head first java second edition phần 7 ppt

Panel AA layout manageris aJava object associated with a particular component, almostalwaysa b ackgroun dcomponent, The layout manager controls the components containedwithin the compone

controller events

import javax sound.Ulidi *;

public class MiniMuaicPlayer2

public static void main(String[] args) (

~n£MusicPlayer2 mini : new MiniMusicPlayar2();

mini-goO ;

Sequence seq = new Sequence (Sequence PPQ, 4) ;

Track track =s&q.createTrack();

(~ -I:h~ CO'I'tr

ol1ty-L -~T'nL~"ty\tha"cilty "'~ ~c:t.,i e'fo/t.~d ~e

.l \" l _ i,,~-tat~. 1 I "r.(

~ ,e"" 'S""' ·. t.KIl tothetD",,,,a,,a- ,

e ,e"t" '/ole'n F'"

public MidiEvent makeEvent (int cOJDd, int chan, int one, int two, int tick) (

MidiEvent event null;

try (

ShortMassage a ~ new ShortNessage():

a.BetM&ssage(comd, chan, on8, two);

evant = new Micli.Event(a, tick);

Version Ihree: drawing graphics in thtte with the tltusic

This final version builds on version two by adding the GUI parts We build a

frame, add a drawing panel to it, and each time we get an event,we draw a

new rectangle and repaint the screen The only other change from version

two is that the notes play randomlyas opposed to simply moving up the

scale

The most important change to the code (besides building a simple GUI)

isthat we make the drawing panel implement the ControllerEventListener

rather than the program itself So when the drawing panel (an inner class)

gets the event, it knows how to take care of itself by drawing the rectangle

Complete code for this version is on the next page

The drawing panel inner class:

I' a list.eYltV'

C Tht clV'a ,iYl~yaYlt 'sclass MyDrawPanel extends JPanel implements ControllerEventListener

boolean msg =false; t r'~Lsd: a.fla~ to.faist,a",d ,~'" Stt i

W 1;1"\OtOI'Ily wht'"Wt g~ta", ~ve",t

public void controlChange(ShortMessage event) (

msg =true; f

repaint () ;r - We~ota",~vtnt, sow~setthe flagto

tl"\Ot and tall l"~pai"'tO

Wehav~tol.lS~ a fla~ b~tal.lS~OT»ER th ·

a",dw~ wanttoDai",iONL\/ h Lh Iln~sCllli~~~ t\"i~~~\" a\"tpainiO,

r T w tn1; ereSa OI'IvolJt\"Evtnt

g.setColor(new Color(r,gr,b»;

Tht I"est istod~ to ~t"'t\"aie

a\"andOllltolO\"and painta

Stllli-\"andolll \"tttan~lt

g.fillRect(x,y,ht, width);

} II close if

you are her e ~ 391

public static void main(String[] args) (

Min1MusicPlayer3 mini = new Min1MusicPlayer3();

sequencer.addControllerEventListener(ml, new int[] {127»;

Sequence seq = new Sequence(Sequence.PPQ, 4);

Track track = seq.createTrack() ;

Who am IP

A bunch of Java hot -shots, in full costume, are playIng the party game-Who

am Ir They give you a clue , and youtryto guess who they are, based on what they say Assume they always tell the truth about themselves If they happen to say something that could be true for more than one guy, then write down allioswhom that sentence applies Fill In the blanks next to the sentence with the names of oneor more attendees

Tonight'sattendees:

Any of the charming personalities from this chapter just might show upl

I got the whole GUI, In my hands

Every event type has one of these

The listener's key method

This method gives JFrame its size

You add codeto this method but never call It

When the user actually does something, It's an _ _

Most of these are event sources

I carry data back to the listener

An addXxxLlstener( ) method says an object is an _ _

How a listener signs up

The method where all the graphics code goes

I'm typically bound to an Instance

The 'g' In (Graphics g), Is really of class

The method that gets palntComponent( ) roiling

The package where most of the Swingers reside

394 chapter 12

public static void main(String II args)

InnerButtan qui =new InnerButton();

guLgo () ;

}

public void gal) {

frame = new JFrame();

class BListener extends ActionListener {

public void actionPerformed(ActionEvent e) {

compiler and detertrtine whether this file

will cOl1Ipile If it won't co11IPile, haw

would you t'xx it, and if it does compile, what would it do?

public static void main(String [I args)InnerButton qui ~ new InnerButton():

qui-go(I:

Who am I?

