stringargu#ent as thetet in the $indo$s title ar.

Bust attach each GI co#ponent to a container, such as a%rame.

ou t"picall" #ust decide $here to position each GIco#ponent. >no$n as specif"ing the la"out of the GI co#ponents.

:ava provides several la"out #anagersthat can help "ou positionco#ponents.


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Ban" I/Es provide GI design tools in $hich "ou canspecif" the eact sie and location of a co#ponent

I/E generates the GI code for "ou Greatl" si#plifies GI creation 8o ensure that this oos ea#ples can e used $ith an"

I/E, $e did not use an I/E to create the GI code =e use :avas la"out #anagers in our GI ea#ples


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$lowLa%out GI co#ponents are placed on a container fro# left to right in the order in

$hich the progra# attaches the# to the container. =hen there is no #ore roo# to fit co#ponents left to right, co#ponents

continue to displa" left to right on the net line. If the container is resied, a lowLa,outreflo$s the co#ponents to

acco##odate the ne$ $idth of the container, possil" $ith fe$er or #ore ro$s

of GI co#ponents. Bethod setLa%outis inherited fro# class )ontainer.

argu#ent #ust e an oDect of a class that i#ple#ents the La,out-anagerinterface (e.g., lowLa,out).


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%Labelconstructor can receive a Stringspecif"ing thelaels tet.

Bethod set&ool&ip&ext(inherited " %Labelfro#%)omponent) specifies the tool tip that is displa"ed $henthe user positions the #ouse cursor over a %)omponent(such as a %Label).

ou attach a co#ponent to a container using the a''#ethod, $hich is inherited indirectl" fro# class)ontainer.


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Icons enhance the loo!and!feel of an application and are alsoco##onl" used to indicate functionalit".

An icon is nor#all" specified $ith an I(onargu#ent to aconstructor or to the co#ponents setI(on#ethod.

An (conis an oDect of an" class that i#ple#ents interface

(con(pacage java".swing). I!ageI(on(pacage java".swing) supports several i#age

for#ats, including Graphics Interchange 5or#at (GI5), Portale


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get)lass.get0esource1bug2.png1 Invoes #ethod getlass(inherited indirectl" fro# class &bject)

to retrieve a reference to the )lassoDect that represents theLabelrameclass declaration.


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A %Labelcan displa" an (con. %Labelconstructor can receive tet and an (con.

8he last constructor argu#ent indicates the Dustification of the laelscontents.

Interface Swingonstants(pacage java".swing) declares a setof co##on integer constants (such as Swing)onstants.L4) that

are used $ith #an" $ing co#ponents. +" default, the tet appears to the right of the i#age $hen a lael

contains oth tet and an i#age. 8he horiontal and vertical align#ents of a %Labelcan e set $ith

#ethods set*o"i+ontalAlign!entandset,e"ti(alAlign!ent, respectivel".


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Class %Labelprovides #ethods to change a laels appearanceafter it has een instantiated. Bethod set&extsets the tet displa"ed on the lael. Bethod get&extretrievesF the current tet displa"ed on a lael. Bethod setI(onspecifies the (conto displa" on a lael.

Bethod getI(onretrievesF the current (condispla"ed on alael. Bethods set*o"i+ontal&extPositionandset,e"ti(al&extPositionspecif" the tet position in thelael.


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+" default, closing a $indo$ si#pl" hides the $indo$. Calling #ethod setDeaultloseOpe"ation(inherited

fro# class %rame) $ith the argu#entJ$"a!e.EI&_ON_LOSEindicates that the progra# shouldter#inate $hen the $indo$ is closed " the user.

Bethod setSi+especifies the $idth and height of the $indo$in piels.

Bethod set,isi#le$ith the argu#ent truedispla"s the$indo$ on the screen.


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GIs are event driven. =hen the user interacts $ith a GI co#ponent, the

interaction-no$n as an event-drives the progra# to

perfor# a tas.

8he code that perfor#s a tas in response to an event is

called an event handler, and the overall process of

responding to events is no$n as event handling.


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J&ext$iel'sand JPasswo"'$iel's(pacagejava".swing).

