MC LCChng 1: GII THIU TNG QUAN V NGN NG LP TRNH JAVA
.........................................................................
7 1.1. M u
.........................................................................
7 1.2. Gii thiu v ngn ng lp trnh Java............................ 7
1.2.1. Java l g?
.............................................................. 7
1.2.2. Lch s pht trin ca ngn ng lp trnh Java........ 7 1.2.3. Mt s
c im ni bc ca ngn ng lp trnh Java
........................................................................................
8 1.3. Cc ng dng Java
...................................................... 10 1.3.1.
Java v ng dng Console .................................... 10
1.3.2. Java v ng dng Applet ......................................
11 1.3.3. Java v pht trin ng dng Desktop dng AWT v JFC
................................................................................
12 1.3.4. Java v pht trin ng dng Web.......................... 13
1.3.5. Java v pht trin cc ng dng nhng ................. 14 1.4. Dch
v thc thi mt chng trnh vit bng Java........ 14 1.5. Chng trnh Java
u tin.......................................... 15 1.5.1. To chng
trnh ngun HelloWordApp .............. 15 1.5.2. Bin dch tp tin ngun
HelloWordApp................ 16 1.5.3. Chy chng trnh
HelloWordApp....................... 16 1.5.4. Cu trc chng trnh
HelloWordApp.................. 17 S dng phng thc/bin ca
lp................................ 17 1.6. Cng c lp trnh v chng
trnh dch........................ 17 1.6.1. J2SDK
.................................................................
17 1.6.2. Cng c son tho m ngun Java. ....................... 18
Chng 2:
.............................................................................
21 HNG, BIN, KIU D LIU, ...........................................
21 TON T, BIU THC V CC ....................................... 21
CU TRC IU KHIN TRONG JAVA .......................... 21 2.1. Bin
............................................................................
21 2.2. Cc kiu d liu c
s................................................. 23 2.2.1. Kiu s
nguyn .................................................... 24
2.2.2. Kiu du chm ng.............................................
26 1
2.2.3. Kiu k t (char)
.................................................. 26 2.2.4. Kiu
lun l (boolean).......................................... 27 2.3.
Hng:
..........................................................................
27 2.4. Lnh, khi lnh trong
java........................................... 28 2.5. Ton t v biu
thc ................................................... 29 2.5.1.
Ton t s hc...................................................... 29
2.5.2. Ton t trn
bit..................................................... 29 2.5.3.
Ton t quan h & logic ....................................... 29
2.5.4. Ton t p kiu
.................................................... 30 2.5.5. Ton
t iu kin ................................................. 30
2.5.6. Th t u tin
...................................................... 30 2.6. Cu
trc iu khin .....................................................
31 2.6.1. Cu trc iu kin if else .................................
31 2.6.2. Cu trc switch case
........................................ 32 2.6.3. Cu trc
lp.......................................................... 32
2.6.4. Cu trc lnh nhy (jump) ....................................
33 2.7. Lp bao kiu d liu c s (Wrapper Class)................ 33
2.8. Kiu d liu
mng....................................................... 34
2.8.1. Khi nim mng
................................................... 34 2.8.2. Khai
bo mng ..................................................... 34
2.8.3. Cp pht b nh cho mng ................................... 35
2.8.4. Khi to
mng...................................................... 35 2.8.5.
Truy cp mng .....................................................
35 2.9. Mt s v d minh ha:
............................................... 36 Chng 3: HNG I
TNG TRONG JAVA ............... 47 3.1. M u
.......................................................................
47 3.2. Lp (Class)
.................................................................
48 3.2.1. Khi nim
............................................................ 48
3.2.2. Khai bo/nh ngha lp .......................................
48 3.2.3. To i tng ca lp ..........................................
49 3.2.4. Thuc tnh ca lp
............................................... 49 3.2.5. Hm - Phng
thc lp (Method)......................... 50 3.2.6. Khi to mt i tng
(Constructor)................... 52 3.2.7. Bin
this...............................................................
53 2
3.2.8. Khai bo chng phng thc (overloading method)
......................................................................................
54 3.3. c im hng i tng trong java ......................... 54
3.3.1. ng gi (encapsulation) .....................................
55 3.3.2. Tnh a hnh (polymorphism): ..............................
55 3.3.3. Tnh k tha (inheritance)
.................................... 57 3.4. Gi (packages)
............................................................ 62
3.5. Giao din (interface)
................................................... 63 3.5.1. Khi
nim interface: ............................................. 63
3.5.2. Khai bo interface:
............................................... 64 3.5.3. V d minh
ha..................................................... 65 Chng 4:
THIT K GIAO DIN NGI DNG............. 82 4.1. M u
.......................................................................
82 4.2. Gii thiu th vin
awt................................................ 83 4.3. Cc khi
nim c bn.................................................. 83
4.3.1.
Component...........................................................
83 4.3.2. Container
............................................................. 84
4.3.3. Layout Manager
................................................... 85 4.4. Thit k
GUI cho chng trnh ................................... 86 4.4.1. To
khung cha ca s chng trnh .................... 86 4.4.2. To h thng
thc n.......................................... 87 4.4.3. Gn
Component vo khung cha.......................... 89 4.4.4. Trnh by
cc Component trong khung cha ........ 90 4.4.5. Cc i tng khung cha
Container.................. 101 4.5. X l bin c/s kin
................................................ 105 4.5.1. M hnh x
l s kin (Event-Handling Model) . 105 4.5.2. X l s kin chut
............................................ 108 4.5.3. X l s kin
bn phm ...................................... 111 4.6. Mt s v d
minh ha .............................................. 115 Chng 5:
LUNG V TP TIN....................................... 128 5.1. M u
.....................................................................
128 5.2. Lung (Streams)
....................................................... 129 5.2.1.
Khi nim lung................................................. 129
5.2.2. Lung byte (Byte Streams).................................
129 5.2.3. Lung k t (Character Streams)........................ 131
3
5.2.4. Nhng lung c nh ngha trc (The Predefined Streams)
......................................................................