I got the whole GUI inmyhands JFrame

Every event type has one of these listener interface

The listener's key method actionPerlormed( )

This method givesJFrame its size setSize( )

You add code to this method but

never call it paintCompone.nt( )

a button that toggles between

AandB whenyou click it

When the user actually does

something, it's an _ _ event

Most of these are event sources swing components

I carry data back to the listener; event object

An addXxxListener( ) method

sa ys an obj ect is an _ event source

How a listener signs up addActionListe.ner( )

The method where all the

graphics code goes paintComponent( )

public void go(l {frame =new JFrame();

frame.setDefaultCloseOperation(

JPrame EXIT_ON_CLOSE) ;

The addActionListener( ) method takes a class that implements theActionl.is-

tener interface

b =new JButton("A")j

b addActionLiBtener( lIiWJLlstettar( I )l

I' m typically bound to an instance inner class

ActionListener is an interface interlacesareimplemented, notextended

The ' s'in (Graphics g) is

really of this class.

The method that gets

Work on Your

Swing

Swing is easy. Unless you actuallycarewhere things end up on the screen Swing code

lookseasy,but then you compile it, run it, look at it and think- 'h~y,that'snot supposed to go

there."The thing that makes iteasytocodeIs the thing that makes Ithardtocanuo/-the

layout Manager Layout Manager objects control the size and location of the widgets in a Java GUJ They do a ton of work on your behalf, but you won't always like the results You want two buttons to be the same size,but they aren't You want the text field to be three inches long, but It's nine Or one Andunderthe label instead ofnextto It But with a tittle work, you can get layout managers to submit to your will In th is chapter, we'll work on our Swing and in addition

to layout managers, we'll learn more about wIdgets We'll make them, display them (wherewe

choose), and use themIna program It's not looking 100 good for Suzy

th is is a n ew c h ap te r 399

components and containers

The things you put in a CUI The things a usersees and interacts with.Text

fields,buttons, scrollablelists,radio buttons, etc.areall components.In

fact, theyall extend javax swing JComponent

COlMpo.,etds can be nested

In Swing, virtuallyallcomponents are capable of holding other

components In other words, you can siUkjust about anything into anything

else But most of the time, you'll add userinteractive components such as

buttons and lists intobackground components such as frames and panels.

Although it'spossible to put, say, a panel inside a button, that's pretty

weird, and won't win you any usability awards

With the exception ofJFrame,though, the distinction betweeninteractive

components and ba.ckground components is artificial AJPanel for

example,isusually used as a background for grouping other components,

but even aJPanel can be interactive Just as with other components, you

can register for the JPanel 's events including mouse clicks and keystrokes

A widget is teduucal.l y

a Swing Com~ent._

you can stick in a GUI extends !rom

javaLSWing.JComponent.

Four steps to making a GUI (review)

• Make a window (e JFrame)

JFrame frama "" n_ JFrame () ;

• Make a component (button,textfield, erc.)

JButton button - ne JButton("click meU

) ;

• Add the component to the frame

frame getContantPane () add(BordarLayout EAST • button);

• Display it (give it a size and make it visible)

Panel A

A layout manageris aJava object associated

with a particular component, almostalwaysa

b ackgroun dcomponent, The layout manager

controls the components containedwithin the

component the layout manager is associated

with, In other words, ifa frame holds a panel,

and the panel holds a button,the panel's layout

manager controls the size and placement of

the button, while the frame's layout manager

controls the size and placement ofthe _IIIIII!IIII!!!II -~~ ,

panel The button on the other hand

doesn't need a layout manager because the

button isn't holding other components

Ifa panel holds five things even ifthose

five things each have their own layout

managers, the size and location of the five

thingsin the panel are all controlled by the

panel's layout manager.Ifthose five things,

intum,holdotherthings, thea those other

things are placed according to the layout

manager of the thing holding them

When we sayholdwe really mean addas in, a

oanel holdsa button because the buttonwas

addedto the panel using something like:

~Panel.add(button);

Layou t managers come in several flavors, and

each background component can have its own

yo u tmanager.Layout managers have their

wnpolicies to follow when building alayout,

For example, one layout manager might insist

thatall components in a panel must be the same

size,arranged inagrid,while another layout

manager might let each component chooseits

own size, butSlack them vertically.Here's an

exampleof nested layouts:

JPanel panelA =new JPanel () ;

JPanel panelB =new JPanel() ;

layout managers

How does the layout tttat1ager decide?

Different layout managers have different policies for arranging

components (like,arrange in a grid make themall the same size,

stack them vertically, etc.) but the components being layed out do

get at leastsomesmall say in the matter In general, the process of

laying out a background component looks something like this:

@) Add the panel to a frame

@ The frame's layout manager asks the panel how big the panel

prefers to be

@ The panel's layout monager uses its layout policies to decide

whetheritshould respect all, part, or none of the buttons'

everything vertically

<D Make a panel and add three buttons to it

@ The panel's layout manager asks each button-how big

that button prefers to be,

A layout scenario:

@ The frame's layout manager uses its layout policies to decide

whether it should respect all,part, or none of the panel's

preferences

Some layout managers respect the size the componentwants to

be.Ifthe button wants to be 30 pixels by 50 pixels, that's what the

layout manager allocates for that button,Other layout managers

respect only part of the component'spreferred size Ifthe button

wants to be 30 pixels by 50 pixels, it'll be 30 pixels by however

wide the button's backgroundpanel is, Still other layout managers

respect the preference of only the largestof the components

being layed out,and the rest of the components in that panel

are all made that same size.Insome cases, the work of the layout

manager can get very complex, but most of the time you can

figure out what the layout manager will probably do, once you get

to know that layout manager's policies

Ihe Jig fhree layout tttat1agers:

border; flo~ and box.

-

BorderLayout

A BorderLayout manager divides a background

component into fiver~ions.Youcanadd only one

component per region toabackground controlled

by a BorderLayout manager.Components laid out

bythis manager usually don't get to have their

preferred size.9orderlayout Isthe default layout

II\Qna~ for Q fromel

FlowLayout

AFlowLayout manager acts kind of like a word

processor, except with components instead of

words.Each component is the size it wants to be,

and they're laid out left to right in the order that

they'readded with ·word-wrap" turned on So

when a component won'ttit horizontally, it drops

to thenext "line" in the layout.FlowLayout Isthe

default layout mo~,. for a pone"

BoxLayout

A BoxLayout manager is like FlowLayout in that

each component gets to have its own size, and

the components are placed in the order in which

they're added But unlike FlowLayout a BoxLayout

manager can stack the components vertically(or

horizontally, but usually we're just concerned with

vertically).It's like a FlowLayout but instead of

having automatic 'component wrapping', you can

insert a Sort of 'component return key' and force

-the components to start a new line

[ J o 0 -.

1\ :§)

you are here) 403

border layout

about five regions:

east, west, north, south, and center

\ -u

Let's add a button to the!!!! region:

import javax swing.* ; t' \Alld.a ,t y.)t\(a¥

import java an *; ~BcKdlYLa'fOlO I' In.r

public class Buttonl

public static void ma.in (Strinq[l argos) I

Buttonl qui = new Buttonl () i

qui-goO;

JFrame frame = new JFrame () ; SVf.C,I 'fJButton button = new JButton ("cliclc me"); ( ' frame qetContentpane () lldd(BorderLayout.EASTI button)i

frame.Betsi~e(200/200);

frame.setVisible(true);

~

How did the BorderLayout manager come up withthis size for the button?