%4e"tieldetendsclass J&exto!ponent(pacagejava".swing.te"t), $hich provides #an" features co##onto $ings tet!ased co#ponents.

Class %'asswordieldetends %4e"tieldand adds#ethods that are specific to processing pass$ords.

%'asswordieldsho$s that characters are eing t"ped as theuser enters the#, ut hides the actual characters $ith an echocharacter.


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=hen the user t"pes data into a %4e"tieldor a%'asswordield, then pressesEnter, an eventoccurs.

ou can t"pe onl" in the tet field that is %in focus.'

A co#ponent receives the focus $hen the user clics

the co#ponent.


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+efore an application can respond to an event for aparticular GI co#ponent, "ou #ust perfor# several

coding steps3"reate a class that represents the event handler.

$mplement an appropriate interface% known as an event-listener interface% in the class from St ep 1.

$ndicate that an ob&ect of the class from Steps ' and 2 shouldbe notified when the event occurs. his is known as registeringthe event handler.


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All the classes discussed so far $ere so!called top!levelclasses-that is, the" $ere not declared inside another

class.

:ava allo$s "ou to declare classes inside other classes

-these are called nested classes. Can e staticor non!static.


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+efore an oDect of an inner class can e created, there #ust firste an oDect of the top!level class that contains the inner class.

8his is re*uired ecause an inner!class oDect i#plicitl" has areference to an oDect of its top!level class.

8here is also a special relationship et$een these oDects-the

inner!class oDect is allo$ed to directl" access all the varialesand #ethods of the outer class.

A nested class that is staticdoes not re*uire an oDect of itstop!level class and does not i#plicitl" have a reference to anoDect of the top!level class.


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Inner classes can e declared public, protectedor private.

ince event handlers tend to e specific to the

application in $hich the" are defined, the" are often

i#ple#ented as privateinner classes.


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GI co#ponents can generate #an" events in responseto user interactions.

Each event is represented " a class and can e

processed onl" " the appropriate t"pe of event

handler.


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=hen the user pressesEnter in a %4e"tieldor%'asswordield, an A(tionEvent(pacagejava.awt.event) occurs.

Processed " an oDect that i#ple#ents the interfaceA(tionListene"(pacage java.awt.event).

8o handle Actionvents, a class #ust i#ple#entinterface ActionListenerand declare #ethodaction'erformed. 8his #ethod specifies the tass to perfor# $hen an Actionvent

occurs.


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Bust register an oDect as the event handler for eachtet field.

a''A(tionListene"registers an

ActionListeneroDect to handle

Actionvents. After an event handler is registered the oDect listens

for events.


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8he GI co#ponent $ith $hich the user interacts is theevent source. Actionvent#ethod getSource(inherited fro# classvent&bject) returns a reference to the event source.

Actionvent#ethod getA(tiono!!an'otains

the tet the user t"ped in the tet field that generated theevent. %'asswordield#ethod getPasswo"'returns the

pass$ords characters as an arra" of t"pe char.


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5igure 17.11 illustrates a hierarch" containing #an"event classes fro# the pacage java.awt.event.

sed $ith oth A=8 and $ing co#ponents.

Additional event t"pes that are specific to $ing GI

co#ponents are declared in pacage

javax.swing.event.


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/elegation event #odel-an events processing is delegated toan oDect (the event listener) in the application. 5or each event!oDect t"pe, there is t"picall" a corresponding

event!listener interface. Ban" event!listener t"pes are co##on to oth $ing and A=8

co#ponents. uch t"pes are declared in pacage java.awt.event, and so#e of

the# are sho$n in 5ig. 17.12. Additional event!listener t"pes that are specific to $ing

co#ponents are declared in pacage java".swing.event.


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Each event!listener interface specifies one or #oreevent!handling #ethods that #ust e declared in the

class that i#ple#ents the interface.

=hen an event occurs, the GI co#ponent $ith $hich

the user interacted notifies its registered listeners "calling each listeners appropriate event!handling

#ethod.


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o$ the event!handling #echanis# $ors3 Ever" %)omponenthas a variale listenerListthat

refers to an EventListene"List(pacagejava".swing.event).