132 5.3. S dng lung Byte
.................................................. 133 5.3.1. c d
liu t Console....................................... 134 5.3.2. Xut
d liu ra Console...................................... 135 5.3.3. c
v ghi file dng lung Byte ......................... 136 5.3.4. c v
ghi d liu nh phn................................ 141 5.4. File truy
cp ngu nhin (Random Access Files) ....... 145 5.5. S dng lung k
t.................................................. 147 5.5.1. Nhp
Console dng lung k t ......................... 149 5.5.2. Xut
Console dng lung k t .......................... 151 5.5.3. c/ghi
File dng lung k t............................ 152 5.6. Lp File
....................................................................
155 Chng 6: LP TRNH C S D LIU.......................... 158 6.1.
GII
THIU.............................................................
158 6.2. KIN TRC
JDBC................................................... 158 6.3. Cc
khi nim c bn................................................ 160
6.3.1. JDBC Driver
...................................................... 160 6.3.2.
JDBC URL ........................................................
162 6.4. KT NI CSDL VI JDBC .....................................
163 6.4.1. ng k trnh iu khin ....................................
163 6.4.2. Thc hin kt ni
............................................... 163 6.4.3. V
d..................................................................
164 6.5. KIU D LIU SQL V KIU D LIU JAVA.... 168 6.6. CC THAO TC C
BN TRN CSDL................ 170 6.6.1. Cc lp c bn
................................................... 170 6.6.2. V d
truy vn CSDL ......................................... 171 6.6.3. V
d cp nht CSDL ......................................... 174 Ti liu
tham
kho:..............................................................
176 Ph lc A: Trc nghim kin
thc........................................ 177 Ph Lc B:p n trc
nghim kin thc............................. 205
4
LI NI UNgn ng lp trnh java ra i v c cc nh nghin cu ca Cng ty Sun
Microsystem gii thiu vo nm 1995. Sau khi ra i khng lu, ngn ng lp
trnh ny c s dng rng ri v ph bin i vi cc lp trnh vin chuyn nghip cng
nh cc nh pht trin phn mm. Gn y ngn ng lp trnh, cng ngh java c a vo
ging dy cc c s o to lp trnh vin chuyn nghip. Mt s trng i hc Vit Nam
dy mn lp trnh java nh mt chuyn t chn cho cc sinh vin cng ngh thng
tin giai on chuyn ngnh. Sau mt thi gian tm hiu, lm vic v c tham gia
ging dy chuyn lp trnh java cho lp c nhn tin hc t xa qua mng. Nhm tc
gi chng ti quyt nh bin son cun gio trnh ny nhm phc v cng tc ging dy
cng nh hc tp ca sinh vin chuyn ngnh cng ngh thng tin. Ni dung gio
trnh tp trung vo nhng kin thc cn bn nht ca lp trnh java gip ngi c
bc u tip cp d dng vi cng ngh mi ny, v y cng chnh l mt bc m chng ta
tr thnh java shooter. Mt s vn nng trong ngn ng lp trnh java nh:
javabean, thit kt giao din dng th vin JFC(Java Foundation Class),
lp trnh mng, lp trnh c s d liu bng java, lp trnh ng dng web dng
J2EE (Java 2 Enterprise Edition), s c ni n trong cc chuyn nng cao.
Chng 6 ca gio trnh gii thiu tng quan v lp trnh c s d liu dng jdbc,
mt ni dung theo chng ti cn phi c trnh by trong mt chuyn ring. c th
c hiu gio trnh ny ngi c cn nm vng cc kin thc v: nhp mn lp trnh, lp
trnh hng i tng. y l ln xut bn u tin chc chn khng th trnh khi nhng
sai st. Nhm tc gi rt mong nhn c nhng kin ng gp ca qu thy c, cc ng
nghip v bn c c 5
th hon thin hn gio trnh ny phc v cho vic hc tp ca sinh vin. Xin
chn thnh cm n! TPHCM thng 01/2006 Nhm tc gi
6
Chng 1: GII THIU TNG QUAN V NGN NG LP TRNH JAVA1.1.M u Chng ny s
cung cp cho sinh vin cc khi nim, kin thc c bn lin quan n vic lp
trnh ng dng bng ngn ng Java nh: lch s pht trin ca java, cc c im ca
java, khi nim my o, cu trc ca mt chng trnh n gin vit bng Java cng
nh cch xy dng, dch v thc thi mt chng trnh Java. 1.2.Gii thiu v ngn
ng lp trnh Java 1.2.1. Java l g? Java l ngn ng lp trnh hng i tng
(ta C++) do Sun Microsystem a ra vo gia thp nin 90. Chng trnh vit
bng ngn ng lp trnh java c th chy trn bt k h thng no c ci my o java
(Java Virtual Machine). 1.2.2.Lch s pht trin ca ngn ng lp trnh Java
Ngn ng lp trnh Java do James Gosling v cc cng s ca Cng ty Sun
Microsystem pht trin. u thp nin 90, Sun Microsystem tp hp cc nh
nghin cu thnh lp nn nhm t tn l Green Team. Nhm Green Team c trch
nhim xy dng cng ngh mi cho ngnh in t tiu dng. gii quyt vn ny nhm
nghin cu pht trin xy dng mt ngn ng lp trnh mi t tn l Oak tng t nh
C++ nhng loi b mt s tnh nng nguy him ca C++ v c kh nng chy trn nhiu
nn phn cng khc nhau. Cng lc world wide web bt u pht trin v Sun thy
c tim nng ca ngn ng Oak nn u t ci tin
7
v pht trin. Sau khng lu ngn ng mi vi tn gi l Java ra i v c gii
thiu nm 1995. Java l tn gi ca mt hn o Indonexia, y l ni nhm nghin
cu pht trin chn t tn cho ngn ng lp trnh Java trong mt chuyn i tham
quan v lm vic trn hn o ny. Hn o Java ny l ni rt ni ting vi nhiu khu
vn trng cafe, chnh l l do chng ta thng thy biu tng ly caf trong
nhiu sn phm phn mm, cng c lp trnh Java ca Sun cng nh mt s hng phn
mm khc a ra. 1.2.3.Mt s c im ni bc ca ngn ng lp trnh Java My o Java
(JVM - Java Virtual Machine) Tt c cc chng trnh mun thc thi c th phi
c bin dch ra m my. M my ca tng kin trc CPU ca mi my tnh l khc nhau
(tp lnh m my ca CPU Intel, CPU Solarix, CPU Macintosh l khc nhau),
v vy trc y mt chng trnh sau khi c bin dch xong ch c th chy c trn mt
kin trc CPU c th no . i vi CPU Intel chng ta c th chy cc h iu hnh
nh Microsoft Windows, Unix, Linux, OS/2, Chng trnh thc thi c trn
Windows c bin dch di dng file c ui .EXE cn trn Linux th c bin dch
di dng file c ui .ELF, v vy trc y mt chng trnh chy c trn Windows
mun chy c trn h iu hnh khc nh Linux chng hn th phi chnh sa v bin
dch li. Ngn ng lp trnh Java ra i, nh vo my o Java m kh khn nu trn c
khc phc. Mt chng trnh vit bng ngn ng lp trnh Java s c bin dch ra m
ca my o java (m java bytecode). Sau my o Java chu trch nhim chuyn m
java bytecode thnh m my tng ng. Sun Microsystem chu trch nhim pht
trin cc my o Java chy trn cc h iu hnh trn cc kin trc CPU khc nhau.