What are the factors the layout manage.r has toconsider?

Why isn'titwider or taller?

Watch what happens when we give

the button more characters•

public void go() (

JFrame frame = new JFrame();

JButton button = new JButton("c1ick like you mean it");

!rame.getConcentPane() a dd (Bo r de r La you t EAST, button);

rllrespectitspreferredwidth But

rdon'tcare howtall it wantsto be:

it's ganna be as tall asthe frame,becausethat's my policy

border layout

Let's try a button in the NORTH region

public void go() (

J~rame frame =new JFrame();

.mutton button '" new .JButton ("There is no spoon ");

frame.getCohtentPane().add(BorderLayouL.~,button);

frame.setSize(200,200);

frame.setVisible(true);

Now let's make the button ask to be ~II!!,

How do we do that? The button is already as wide

as it can ever be-as wide as the frame But we

cantryto make it tallerbygivingita bigger font

JButton button = new mutton ("Click This! ") ; ~ a"'t -to a\\~t.i,~ht Font bigFont = new Font ("serif", Font BOLD, 28); ~oYt,'nt'D\lt.tor-

button.aetFont(bigFont);

frame.getContentPane() add(BorderLayout.NORTB, button);

frame.setSlze(200,200);

frame.setVisible(true);

I thinkrmgettingit ifrm ineesror

west,I getmypreferred widthbut the

height is up tothe layoutmanager And

if rminnorth orsouth, it'sjust the

opposite-I getmypreferred height, but

not width,

But wltst happens

in tlte center region?

The center region gets whatever's leftl

(except in one special case we'll look at later)

public void go ()

JFrame frame new JFrame();

JButton east new JButton("East");

JButton west new JButton("WestH

)JButton north = new JButc:.on("North");

JButton south = new JButton("SouthH

)JButton center = new JButton("CenterH

)frame.getContentPane() add(BorderLayout.&AST, east);

frarne.getContentPane() add(BorderLayout.WEST, west);

frame.getContentPane() add(BorderLayout.NORTH, north);

frame.gec:.ContentPane().add (BorderLayout SOUTH, south);

frame.getContentPane() add(BorderLayout.CENTER, center);

Let's add a panel to the east region:

A JPanel's layout manager is FJowLayout, by default Wnen we add

a panel to a frame, the size and placement of the panel is still

under the BorderLayout manager's control But anytning insidethe

panel(in other words, components added to the panelbycalling

panel add (aComponent»)are under the panel's FfowLayout

manager's control We'll start by putting an empty panel in the fl'"£lme's

east region, and on the next pages we'll add things to the panel.

import javax.8winq.*;

import java.awt.·;

public class Panel1

publio static void main (SuingIl llrgs) (

Panell qui: new Panel1();

frame getContantpane () add (BorderLayout EAST, panel);

frams.setsize(200,200)i frame.setVisible(true) i

public void go() {

Jframe frame = new Jframe();

JPanel panel = new JPanel();

panel.setBackground(Color.darkGray);

Let's add a button to the panel

th aYlt:\ aYld add-tht:Add t,hf~ 1:.0 e YCll'le\'sla'fOl>t ar.d~('f"

Cll'le\ t.o t.'ne~ya",e -r-:~.!- a dt.ht:~ya",e)s

JButton button'" new JButton ("shock me"); rHo ,) l-Ot'Ihols the'0)" hols -I:'neyaYlel

flow layout

What happens if we add TWO buttons

to the panel?

public void go ()

JFrame frame new JFrame();

JPanel panel new JPanel();

panel.setBackground(Color.darkGray);

-rwD'o \:;\:P sJButton button = new JButton ("shock me"); ~ ,.jjy.e

JButton buttonTwo = new JButton("bliss"); V

panel add (button) ; - ' - -addB

panel add (buttonTwo) ;~ OT»to thl!: rand

frame.getContentPane() add (BorderLayout.EAST, panel);

~en your penCil

If the code above were modified to the code below,

what would the GUllook like?