Baintains references to registered listeners in the

listenerList. =hen a listener is registered, a ne$ entr" is placed in the

co#ponents listenerList. Ever" entr" also includes the listeners t"pe.


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o$ does the GI co#ponent no$ to callaction'erformedrather than another #ethodH Ever" GI co#ponent supports several event t"pes, including #ouse

events, e" eventsand others.

=hen an event occurs, the event is dispatchedonl" to the event

listeners of the appropriate t"pe. /ispatching is si#pl" the process " $hich the GI co#ponent calls

an event!handling #ethod on each of its listeners that are registeredfor the event t"pe that occurred.


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Each event t"pe has one or #ore corresponding event!listenerinterfaces.Actionvents are handled " ActionListeners MouseEventsare handled " MouseListene"sandMouseMotionListene"s

/e%Eventsare handled " /e%Listene"s

=hen an event occurs, the GI co#ponent receives (fro# the:B) a uni*ue event I/specif"ing the event t"pe. 8he co#ponent uses the event I/ to decide the listener t"pe to $hich the

event should e dispatched and to decide $hich #ethod to call on eachlistener oDect.


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5or an Actionvent, the event is dispatched to ever"registered ActionListeners action'erformed#ethod.

5or a -ouse#vent, the event is dispatched to ever"

registered -ouseListeneror-ouse-otionListener, depending on the #ouse eventthat occurs.

8he -ousevents event I/ deter#ines $hich of the several#ouse event!handling #ethods are called.


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Auttonis a co#ponent the user clics to trigger a specificaction. everal t"pes of uttons

co##and uttons checoes

toggle uttons radio uttons +utton t"pes are suclasses of A#st"a(t0utton

(pacage java".swing), $hich declares the co##onfeatures of $ing uttons.


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A co##and utton generates an Actionvent$henthe user clics it.

Co##and uttons are created $ith class J0utton.

8he tet on the face of a %5uttonis called auttonlael.


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A %5uttoncan displa" an (con. A %5uttoncan also have a rolloverI(on displa"ed $hen the user positions the #ouse over the %5utton. 8he icon on the %5uttonchanges as the #ouse #oves in and out

of the %5uttons area on the screen. Abstract5utton#ethod

set)ollove"I(on

specifies the i#age displa"ed on the %5utton$hen theuser positions the #ouse over it.


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%5uttons, lie %4e"tields, generateActionvents that can e processed " an"ActionListeneroDect.


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8hree t"pes of state uttons-J&oggle0utton,Jhe(10oxand J)a'io0utton-that have onoffor truefalse values.

Classes %)heck5o"and %0adio5uttonare

suclasses of %4oggle5utton. %0adio5uttons are grouped together and are#utuall" eclusive-onl" one in the group can eselected at an" ti#e


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%4e"tield#ethod set$ont(inherited " %4e"tieldindirectl" fro#class )omponent) sets the font of the %4e"tieldto a ne$ $ont(pacage java.awt).

Stringpassed to the %)heck5o"constructor is the checo laelthatappears to the right of the %)heck5o"" default.

=hen the user clics a %)heck5o", an Ite!Eventoccurs. andled " an Ite!Listene"oDect, $hich #ust i#ple#ent #ethod

ite!Statehange'. An (temListeneris registered $ith #ethod a''Ite!Listene". %)heck5o"#ethod isSele(te'returns trueif a %)heck5o"is

selected.


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?adio uttons(declared $ith class %0adio5utton) are si#ilarto checoes in that the" have t$o states-selected and notselected (also called deselected).

?adio uttons nor#all" appear as a groupin $hich onl" oneutton can e selected at a ti#e.

electing a different radio utton forces all others to e

deselected. sed to represent #utuall" eclusiveoptions. 8he logical relationship et$een radio uttons is #aintained " a0uttonG"oupoDect (pacage java".swing), $hichorganies a group of uttons and is not itself displa"ed in a user

interface.


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5utton6roup#ethod a''associates a%0adio5utton$ith the group.

If #ore than one selected %0adio5uttonoDect isadded to the group, the selected one that $as added

first $ill e selected $hen the GI is displa"ed. %0adio5uttons, lie %)heck5o"es, generate(temvents $hen the" are cliced.