Thng dch: 8
Java l mt ngn ng lp trnh va bin dch va thng dch. Chng trnh ngun
vit bng ngn ng lp trnh Java c ui *.java u tin c bin dch thnh tp tin
c ui *.class v sau s c trnh thng dch thng dch thnh m my. c lp nn:
Mt chng trnh vit bng ngn ng Java c th chy trn nhiu my tnh c h iu
hnh khc nhau (Windows, Unix, Linux, ) min sao c ci t my o java
(Java Virtual Machine). Vit mt ln chy mi ni (write once run
anywhere). Hng i tng: Hng i tng trong Java tng t nh C++ nhng Java l
mt ngn ng lp trnh hng i tng hon ton. Tt c mi th cp n trong Java u
lin quan n cc i tng c nh ngha trc, thm ch hm chnh ca mt chng trnh
vit bng Java ( l hm main) cng phi t bn trong mt lp. Hng i tng trong
Java khng c tnh a k tha (multi inheritance) nh trong C++ m thay vo
Java a ra khi nim interface h tr tnh a k tha. Vn ny s c bn chi tit
trong chng 3. a nhim - a lung (MultiTasking - Multithreading): Java
h tr lp trnh a nhim, a lung cho php nhiu tin trnh, tiu trnh c th
chy song song cng mt thi im v tng tc vi nhau. Kh chuyn (portable):
Chng trnh ng dng vit bng ngn ng Java ch cn chy c trn my o Java l c
th chy c trn bt k my tnh, h iu hnh no c my o Java. Vit mt ln, chy
mi ni (Write Once, Run Anywhere). H tr mnh cho vic pht trin ng dng:
9
Cng ngh Java pht trin mnh m nh vo i gia Sun Microsystem cung cp
nhiu cng c, th vin lp trnh phong ph h tr cho vic pht trin nhiu loi
hnh ng dng khc nhau c th nh: J2SE (Java 2 Standard Edition) h tr
pht trin nhng ng dng n, ng dng client-server; J2EE (Java 2
Enterprise Edition) h tr pht trin cc ng dng thng mi, J2ME (Java 2
Micro Edition) h tr pht trin cc ng dng trn cc thit b di ng, khng
dy, 1.3.Cc ng dng Java 1.3.1.Java v ng dng Console ng dng Console l
ng dng nhp xut ch vn bn tng t nh mn hnh Console ca h iu hnh MS-DOS.
Lai chng trnh ng dng ny thch hp vi nhng ai bc u lm quen vi ngn ng
lp trnh java. Cc ng dng kiu Console thng c dng minh ha cc v d c bn
lin quan n c php ngn ng, cc thut ton, v cc chng trnh ng dng khng cn
thit n giao din ngi dng ha.
class HelloWorld { public static void main(String[] args) 10
{ System.out.println("\nHello World"); } } 1.3.2.Java v ng dng
Applet Java Applet l loi ng dng c th nhng v chy trong trang web ca
mt trnh duyt web. T khi internet mi ra i, Java Applet cung cp mt kh
nng lp trnh mnh m cho cc trang web. Nhng gn y khi cc chng trnh duyt
web pht trin vi kh nng lp trnh bng VB Script, Java Script, HTML,
DHTML, XML, cng vi s canh tranh khc lit ca Microsoft v Sun lm cho
Java Applet lu m. V cho n by gi gn nh cc lp trnh vin u khng cn mn m
vi Java Applet na. (trnh duyt IE i km trong phin bn Windows 2000
khng cn mc nhin h tr thc thi mt ng dng Java Applet). Hnh bn di minh
ha mt chng trnh java applet thc thi trong mt trang web.
11
1.3.3.Java v pht trin ng dng Desktop dng AWT v JFC Vic pht trin
cc chng trnh ng dng c giao din ngi dng ha trc quan ging nh nhng
chng trnh c vit dng ngn ng lp trnh VC++ hay Visual Basic c java gii
quyt bng th vin AWT v JFC. JFC l th vin rt phong ph v h tr mnh m hn
nhiu so vi AWT. JFC gip cho ngi lp trnh c th to ra mt giao din trc
quan ca bt k ng dng no. Lin quan n vic pht trin cc ng dng c giao
din ngi dng ha trc quan chng ta s tm hiu chi tit trong chng 4. Minh
ha thit k giao din ngi dng s dng JFC
12
1.3.4.Java v pht trin ng dng Web Java h tr mnh m i vi vic pht
trin cc ng dng Web thng qua cng ngh J2EE (Java 2 Enterprise
Edition). Cng ngh J2EE hon ton c th to ra cc ng dng Web mt cch hiu
qu khng thua km cng ngh .NET m Microsft ang qung co. Hin nay c rt
nhiu trang Web ni ting Vit Nam cng nh khp ni trn th gii c xy dng v
pht trin da trn nn cng ngh Java. S ng dng Web c xy dng dng cng ngh
Java chc chn khng ai c th bit c con s chnh xc l bao nhiu, nhng chng
ti a ra y vi v d thy rng cng ngh Java ca Sun l mt i th ng gm ca
Microsoft. 13
http://java.sun.com/ http://e-docs.bea.com/
http://www.macromedia.com/software/jrun/
http://tomcat.apache.org/index.html Chc khng t ngi trong chng ta
bit n trang web thng tin nh t ni ting TPHCM l:
http://www.nhadat.com/. ng dng Web ny cng c xy dng da trn nn cng
ngh java. Bn c th tm hiu chi tit hn v cng ngh J2EE to a ch:
http://java.sun.com/j2ee/ 1.3.5.Java v pht trin cc ng dng nhng Java
Sun a ra cng ngh J2ME (The Java 2 Platform, Micro Edition J2ME) h
tr pht trin cc chng trnh, phn mm nhng. J2ME cung cp mt mi trng cho
nhng chng trnh ng dng c th chy c trn cc thit b c nhn nh: in thai di
ng, my tnh b ti PDA hay Palm, cng nh cc thit b nhng khc.