JButton button = new JButton("shock me");

JButton buttonTwo = new JButton("bliss");

JButton buttonThree = new JButton("huh?H);

think the GUI would

to put them side by side.

Unlike FlowLayout, BoxLayout can force a

'new line' to make the components wrap to

the next line, even If there's room for them

to fit horizontally.

But now you'llhave to change the panel's layout mancger from the

default FlowLayout to BoxLayout

panel) ;

JButton button =- new JButton("shock me");

Jautton buttonTwo = new Jautt.on("bliss");

public void got) {

JFrame frame = new JFrame(l ; a,.a~C" to~a~

JPanel panel = new JPanel () ; C\\a e-t\oIe \a'fO'l"t

t-panel setBackground (Color.darkGr:~iY\S~~ J 'rJo" u~o~

panel.s8tLsyout(new BoxLayout(panel, BoxLayout.Y_AXIS»;

~T n~ Bo~yovttoMb-illk-th~ to"'POhbltif;sI ' huds toknow

vertildl~lH ~ we lASe Y_AXI~ +~ a

you are here ~ 411

layout managers

Q: How come you can't add directlytoa frame the way

you can to a panel?

meets the road In making something appear on the screen.

has to connect to the underlyl ng OS In order to accessthe

is the window frame and the content pane Isthe glass.You

pane with your own JPanel,to make your JPanel the frame's

content pane, using,

myFrama •etcontantpane(myPanel);

Q : can I change the layout manager of the frame?

What If I want the frame to use ftow Instead of border1

A:The easiest way to do this Is to make a panel, build

the GUI the way you want In the panel, and then make that

panel the frame's content pane using the code In the

prevl-ous answer (rather than using the default content pane).

Q : What If I want a different preferred size? Is there a

setSlzeO method for components1

A : Yes, there Is a setSlzeO, but the layout managers will

the component and the size you wa nt It to be.The preferred

(the component makes that decision for Itself) The layout

manager calls the component's getPreferredSlzeO method,

setSlzeO on the component.

Q:can't IJust put things where I want them? can I tum

the layout managers off?

A:vep.on a component by component basis,you can call

the exact screen locations and dimensions In the long run,

though, It's almost always easier to use layout managers.

• Layout managers control the size and location ofcomponents nested within other components

• When you add a component toanother component(sometimes referred10as abackground cornporent

but that's not a technical distinction), the addedcomponent is controlled bythe layout manager ofthe

backgroundcomponenl

• Alayout manager asks components for their

preferred size, before making a decision aboutthe layout Depending on the layout manager'spolicies,it might respect atl, some, or none ofthecomponent's wishes

• The BorderLayout manager lets you add acomponenttoone offive regions You must specifythe regionwhenyou add the component, using thefollowing syntax:

add (BorderLayout EAST, panel);

• WrthBordertayout, components in the north and

Components In the east and west get their preferredwidth, but not height The component in the centergets whatever isleff over (unless you usepack () ).

• The pack() method Is like shrink-wrap for thecomponents;Ituses the full preferred size ofthecenter component, then determines the size oftheframe using the center as a starting point, buildingthe rest based on what's in the other regions

• FlowLayout places components left to right toptobottom, In the order they were added, wrapping toanew line ofcomponents only when the componentswon't fit horizontally

• RowLayout gives components their preferred size inboth dimensions

• BoxLayout lets you align components stackedvertically, evenIfthey could fit side-by-sida UkeFlowLayout BoxLayout uses the preferred size ofthe component inboth dimensions

• BorderLayout isthe default layout manager for aframe; FlowLayout Isthe default for a panel

• Ifyou want a paneltouse something other than flow,you havetocall setLayout () on the panel

Playit1Q with Swittg colitpottettts

You've learned the basics of layout managers, so now let'stryout a

few of the most common components: a text field,scrolling text area,

checkbox, and list, We won't show you the wholedarn API for each of

these, just a few highlights to get you started

JText:F1&1d field % n_ JTex.tField(20); ~e ~.,rl ~'t\d

J'TextField field: new JTAXtFi8ld(~Your nameff)i

• Get an ActionEvent when the user VOlAl,dll alSol'e~isk f

presses return or enter rtally'N.1l'1tiD htara~t~iY evel'lh ityOlA

l/.1tt- P'r't:~s dkty I everyti e thefiald.addActionLiataner(myActionListener) i

• Select/Highlight the textin the field

fiald.aelectAll();