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A co#o o(or drop!do$n list) enales the user toselect one ite# fro# a list.

Co#o oes are i#ple#ented $ith class

Jo!#o0ox, $hich etends class %)omponent. %)ombo5o"es generate (temvents.


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8he first ite# added to a %)ombo5o"appears as the currentl"selected ite# $hen the %)ombo5o"is displa"ed.

&ther ite#s are selected " clicing the %)ombo5o", thenselecting an ite# fro# the list that appears.

%)ombo5o"#ethod setMaxi!u!)owountsets the

#ai#u# nu#er of ele#ents that are displa"ed $hen the userclics the %)ombo5o". If there are additional ite#s, the %)ombo5o"provides a

scrollarthat allo$s the user to scroll through all the ele#ents inthe list.


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An anon"#ous inner classis an inner class that is declared$ithout a na#e and t"picall" appears inside a #ethoddeclaration.

As $ith other inner classes, an anon"#ous inner class canaccess its top!level classs #e#ers.

An anon"#ous inner class has li#ited access to the localvariales of the #ethod in $hich its declared. ince an anon"#ous inner class has no na#e, one oDect of

the anon"#ous inner class #ust e created at the point$here the class is declared.


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%)ombo5o"#ethod getSele(te'In'exreturnsthe inde of the selected ite#. 5or each ite# selected fro# a %)ombo5o", another

ite# is first deselected-so t$o (temvents occur$hen an ite# is selected.

(temvent#ethod getStatehangereturns thet"pe of state change. (temvent.SL)4$indicates that an ite# $as selected.


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A list displa"s a series of ite#s fro# $hich the user#a" select one or #ore ite#s. ists are created $ith cla%List, $hich directl"

etends class %)omponent.ss

upports single!selection lists(onl" one ite# to eselected at a ti#e) and #ultiple!selection lists(an"nu#er of ite#s to e selected).

%Lists generate ListSele(tionEvents insingle!selection lists.


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set,isi#le)owountspecifies the nu#er of ite#s visilein the list.

setSele(tionMo'especifies the lists selection #ode. Class ListSele(tionMo'el(of pacage java".swing)

declares selection!#ode constants SINGLE_SELE&ION(onl" one ite# to e selected at a ti#e)

SINGLE_IN&E),AL_SELE&ION(allo$s selection of severalcontiguous ite#s)

M2L&IPLE_IN&E),AL_SELE&ION(does not restrict the ite#s thatcan e selected).


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nlie a %)ombo5o", a %Listdoes notprovide ascrollar if there are #ore ite#s in the list than thenu#er of visile ro$s. A JS("ollPaneoDect is used to provide the scrolling

capailit".

a''ListSele(tionListene"registers aListSele(tionListene"(pacagejava".swing.event) as the listener for a%Listsselection events.


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Each %rameactuall" consists of three la"ers-the acground, the content

pane and the glass pane. 8he content pane appears in front of the acground and is $here the GI

co#ponents in the %rameare displa"ed. 8he glass pane is displa"s tool tips and other ite#s that should appear in front

of the GI co#ponents on the screen. 8he content pane co#pletel" hides the acground of the %rame.

8o change the acground color ehind the GI co#ponents, "ou #ust changethe content panes acground color.

Bethod get)ontent'anereturns a reference to the %rames content pane(an oDect of class )ontainer).

List#ethod getSele(te'In'exreturns the selected ite#s inde.


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A #ultiple!selection listenales the user to select #an" ite#s fro# a

%List. A S(N6L7(N408AL7SL)4(&Nlist allo$s selecting a

contiguous range of ite#s. 8o do so, clic the first ite#, then press and hold the Shift e" $hile clicing the

last ite# in the range. A -9L4('L7(N408AL7SL)4(&Nlist (the default) allo$s

continuous range selection as descried for aS(N6L7(N408AL7SL)4(&Nlist and allo$s #iscellaneousite#s to e selected " pressing and holding the Ctrl e" $hile clicingeach ite# to select. 8o deselect an ite#, press and hold the Ctrl e" $hile clicing the ite# a second

ti#e.