Bn c th tm hiu chi tit hn v cng ngh J2ME ti a ch:
http://java.sun.com/j2me/ 1.4.Dch v thc thi mt chng trnh vit bng
Java Vic xy dng, dch v thc thi mt chng trnh vit bng ngn ng lp trnh
java c th tm tt qua cc bc sau: - Vit m ngun: dng mt chng trnh son
tho no y (NotePad hay Jcreator chng hn) vit m ngun v lu li vi tn c
ui .java 14
-
-
Bin dch ra m my o: dng trnh bin dch javac bin dch m ngun .java
thnh m ca my o (java bytecode) c ui .class v lu ln a Thng dch v thc
thi: ng dng c load vo b nh, thng dch v thc thi dng trnh thng dch
Java thng qua lnh java. o a m java bytecode vo b nh: y l bc
loading. Chng trnh phi c t vo trong b nh trc khi thc thi. Loader s
ly cc files cha m java bytecode c ui .class v np chng vo b nh. o
Kim tra m java bytecode: trc khi trnh thng dch chuyn m bytecode
thnh m my tng ng thc thi th cc m bytecode phi c kim tra tnh hp l. o
Thng dch & thc thi: cui cng di s iu khin ca CPU v trnh thng dch
ti mi thi im s c mt m bytecode c chuyn sang m my v thc thi.
1.5.Chng trnh Java u tin 1.5.1.To chng trnh ngun HelloWordApp
Khi ng Notepad v g on m sau /*Vit chng trnh in dng HelloWorld ln mn
hnh Console*/ class HelloWorldApp{ public static void main(String[]
args){ //In dong chu HelloWorld System.out.println(HelloWorld); } }
Lu li vi tn HelloWorldApp.java 15
1.5.2.Bin dch tp tin ngun HelloWordApp Vic bin dch tp tin m ngun
chng trnh HelloWorldApp c th thc hin qua cc bc c th nh sau: - M ca
s Command Prompt. - Chuyn n th mc cha tp tin ngun va to ra. - Thc
hin cu lnh: javac HelloWordApp.java Nu gp thng bo li Bad Command of
filename hoc The name specified is not recognized as an internal or
external command, operable program or batch file c ngha l Windows
khng tm c trnh bin dch javac. sa li ny chng ta cn cp nht li ng dn
PATH ca h thng. Ngc li nu thnh cng bn s c thm tp tin
HelloWordApp.class 1.5.3.Chy chng trnh HelloWordApp Ti du nhc g
lnh: java HelloWordApp Nu chng trnh ng bn s thy dng ch HelloWord
trn mn hnh Console. Nu cc bn nhn c li Exception in thread "main
java.lang.NoClassDefFoundError: HelloWorldApp c ngha l Java khng th
tm c tp tin m bytecode tn HelloWorldApp.class ca cc bn. Mt trong
nhng ni java c tm tp tin bytecode l th mc hin ti ca
16
cc bn. V th nu tp tin byte code c t C:\java th cc bn nn thay i
ng dn ti . 1.5.4.Cu trc chng trnh HelloWordApp Phng thc main(): l
im bt u thc thi mt ng dng. Mi ng dng Java phi cha mt phng thc main
c dng nh sau: public static void main(String[] args) Phng thc main
cha ba b t c t sau: public ch ra rng phng thc main c th c gi bi bt
k i tng no. static ch ra rng phng thc main l mt phng thc lp. void
ch ra rng phng thc main s khng tr v bt k mt gi tr no. Ngn ng Java h
tr ba kiu ch thch sau: /* text */ // text /** documentation */. Cng
c javadoc trong b JDK s dng ch thch ny chun b cho vic t ng pht sinh
ti liu. - Du m v ng ngo8c nhn { v }: l bt u v kt thc 1 khi lnh. -
Du chm phy ; kt thc 1 dng lnh. 1.5.5.S dng phng thc/bin ca lp C
php: Tn_lp.Tn_bin hoc Tn_lp.Tn_phng_thc() 1.6.Cng c lp trnh v chng
trnh dch 1.6.1.J2SDK Download J2SE phin bn mi nht tng ng vi h iu
hnh ang s dng t a ch java.sun.com v ci 17
t ln my tnh (phin bn c chng ti s dng khi vit gio trnh ny l J2SE
1.4). Sau khi ci xong, chng ta cn cp nht ng dn PATH h thng ch n th
mc cha chng trnh dch ca ngn ng java.
1.6.2.Cng c son tho m ngun Java. vit m ngun java chng ta c th s
dng trnh son tho NotePad hoc mt s mi trng pht trin h tr ngn ng java
nh: Jbuilder ca hng Borland, Visual Caf ca hng Symantec, JDeveloper
ca hng Oracle, Visual J++ ca Microsoft, Trong khun kh gio trnh ny
cng nh hng dn sinh vin thc hnh chng ti dng cng c JCreator LE v3.50
ca hng XINOX Software. Cc bn c th download JCreator LE v3.50 t
http://www.jcreator.com/download.htm. V d: Dng JCreator to v thc
thi chng trnh c tn HelloWorldApp. Bc 1: To 1 Empty Project 18
-
File New Project. Chn Empty project ri bm nt chn Next
-
Sau nhp tn project v bm chn Finish.
Bc 2: To mt Class mi tn HelloWorldApp v a vo Project hin ti. -
File New Class. - Nhp vo tn Class v chn Finish (hnh bn di).