• Put the cursor back in the field (so the user

can just start typing)field requeatFocua () ;

youare here ~ 413

How to use It

• Makeit have a vertical scroll bar only

text area

JTextArea

Unlike JTextField, JTextArea can have more than one line of text It

takes Q little configuration to make one, because it doesn't come out of

the box with scroll bars or line wrappi"9.Tomake a J'TextAr'e(] scroll , you

have to stick it in a ScroliPane A ScroJiPane isanobject that r'e(]11y loves

to scroll and will take care of the text ereo's scrolli"9 needs '- \o \)

text.lIetLineWrap(true);~ T",,"II 01\line ~affi~ f a~st\"ollba\" l&SC Oftysc:roller.aetvertiea1Sc:rol1BarPolicy(ScrollPaneConlitants.VERTlCAL SCROLLBAR AL~IIcroller.set8orizonta1Sc:rol1BarPolicy(Sc:rollPaneConatants.BORIZONTAL_SCROLLBAR_NEVER);

• Append to the text that's in it

taxt.append("button cliakedH

)

• Select/Highlight thetext inthe field

taxt.lIelectAll();

• Put the cursor back inthe field(so the user

can just start typing)

text.requelltFocua() ;

public void go() (

JFrame frame - new JFrame();

JPanel panel = new JPanel () ;

JButton button::; new JButton("Just Click It");

button addActionListener (this) ;

text::; new JTaxtArea(lO,20);

text.setLinewrap(true);

}

public static void main (String [] &rqs)

TextAreal qui c new TextAreal();

qui.go () ;

public class TaxtAreal implements ActionL~staner{

import jaYaX.swing.*;

import java.art.*;

import java.art.event.*;

JScrollPane scrollar ~ new JScrollPane{taxt);

scroller.setVerticalScrolLBarPolicy(ScrollPaneConstants.VERTICAL_SCROLLBAR_AL~YS);scrollar.setBorizontalScrollBarPolicy(ScrollPaneConstants.80RIZONTAL_SCROLLBAR_NEVER);panel add (scroller) ;

frame qetContentpane(l add(BorderLayout.CENTER, panel);

frame qetContentpane () add (BordarLayout.SOO'TB, button);

Handle the event (and find out whether or not it's selected)

public void itemstateChanged(ItemEvent ev)

String onOrOff ="off";

if (check.isSelected(» onOrOff ="on";

System.out.println("Check box is " + onOrOff);

, Select or deselect it in code

check.setSelected(true);

check.setSelected(false);

O th UUlDere1atE}{l?~uesti9ns"

Q: Aren't the layout ers just more trouble than they'reworth? If I have to go to all thistrouble, I might as well just hard-code the size and coordinates forwhere everything should go

manag-A: Getting the exact layout you want from a layout man- ager can be a challenge But think about what the layout manager

is really doing for you Eventhe seemingly simple task of figuring out where things should go on the screen can be complex For example , the layout manager takes care of keeping your components from overlapping one another

In other words, it knows how to manage the spacing between components (and between the edge of the frame) Sure you can

do that yourself, but what happens

if you want components to be very tightly packed? You might get them placed just right, by hand, but that's only good for your JVM! Why? Because the components can be slightly different from platform to platform, especially if they use the underly ing platform 's

native 'look and fee 1/ , Subtle things like the bevel of the buttons can

be different in such a way that components that line up neatly

on one platform suddenly squish together on another

And we 're still not at the really Big Thing that layout managers do Think about what happens when the user resizesthe window! Or your GUI is dynamic, where com- ponents come and go If you had

to keep track of re-Iaying out all the components every time there 's

a change in the size or contents of

a background component yikes!