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If a %Listdoes not contain ite#s it $ill not dipla" in a

lowLa,out. use %List#ethods set$ixe'ell3i'thand set$ixe'ell*eightto

set the ite# $idth and height 8here are no events to indicate that a user has #ade #ultiple selections

in a #ultiple!selection list. An event generated " another GI co#ponent (no$n as an eternal event)

specifies $hen the #ultiple selections in a %Listshould e processed. Bethod setListDatasets the ite#s displa"ed in a %List. -ethod getSele(te',aluesreturns an arra" of &bjects

representing the selected ite#s in a %List.


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MouseListene"and MouseMotionListene"event!listener interfaces for handling #ouse events. An" GI co#ponent

Pacage java".swing.eventcontains interfaceMouseInputListene", $hich etends interfaces-ouseListenerand -ouse-otionListenerto create asingle interface containing all the #ethods.

-ouseListenerand -ouse-otionListener#ethodsare called $hen the #ouse interacts $ith a )omponentifappropriate event!listener oDects are registered for that)omponent

.


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Each #ouse event!handling #ethod receives a MouseEvent

oDect that contains infor#ation aout the #ouse event thatoccurred, including thex- and"!coordinatesof the location$here the event occurred.

Coordinates are #easured fro# the upper!left corner of the GIco#ponent on $hich the event occurred.

8he !coordinates start at 0 and increase fro# left to right. 8he y!coordinates start at 0 and increase fro# top to otto#. 8he #ethods and constants of class InputEvent(-ouse#vents superclass) enale "ou to deter#ine $hich #ouseutton the user cliced.


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Interface Mouse3heelListene"enalesapplications to respond to the rotation of a #ouse$heel.

Bethod !ouse3heelMove'receives aMouse3heelEventas its argu#ent.

Class -ouse+heelvent(a suclass of -ouse#vent) contains #ethods that enale the event handlerto otain infor#ation aout the a#ount of $heelrotation.


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(C) 2010 Pearson Education Inc !! rig"ts re


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0o"'e"La%outarranges co#ponents into five regions3NO)&*, SO2&*, EAS&, 3ES&and EN&E).

5orderLa,outsies the co#ponent in the )N40to use allavailale space that is not occupied

Bethods a''MouseListene"and

a''MouseMotionListene"register -ouseListenersand -ouse-otionListeners, respectivel". -ousevent#ethods getand get4return thex-andy!

coordinates of the #ouse at the ti#e the event occurred.


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Ban" event!listener interfaces contain #ultiple #ethods.

An adapter classi#ple#ents an interface and provides a

default i#ple#entation ($ith an e#pt" #ethod od") of

each #ethod in the interface.

ou etend an adapter class to inherit the defaulti#ple#entation of ever" #ethod and override onl" the

#ethod(s) "ou need for event handling.


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A #ouse can have one, t$o or three uttons. Class -ouseventinherits several #ethods fro#(nputventthat can distinguish a#ong #ouse

uttons or #i#ic a #ultiutton #ouse $ith a co#ined

e"stroe and #ouse!utton clic. :ava assu#es that ever" #ouse contains a left #ouse

utton.


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8he nu#er of consecutive #ouse clics is returned "-ousevent#ethod getli(1ount. Bethods isMetaDownand isAltDowndeter#ine

$hich #ouse utton the user cliced.


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se a %'anelas a dedicated dra$ing areain $hich the user candra$ " dragging the #ouse.

ight$eight $ing co#ponents that etend class %)omponent(such as %'anel) contain #ethod painto!ponent called $hen a light$eight $ing co#ponent is displa"ed

&verride this #ethod to specif" ho$ to dra$. Call the superclass version of paint)omponentas the first state#ent

in the od" of the overridden #ethod to ensure that the co#ponentdispla"s correctl".


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%)omponentsupport transparenc". 8o displa" a co#ponent correctl", the progra# #ust deter#ine $hether

the co#ponent is transparent.

8he code that deter#ines this is in superclass %)omponentspaint)omponenti#ple#entation.