19
Bc 3: Son tho m ngun (hnh bn di)Dch (F7)
Thc thi (F5)
Ca s WorkSpace
Ca s son tho m ngun
20
Chng 2: HNG, BIN, KIU D LIU, TON T, BIU THC V CC CU TRC IU KHIN
TRONG JAVA2.1.Bin Bin l vng nh dng lu tr cc gi tr ca chng trnh. Mi
bin gn lin vi mt kiu d liu v mt nh danh duy nht gi l tn bin. - Tn
bin thng thng l mt chui cc k t (Unicode), k s. o Tn bin phi bt u
bng mt ch ci, mt du gch di hay du dollar. o Tn bin khng c trng vi
cc t kha (xem ph lc cc t kha trong java). o Tn bin khng c khong
trng gia tn. - Trong java, bin c th c khai bo bt k ni u trong chng
trnh. Cch khai bo ; = ; Gn gi tr cho bin = ; Bin cng cng (ton cc):
l bin c th truy xut khp ni trong chng trnh, thng c khai bo dng t
kha public, hoc t chng trong mt class. Bin cc b: l bin ch c th truy
xut trong khi lnh n khai bo.
21
Lu : Trong ngn ng lp trnh java c phn bit ch in hoa v in thng. V
vy chng ta cn lu khi t tn cho cc i tng d liu cng nh cc x l trong
chng trnh. V d: import java.lang.*; import java.io.*; class
VariableDemo { static int x, y; public static void main(String[]
args) { x = 10; y = 20; int z = x+y; System.out.println("x = " +
x); System.out.println("y = " + y); System.out.println("z = x + y
=" + z); System.out.println("So nho hon la so:" + Math.min(x, y));
char c = 80; System.out.println("ky tu c la: " + c); } } Kt qu chng
trnh
22
2.2.Cc kiu d liu c s Ngn ng lp trnh java c 8 kiu d liu c s:
byte, short, int, long, float, double, boolean v char.
23
Kiu c s
Kiu lun l
Kiu k t kiu nguyn
Kiu s kiu thc
boolean
char
byte
short
int
long
float
double
Kiu
byte short int long float double
Kch thc (bytes) 1 2 4 8 4 8
Gi tr min
Gi tr max
-256 -32768 -231 -263
255 32767 231 - 1 263 - 1
Gi tr mc nh 0 0 0 0L 0.0f 0.0d
2.2.1.Kiu s nguyn Java cung cp 4 kiu s nguyn khc nhau l: byte,
short, int, long. Kch thc, gi tr nh nht, ln nht, cng nh gi tr mc nh
ca cc kiu d liu s nguyn c m t chi tit trong bng trn. Kiu mc nh ca
cc s nguyn l kiu int. Cc s nguyn kiu byte v short rt t khi c dng.
Trong java khng c kiu s nguyn khng du nh trong ngn ng C/C++. 24
-
Khai bo v khi to gi tr cho cc bin kiu nguyn: int x = 0; long y =
100; Mt s lu i vi cc php ton trn s nguyn: - Nu hai ton hng kiu long
th kt qu l kiu long. Mt trong hai ton hng khng phi kiu long s c
chuyn thnh kiu long trc khi thc hin php ton. - Nu hai ton hng u
khng phi kiu long th php tnh s thc hin vi kiu int. - Cc ton hng kiu
byte hay short s c chuyn sang kiu int trc khi thc hin php ton. -
Trong java khng th chuyn bin kiu int v kiu boolean nh trong ngn ng
C/C++. V d: c on chng trnh nh sau boolean b = false; if (b == 0) {
System.out.println("Xin chao"); } Lc bin dch on chng trnh trn trnh
dch s bo li: khng c php so snh bin kiu boolean vi mt gi tr kiu
int.
25
2.2.2.Kiu du chm ng i vi kiu du chm ng hay kiu thc, java h tr
hai kiu d liu l float v double. Kiu float c kch thc 4 byte v gi tr
mc nh l 0.0f Kiu double c kch thc 8 byte v gi tr mc nh l 0.0d S kiu
du chm ng khng c gi tr nh nht cng khng c gi tr ln nht. Chng c th
nhn cc gi tr: - S m - S dng - V cc m - V cc dng Khai bo v khi to gi
tr cho cc bin kiu du chm ng: float x = 100.0/7; double y = 1.56E6;
Mt s lu i vi cc php ton trn s du chm ng: - Nu mi ton hng u c kiu dn
chm ng th php ton chuyn thnh php ton du chm ng. - Nu c mt ton hng l
double th cc ton hng cn li s c chuyn thnh kiu double trc khi thc
hin php ton. - Bin kiu float v double c th p chuyn sang kiu d liu
khc tr kiu boolean. 2.2.3.Kiu k t (char) Kiu k t trong ngn ng lp
trnh java c kch thc l 2 bytes v ch dng biu din cc k t trong b m
Unicode. Nh vy kiu char trong java c th biu din tt c 216 = 65536 k
t khc nhau. Gi tr mc nh cho mt bin kiu char l null.
26
2.2.4.Kiu lun l (boolean) Kiu boolean ch nhn 1 trong 2 gi tr:
true hoc false. Trong java kiu boolean khng th chuyn thnh kiu nguyn
v ngc li. Gi tr mc nh ca kiu boolean l false.
2.3.Hng: Hng l mt gi tr bt bin trong chng trnh Tn hng c t theo
qui c ging nh tn bin. Hng s nguyn: trng hp gi tr hng dng long ta
thm vo cui chui s ch l hay L. (v d: 1L) Hng s thc: trung hp gi tr
hng c kiu float ta thm tip v ng f hay F, cn kiu s double th ta thm
tip v ng d hay D. Hng Boolean: java c 2 hng boolean l true, false.
Hng k t: l mt k t n nm gia nm gia 2 du ngoc n. o V d: a: hng k t a
o Mt s hng k t c bit
-
K t \b \t \n \r \ \ \\ \f \uxxxx
ngha Xa li (BackSpace) Tab Xung hng Du enter Nhy kp Nhy n S ngc
y trang K t unicode
27
-
Hng chui: l tp hp cc k t c t gia hai du nhy kp . Mt hng chui
khng c k t no l mt hng chui rng. o V d: Hello Wolrd o Lu : Hng chui
khng phi l mt kiu d liu c s nhng vn c khai bo v s dng trong cc chng
trnh.