Constructor

String [] H.atEntries '" ("a lpha", "beta", \'ga:nmta", "delta",

"apailon", "zeta", "eta H

, "theta "I;

list.addListSelectionListenar(this);

list'" new JLlst(liatEntrie.);

How to use It

• Make it have a vertical scrollbar

JSerollPane acroller '" new JScrolIPane(liat) ;

scroller.setVerticalScrol~Poliey(ScroIIPaneConstanta.VERTlCAL_SCROLL8AR_ALMAYS); acroller.setaorizontalScrollBarPolicy(ScrollPan8Constants.HORIZONTAL_SCROLLBAR_NEVER); panel.add(acroller);

Set the number of lines to show before scrolling

• Handle events (find out which thing in the list wasselected~ / fllt.j" this i~ test.

public void va.lueChanqed (ListselectionEvent lse) (E;"

String selecUon " (String) list getSelectedValue0 ; ~eiSdttudV~lueOad:. I~

rcwn.sa"Objett, Alisti 'f.li iud toOYII"/oL.~U"'''5• 0b:,)etu.' S:.

you are here. 417

Code Kitchen

This part's optional We're ~ing the lull BeatBox, GUI and all In the Saving Objects chapter, we'll learn how to

save and restore drum patterns FinallyI in the networlung

Makit1Q the JeatJox

This is the full code listing for this version of the BeatBox, with buttons for starting,

stopping, and changing the tempo.The code listing is complete,and

fully-annotated, but here's the overview:

•

•

•

•

Build a GUI that has 256 checkboxes (JCheckBox) that start out

unchecked, 16 labels (JLabel) for the instrument names, and four

buttons

Register an ActionListener for each of the four buttons We don't

need listeners for the individual checkboxes, because we aren't

trying to change the pattern sound dynamically (i.e.as soon as the

user checks a box) Instead, we wait until the user hits the 'start'

button, and then walk through all 256 checkboxes to get their state

and make a MIDI track

Set-up the MIDI system (you've done this before) including getting

a Sequencer, making a Sequence, and creating a track We are using

a sequencer method that's new to Java 5.0, setLoopCount( ) This

method allows you to specify how many times you want a sequence

to loop We're also using the sequence's tempo factor to adjust the

tempo up or down, and maintain the new tempo from one iteration of

the loop to the next

When the user hits 'start', the real action begins The event-handling

method for the 'start' button calls the buildTrackAndStartO method

In that method, we walk through all 256 checkboxes (one row at

a time, a single instrument across all 16 beats) to get their state,

then use the information to build a MIDI track (using the handy

makeEventO method we used in the previous chapter) Once the track

is built, we start the sequencer, which keeps playing (because we're

looping it) until the user hits 'stop'

you ar e here ~ 419

public elass BeatBox {

~ The'S(dre ~e I\d"'CS ~the i~""LlftIents, dS aShi"

' " an-dY, to'<" bl.tildi"~ t.hc qUIlabels (on eJth 'row) ~

("Bass Drum", "Closed Hi-Bat", Snare", "Crash Cymbal", "Band Clap",

"Maxacas", "Whistle", "Low Conga",

"Low-mid Tom", "High Aqoqo" ,

public static void main (String[] args) {

new BestBox2 () buildGUI (J ;

checkboxList:: new ArrayList<JCheckBox.>() ;

Box buttonBox: new Box(BoxLayout.Y_AXIS);

JButton start c new JButton("Start");

start.addActionListener(new MyStartListener());

buttonBox.add(start) ;

JSutton stop: new JButton("Stop") ;

stop.addActionListener(naw MyStopListaner(»;

buttonBox add (stop) ;

JButton upTempo : new JButton("Tempo CpU);

upTempo.addActionListener(new MyUpTempoListener());

buttonBox,add(upTempo);

JSutton downTempo :: new JButton ("Tempo Down");

downTempo addActionLi s tener(n_ MyDownTempoLis tener () ) ;

buttonBox.add(dovnTempo);