=hen a co#ponent is transparent, paint)omponent$ill not clear its

acground =hen a co#ponent is opa*ue, paint)omponentclears the

co#ponents acground

8he transparenc" of a $ing light$eight co#ponent can e set $ith#ethod setOpa5ue(a falseargu#ent indicates that the co#ponentis transparent).


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Class Point(pacage java.awt) represents anx-ycoordinate. =e use oDects of this class to store the coordinates of each #ouse

drag event.

Class G"aphi(sis used to dra$.

-ousevent#ethod getPointotains the 'oint$here the event occurred. Bethod "epaint(inherited fro# )omponent) indicates

that a )omponentshould e refreshed on the screen assoon as possile.


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6raphics#ethod illOvaldra$s a solid oval. 5our para#eters represent a rectangular area (called the ounding

o) in $hich the oval is displa"ed.

8he first t$o are the upper!left !coordinate and the upper!lefty-coordinate of the rectangular area.

8he last t$o represent the rectangular areas $idth and height.

Bethod fill&valdra$s the oval so it touches the #iddleof each side of the rectangular area.


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i i f f h dli


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e,Listenerinterface for handling e" events.

>e" events are generated $hen e"s on the e"oard are pressed and released. A e,Listener#ust define #ethods 1e%P"esse', 1e%)elease'and1e%&%pe' each receives a e,ventas its argu#ent

Class e,ventis a suclass of (nputvent. Bethod ke,'ressedis called in response to pressing an" e".

Bethod ke,4,pedis called in response to pressing an" e" that is not anaction e". Bethod ke,0eleasedis called $hen the e" is released after an"ke,'ressedor ke,4,pedevent.


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? i t t h dl ith th d ''/ Li t f


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?egisters e" event handlers $ith #ethod a''/e%Listene"fro#

class )omponent. e,vent#ethod get/e%o'egets the virtual e" codeof thepressed e".

e,ventcontains virtual e"!code constants that represents ever"e" on the e"oard.

alue returned " gete,)odecan e passed to static

e,vent#ethod get/e%&extto get a string containing the na#eof the e" that $as pressed.

e,vent#ethod get/e%ha"($hich returns a char) gets thenicode value of the character t"ped.

e,vent#ethod isA(tion/e%deter#ines $hether the e" in theevent $as an action e".

B th d tM 'ii d t i h th difi


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Bethod getMo'iie"sdeter#ines $hether an" #odifier

e"s (such as Shift, Alt andCtrl) $ere pressed $hen the e"event occurred. ?esult can e passed to statice,vent#ethodget/e%Mo'iie"s&extto get a string containing the na#es ofthe pressed #odifier e"s.

(nputvent#ethods isAltDown, isont"olDown,isMetaDownand isShitDowneach return abooleanindicating $hether the particular e" $as pressedduring the e" event.

t GI t i t i


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a"out #anagersarrange GI co#ponents in a container

for presentation purposes Can use for asic la"out capailities Enale "ou to concentrate on the asic loo!and!feel-the

la"out #anager handles the la"out details. a"out #anagers i#ple#ent interface La%outManage"

(in pacage java.awt). )ontainers setLa,out#ethod taes an oDect that

i#ple#ents the La,out-anagerinterface as anargu#ent.


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8here are three $a"s for "ou to arrange co#ponents in

a GI3

)bsolute positioning*reatest level of control.

Set )ontainer+s layout to null.

Specify the absolute position of each *,$ component withrespect to the upper- left corner of the )ontainerby using)omponentmethods setSi;eand setLocationorset5ounds.

ust specify each *,$ component+s si#e.

t


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ayout managers

Simpler and faster than absolute positioning.

ose some control over the si#e and the precise positioning of*,$ components.

/isual programming in an $01

,se tools that make it easy to create *,$s.)llows you to drag and drop *,$ components from a tool bo

onto a design area.

3ou can then position% si#e and align *,$ components as youlike.


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l L t i th i l t l t


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lowLa,outis the si#plest la"out #anager. GI co#ponents placed fro# left to right in the order in

$hich the" are added to the container.

=hen the edge of the container is reached, co#ponents

continue to displa" on the net line.

lowLa,outallo$s GI co#ponents to e left aligned,centered (the default) and right aligned.