2.4.Lnh, khi lnh trong java Ging nh trong ngn ng C, cc cu lnh
trong java kt thc bng mt du chm phy (;). Mt khi lnh l on chng trnh
gm hai lnh tr ln v c bt u bng du m ngoc nhn ({) v kt thc bng du ng
ngoc nhc (}). Bn trong mt khi lnh c th cha mt hay nhiu lnh hoc cha
cc khi lnh khc. { // khi 1 { // khi 2 lnh 2.1 lnh 2.2 } // kt thc
khi lnh 2 lnh 1.1 lnh 1.2 } // kt thc khi lnh 1 { // bt u khi lnh 3
// Cc lnh thuc khi lnh 3 // } // kt thc thi lnh 3
28
2.5.Ton t v biu thc 2.5.1.Ton t s hc Ton t + * / % ++ - ngha Cng
Tr Nhn Chia nguyn Chia d Tng 1 Gim 1
2.5.2.Ton t trn bit Ton t & | ^ > >>> ~ ngha AND
OR XOR Dch tri Dch phi Dch phi v in 0 vo bit trng B bit
2.5.3.Ton t quan h & logic Ton t == != > < >= Nu iu
kin ng th c gi tr, hay thc hin , cn ngc li l . : l mt biu thc logic
, : c th l hai gi tr, hai biu thc hoc hai hnh ng. V d: int x = 10;
int y = 20; int Z = (x> > == & ^ | && || ?: = Thp
nht
[] -/ >>> (dch phi vin 0 vo bit trng)
. ~ % = !=
max) max = nums[i]; } System.out.println("min and max: " + min +
" " + max); } } class MinMax2 38
{ public static void main(String args[]) { int nums[] = { 99,
-10, 100123, 18, -978, 5623, 463, -9, 287, 49 }; int min, max; min
= max = nums[0]; for(int i=1; i < 10; i++) { if(nums[i] <
min) min = nums[i]; if(nums[i] > max) max = nums[i]; }
System.out.println("Min and max: " + min + " " + max); } }
V d 5: chng trnh minh ha mt li tham chiu n phn t bn ngoi (vut
qu) kch thc mng. class ArrayErr { public static void main(String
args[]) { int sample[] = new int[10]; int i; for(i = 0; i < 100;
i = i+1) sample[i] = i; } }
39
V d 6: Sp xp mng dng phng php sp xp ni bt (Bubble Sort) class
BubbleSort { public static void main(String args[]) { int nums[] =
{ 99, -10, 100123, 18, -978, 5623, 463, -9, 287, 49 }; int a, b, t;
int size; size = 10; // number of elements to sort // display
original array System.out.print("Original array is:"); for(int i=0;
i < size; i++) System.out.print(" " + nums[i]);
System.out.println(); // This is the Bubble sort. for(a=1; a <
size; a++) for(b=size-1; b >= a; b--) { if(nums[b-1] >
nums[b]) { // if out of order // exchange elements t = nums[b-1];
nums[b-1] = nums[b]; nums[b] = t; } } // display sorted array
40
System.out.print("Sorted array is:"); for(int i=0; i < size;
i++) System.out.print(" " + nums[i]); System.out.println(); } }
V d 7: Nhp v xut gi tr ca cc phn t trong mt mng hai chiu. class
TwoD_Arr { public static void main(String args[]) { int t, i; int
table[][] = new int[3][4]; for(t=0; t < 3; ++t) { for(i=0; i
< 4; ++i) { table[t][i] = (t*4)+i+1;
System.out.print(table[t][i] + " "); } System.out.println(); } }
}
41
V d 8: To i tng chui class StringDemo { public static void
main(String args[]) { // Tao chuoi bang nhieu cach khac nhau String
str1 = new String("Chuoi trong java la nhung Objects."); String
str2 = "Chung duoc xay dung bang nhieu cach khac nhau."; String
str3 = new String(str2); System.out.println(str1);
System.out.println(str2); System.out.println(str3); } }
V d 9: Minh ha mt s thao tc c bn trn chui // Chuong trinh minh
hoa cac thao tac tren chuoi ky tu class StrOps { public static void
main(String args[]) { String str1 = "Java la chon lua so mot cho
lap trinh ung dung Web."; String str2 = new String(str1); String
str3 = "Java ho tro doi tuong String de xu ly chuoi"; 42
int result, idx; char ch; System.out.println("str1:" + str1);
System.out.println("str2:" + str2); System.out.println("str3:" +
str3); System.out.println("Chieu dai cua chuoi str1 la: " +
str1.length()); // Hien thi chuoi str1, moi lan mot ky tu.