Box nameBox = new Box (80xLayout Y_AX! S) ;

for (int i = 0; i < 16; i++) {

nameBox.add(new Label (i.nst rumentNa.mes [i]» ;

background add (BorderLayout EAST, buttonBox) ;

background add (80rd.erLayout.WEST, namaBox);

theFrame.getcontentpane() add (background) ;

GridLayout grid = new GridLayout(16,16) ;

grid setVgap(1) ;

grid setHqap(2) ;

mainPanel = new JPanel(grid) ;

background add (BorcierLayout CEN"l'ER, mainPanel);

for (int i = 0; i < 256; i++) {

sequence.deleteTrack(track) ;

for (int i = 0; i < 16; i++)

for (int j =0; j < 16; j++ ) { ~ Do this~OV"eath~ theBE.ATS ~OV" thisYOW

trackList [j) = 0; the key vall.lein thisslotin theayyay(the slotthat

} Ye~esents thisbeaV Otheywise, the inshWl'lent is

I I close inner loop NOT slAffosedto flay at this beat, so set it.toUyo·

makeTracks (trackList) ; -,.- :: - roY this i\'\StYWI'Ient., and~OV" all Ibbeats,

track add (makeEvent (176,1,127,0,16) ) ; ",ake eve"ts and add the",tothe hade

public class~ !iI ~ ~ :£! DI ~f Mimplements ActionListener

buildTrackAndStart();

}

public class (mJ.HRa,~g~ implements ActionListener

public void actionPerformed(ActionEvent a) (

sequencer.stop() ;

}

II close inner class

public classr~EtItl=i!iij~jimplements ActionListener

public void actionPerformed(ActionEvent a) (

float tempoFactor =sequencer.getTempoFactor() ;

sequencer.setTempoFactor«float) (tempoFactor * 1.03»;

}

II close inner class

ublic class " '"".c "'! 'T ) " *9i ' :mr ':~ii l implements ActionListener

p :m % ",~ , ' w,~, , "iI , ,, ,, ,,, , ,.A '

public void actionPerformed(ActionEvent a) (

float tempoFactor =sequencer.getTempoFactor();

sequencer.setTempoFactor«float) (tempoFactor * 97 » ;

}

} II close inner class

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public voidlllll.ll~(int[] list)

for (int i =0; i < 16; i++) (

int key =list[i];

i f (key != 0) {

track.add(makeEvent(144,9,key, 100,track.add(makeEvent(128,9,key, 100, ~) ); L Make the NOT~ON a\'\d

1+1»; ) NOT oFFe'le\'\ts a\'\d

add thew>tothe T\'"atk

public MidiEvent~ ~ ,ij ( int comd, int chan,

MidiEvent event =null;

try {

ShortMessage a =new ShortMessage();

a setMessage (comd, chan, one, two);

event =new MidiEvent(a, tick);

exercise: Which Layout?

Which code goes with

Five of the slx screens below were made from one

of the code fragments on the opposite page Match each of the five code fragments with the layout that fragment would produce.

e

code Fragments

panel setBackground (Color darkGray) ;

frame.getContentPane() add(BorderLayout.NORTH,panel);

panel.add(buttonTwo);

frame.getContentPane() add(BorderLayout.CENTER,button);

panel.setBackground(Color.darkGray);

panel.add(buttonTwo) ;

frame.getContentPane() add(BorderLayout.CENTER,button);

frame.getContentPane() add (BorderLayout.EAST, panel);

panel.setBackground(Color.darkGray);

panel.add(buttonTwo);

frame.getContentPane() add(BorderLayout.CENTER,button);

panel setBackground (Color darkGray) ;

panel add (button) ;

frame.getContentPane() add(BorderLayout.NORTH,buttonTwo) ;

frame.getContentPane() add (BorderLayout EAST, panel);

panel setBackground (Color.darkGray) ;

frame.getContentPane() add (BorderLayout SOUTH ,panel) ;

panel.add(buttonTwo) ;

frame.getContentPane() add (BorderLayout.NORTH ,button) ;

you are here; 425