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lowLa,out #ethod setAlign!ent changes the


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lowLa,out#ethod setAlign!entchanges thealign#ent for the lowLa,out. $lowLa%out.LE$&

$lowLa%out.EN&E)

$lowLa%out.)IG*&

La,out-anagerinterface #ethod la%outontaine"($hich is inherited " all la"out #anagers) specifies that a

container should e rearranged ased on the adDusted la"out.

5orderLa,out


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,

the default la"out #anager for a %frame arranges co#ponents into five regions3 N&04


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5orderLa,out constructor argu#ents specif" the


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5orderLa,outconstructor argu#ents specif" thenu#er of piels et$een co#ponents that are

arranged horiontall" (horiontal gap space) and

et$een co#ponents that are arranged verticall"

(vertical gap space), respectivel".

8he default is one piel of gap space horiontall" and

verticall".


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G"i'La%outdivides the container into a grid of ro$s and


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g

colu#ns. I#ple#ents interface La,out-anager. Ever" )omponenthas the sa#e $idth and height. Co#ponents are added starting at the top!left cell of the grid and

proceeding left to right until the ro$ is full. 8hen the processcontinues left to right on the net ro$ of the grid, and so on.

)ontainer#ethod vali'atereco#putes thecontainers la"out ased on the current la"out #anager andthe current set of displa"ed GI co#ponents.


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Co#ple GIs re*uire that each co#ponent e placed in an


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eact location. &ften consist of #ultiple panels, $ith each panels co#ponents arranged

in a specific la"out. Class %'aneletends %)omponentand %)omponent

etends class )ontainer, so ever" %'anelis a )ontainer. Ever" %'anel#a" have co#ponents, including other panels,

attached to it $ith )ontainer#ethod add. %'anelcan e used to create a #ore co#ple la"out in $hich

several co#ponents are in a specific area of another container.


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A J&extA"eaprovides an area for #anipulating


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p p g

#ultiple lines of tet. %4e"tAreais a suclass of %4e"t)omponent,

$hich declares co##on #ethods for %4e"tields,%4e"tAreas and several other tet!ased GIco#ponents.


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A J&extA"eaprovides an area for #anipulating


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#ultiple lines of tet. %4e"tAreais a suclass of %4e"t)omponent.


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0oxis a suclass of )ontainerthat uses a 0oxLa%outto arrange the GIco#ponents horiontall" or verticall".


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p " " 5o"static#ethod ("eate*o"i+ontal0oxcreates a 5o"that arranges

co#ponents left to right in the order that the" are attached. %4e"tArea#ethod getSele(te'&ext(inherited fro#%4e"t)omponent) returns the selected tet fro# a %4e"tArea.

%4e"tArea#ethod set4e"tchanges the tet in a %4e"tArea. =hen tet reaches the right edge of a %4e"tAreathe tet can $rap to the

net line. ?eferred to as line $rapping.

+" default, %4e"tAreadoes not $rap lines.

ou can set the horiontal and vertical scrollar


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policiesof a %Scroll'ane$hen its constructed. ou can also use %Scroll'ane#ethodsset*o"i+ontalS("oll0a"Poli(% and

set,e"ti(alS("oll0a"Poli(%to change the

scrollar policies.

Class %Scroll'anedeclares the constants%Scroll'ane.804()AL S)0&LL5A0 AL+AS


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%Scroll'ane.804()AL7S)0&LL5A07AL+AS%Scroll'ane.&N4AL7S)0&LL5A07AL+AS

to indicate that a scrollar should al$a"s appear, constants%Scroll'ane.804()AL7S)0&LL5A07AS7N$$%Scroll'ane.&N4AL7S)0&LL5A07AS7N$$

to indicate that a scrollar should appear onl" if necessar" (the defaults) andconstants%Scroll'ane.804()AL7S)0&LL5A07N80%Scroll'ane.&N4AL7S)0&LL5A07N80

to indicate that a scrollar should never appear. If polic" is set to &N4AL7S)0&LL5A07N80, a%4e"tAreaattached to the %Scroll'ane$ill auto#aticall" $raplines.

java chapter 15

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