System.out.println(); for(int i=0; i < str1.length(); i++)
System.out.print(str1.charAt(i)); System.out.println();
if(str1.equals(str2)) System.out.println("str1 == str2"); else
System.out.println("str1 != str2"); if(str1.equals(str3))
System.out.println("str1 == str3"); else System.out.println("str1
!= str3"); result = str1.compareTo(str3); if(result == 0)
System.out.println("str1 = str3 "); else if(result < 0)
System.out.println("str1 < str3"); else System.out.println("str1
> str3"); 43
// Tao chuoi moi cho str4 String str4 = "Mot Hai Ba Mot"; idx =
str4.indexOf("Mot"); System.out.println("str4:" + str4);
System.out.println("Vi tri xuat hien dau tien cua chuoi con 'Mot'
trong str4: " + idx); idx = str4.lastIndexOf("Mot");
System.out.println("Vi tri xuat hien sau cung cua chuoi con 'Mot'
trong str4:" + idx); } }
V d 10: chng trnh nhp vo mt chui v in ra chui nghch o ca chui
nhp. import java.lang.String; import java.io.*; public class
InverstString { public static void main(String arg[]) {
System.out.println("\n *** CHUONG TRINH IN CHUOI NGUOC *** "); try
44
{
System.out.println("\n *** Nhap chuoi:"); BufferedReader in =
new BufferedReader(new InputStreamReader(System.in)); // Class
BufferedReader cho php c text t lung nhp k t, to b m cho nhng k t h
tr cho vic c nhng k t, nhng mng hay nhng dng. // Doc 1 dong tu
BufferReadered ket thuc bang dau ket thuc dong. String str =
in.readLine(); System.out.println("\n Chuoi vua nhap la:" + str);
// Xuat chuoi nghich dao System.out.println("\n Chuoi nghich dao
la:"); for (int i=str.length()-1; i>=0; i--) {
System.out.print(str.charAt(i)); }
} catch (IOException e) { System.out.println(e.toString()); } }
}
V d 11: Ly chui con ca mt chui class SubStr { public static void
main(String args[]) { 45
String orgstr = "Mot Hai Ba Bon"; // Lay chuoi con dung ham //
public String substring(int beginIndex, int // endIndex) String
substr = orgstr.substring(4, 7); System.out.println("Chuoi goc: " +
orgstr); System.out.println("Chuoi con: " + substr); } }
V d 12: Mng cc chui class StringArray { public static void
main(String args[]) { String str[] = {"Mot", "Hai", "Ba", "Bon" };
System.out.print("Mang goc: "); for(int i=0; i < str.length;
i++) System.out.print(str[i] + " "); System.out.println("\n"); //
Thay doi chuoi str[0] = "Bon"; str[1] = "Ba"; str[2] = "Hai";
str[3] = "Mot"; System.out.print("Mang thay doi:"); for(int i=0; i
< str.length; i++) System.out.print(str[i] + " "); 46
System.out.print("\n"); } }
Chng 3: HNG I TNG TRONG JAVA3.1.M u Thng qua chuyn lp trnh hng i
tng (OOP) chng ta bit OOP l mt trong nhng tip cn mnh m, v 47
rt hiu qu xy dng nn nhng chng trnh ng dng trn my tnh. T khi ra i
cho n nay lp trnh OOP chng t c sc mnh, vai tr ca n trong cc n tin
hc. Chng h ny s gip bn c tm hiu v cc kiu d liu dn xut l lp (class)
v giao tip (interface), cng nh cc vn c bn v lp trnh hng i tng trong
java thng qua vic to lp cc lp, cc i tng v cc tnh cht ca chng.
3.2.Lp (Class) 3.2.1.Khi nim Chng ta c th xem lp nh mt khun mu
(template) ca i tng (Object). Trong bao gm d liu ca i tng (fields
hay properties) v cc phng thc(methods) tc ng ln thnh phn d liu gi l
cc phng thc ca lp. Cc i tng c xy dng bi cc lp nn c gi l cc th hin
ca lp (class instance). 3.2.2.Khai bo/nh ngha lp class { ; ;
constructor method_1 method_2 } class: l t kha ca java ClassName: l
tn chng ta t cho lp field_1, field_2: cc thuc tnh, cc bin, hay cc
thnh phn d liu ca lp. constructor: l s xy dng, khi to i tng lp.
method_1, method_2: l cc phng thc/hm th hin cc thao tc x l, tc ng
ln cc thnh phn d liu ca lp. 48
3.2.3.To i tng ca lp ClassName objectName = new ClassName();
3.2.4.Thuc tnh ca lp Vng d liu (fields) hay thuc tnh (properties)
ca lp c khai bo bn trong lp nh sau: class { // khai bo nhng thuc
tnh ca lp field1; // } xc nh quyn truy xut ca cc i tng khc i vi vng
d liu ca lp ngi ta thng dng 3 tin t sau: public: c th truy xut t tt
c cc i tng khc private: mt lp khng th truy xut vng private ca 1 lp
khc. protected: vng protected ca 1 lp ch cho php bn thn lp v nhng
lp dn xut t lp truy cp n. V d: public class xemay { public public
private protected
String String float int
nhasx; model; chiphisx; thoigiansx;
// so luong so cua xe may: 3, 4 so protected int so; // sobanhxe
l bin tnh c gi tr l 2 trong tt c // cc th hin to ra t lp xemay
49
public static }
int
sobanhxe = 2;
Thuc tnh nhasx, modelc th c truy cp n t tt c cc i tng khc. Thuc
tnh chiphisx ch c th truy cp c t cc i tng c kiu xemay Thuc tnh
thoigiansx, so c th truy cp c t cc i tng c kiu xemay v cc i tng ca
cc lp con dn xut t lp xemay Lu : Thng thng an ton cho vng d liu ca
cc i tng ngi ta trnh dng tin t public, m thng chn tin t private ngn
cn quyn truy cp n vng d liu ca mt lp t cc phng thc bn ngoi lp .
3.2.5.Hm - Phng thc lp (Method) Hm hay phng thc (method) trong Java
l khi lnh thc hin cc chc nng, cc hnh vi x l ca lp ln vng d liu.
Khai bo phng thc: () { ; } xc nh quyn truy xut ca cc i tng khc i vi
cc phng thc ca lp ngi ta thng dng cc tin t sau: public: phng thc c
th truy cp c t bn ngoi lp khai bo. protected: c th truy cp c t lp
khai bo v nhng lp dn xut t n. private: ch c truy cp bn trong bn thn
lp khai bo. 50
static: phng thc lp dng chung cho tt c cc th hin ca lp, c ngha l
phng thc c th c thc hin k c khi khng c i tng ca lp cha phng thc .
final: phng thc c tin t ny khng c khai bo chng cc lp dn xut.
abstract: phng thc khng cn ci t (khng c phn source code), s c hin
thc trong cc lp dn xut t lp ny. synchoronized: dng ngn cc tc ng ca
cc i tng khc ln i tng ang xt trong khi ang ng b ha. Dng trong lp
trnh miltithreads. : c th l kiu void, kiu c s hay mt lp. : t theo
qui c ging tn bin. : c th rng Lu : Thng thng trong mt lp cc phng
thc nn c khai bo dng t kha public, khc vi vng d liu thng l dng tin
t private v mc ch an ton. Nhng bin nm trong mt phng thc ca lp l cc
bin cc b (local) v nn c khia to sau khi khai bo. V d: public class
xemay { public public private protected
String String float int
nhasx; model; chiphisx; thoigiansx;
// so luong so cua xe may: 3, 4 so protected int so;
51
// l bin tnh c gi tr l 2 trong tt c // cc th hin to ra t lp
xemay public static int sobanhxe = 2; public float tinhgiaban() {
return 1.5 * chiphisx; } } 3.2.6.Khi to mt i tng (Constructor)
Contructor tht ra l mt loi phng thc c bit ca lp. Constructor dng gi
t ng khi khi to mt th hin ca lp, c th dng khi gn nhng gi tr mc nh.
Cc constructor khng c gi tr tr v, v c th c tham s hoc khng c tham
s. Constructor phi c cng tn vi lp v c gi n dng t kha new. Nu mt lp
khng c constructor th java s cung cp cho lp mt constructor mc nh
(default constructor). Nhng thuc tnh, bin ca lp s c khi to bi cc gi
tr mc nh (s: thng l gi tr 0, kiu lun l l gi tr false, kiu i tng gi
tr null, ) Lu : thng thng an ton, d kim sot v lm ch m ngun chng
trnh chng ta nn khai bo mt constructor cho lp.
V d: public class xemay { // public xemay() 52
{} public xemay(String s_nhasx, String s_model, f_chiphisx, int
i_thoigiansx, int i_so); { nhasx = s_nhasx; model = s_model;
chiphisx = f_chiphisx; thoigiansx = i_thoigiansx; so = i_so; // hoc
// this.nhasx = s_nhasx; // this.model = s_model; // this.chiphisx
= f_chiphisx; // this.thoigiansx = i_thoigiansx; // this.so = i_so;
} } 3.2.7.Bin this Bin this l mt bin n tn ti trong tt c cc lp trong
ngng ng java. Mt class trong Java lun tn ti mt bin this, bin this c
s dng trong khi chy v tham kho n bn thn lp cha n. V d: class A {
int ; String ; // Contructor ca lp A public A(int par_1, String
par_2) { 53
this.field_1 = par_1; this.field_2 = par_2; } () { // } () {
this.method_1() // } } 3.2.8.Khai bo chng phng thc (overloading
method) Vic khai bo trong mt lp nhiu phng thc c cng tn nhng khc
tham s (khc kiu d liu, khc s lng tham s) gi l khai bo chng phng thc
(overloading method). V d: public class xemay { // khai bo fields
public float tinhgiaban() { return 2 * chiphisx; } public float
tinhgiaban(float huehong) { return (2 * chiphisx + huehong); } }
3.3.c im hng i tng trong java H tr nhng nguyn tc c bn ca lp trnh
hng i tng, tt c cc ngn ng lp trnh k c java u c ba c 54
im chung: tnh ng gi (encapsulation), tnh a hnh (polymorphism), v
tnh k tha (inheritance). 3.3.1.ng gi (encapsulation) C ch ng gi
trong lp trnh hng i tng gip cho cc i tng du i mt phn cc chi tit ci
t, cng nh phn d liu cc b ca n, v ch cng b ra ngoi nhng g cn cng b
trao i vi cc i tng khc. Hay chng ta c th ni i tng l mt thnh t h tr
tnh ng gi. n v ng gi c bn ca ngn ng java l class. Mt class nh ngha
hnh thc ca mt i tng. Mt class nh r nhng thnh phn d liu v cc on m ci
t cc thao tc x l trn cc i tng d liu . Java dng class xy dng nhng i
tng. Nhng i tng l nhng th hin (instances) ca mt class. Mt lp bao gm
thnh phn d liu v thnh phn x l. Thnh phn d liu ca mt lp thng bao gm
cc bin thnh vin v cc bin th hin ca lp. Thnh phn x l l cc thao tc
trn cc thnh phn d liu, thng trong java ngi gi l phng thc. Phng thc
l mt thut ng hng i tng trong java, trong C/C++ ngi ta thng dng thut
ng l hm. 3.3.2.Tnh a hnh (polymorphism): Tnh a hnh cho php ci t cc
lp dn xut khc nhau t mt lp ngun. Mt i tng c th c nhiu kiu khc nhau
gi l tnh a hnh. V d: class A_Object { // void method_1() { //
55
} } class B_Object extends A_Object { // void method_1() { // }
} class C { public static void main(String[] args) { // To mt mng 2
phn t kiu A A_Object arr_Object = new A_Object[2]; B_Object var_1 =
new B_Object(); // Phn t u tin ca mng arr_Object[0] tham // chiu n
1 i tng kiu B_Object dn xut // t A_Object arr_Object[0] = var_1;
A_Object var_2; for (int i=0; i= 0 ? circleRadius:0 ); } // Ly bn
knh ca ng trn 68
public double getRadius() { return radius; } // Tnh din tch ng
trn Circle public double area() { return Math.PI * radius * radius;
} // Biu din ng trn bng mt chui public String toString() { return
"Center = " + super.toString() + "; Radius = " + radius; } // tr v
tn ca shape public String getName() { return "Circle"; } } // end
class Circle Lp Circle dn xut t lp Point, mt ng trn c th tch l 0.0,
v vy phng thc volume() ca lp cha khng khai bo chng, n s tha k t lp
Point, m lp Point th tha k t lp Shape. Din tch ng trn khc vi mt im,
v vy phng thc tnh din tch area() c khai bo chng. Phng thc getName()
hin thc phng thc tru tng khai bo trong lp cha, nu phng thc
getName() khng khai bo trong lp Circle th n s k tha t lp Point.
Phng thc setRadius dng gn mt bn knh (radius) mi cho mt
69
i tng ng trn, cn phng thc getRadius tr v bn knh ca mt i tng ng
trn. // nh ngha lp hnh tr Cylinder // trong tp tin Cylinder.java.
public class Cylinder extends Circle { // chiu cao ca Cylinder
protected double height; // constructor khng c tham s public
Cylinder() { // ngm gi n constructor ca lp cha setHeight( 0 ); } //
constructor c tham s public Cylinder( double cylinderHeight, double
cylinderRadius, int xCoordinate, int yCoordinate ) { // Gi
constructor ca lp cha super( cylinderRadius, xCoordinate,
yCoordinate ); setHeight( cylinderHeight ); } // Gn chiu cao cho
Cylinder public void setHeight( double cylinderHeight ) { height =
( cylinderHeight >= 0 ? cylinderHeight :0 ); } 70
// Ly chiu cao ca Cylinder public double getHeight() { return
height; } // Tnh din tch xung quanh ca Cylinder public double
area() { return 2 * super.area() + 2 * Math.PI * radius * height; }
// Tnh th tch ca Cylinder public double volume() { return
super.area() * height; } // Biu din Cylinder bng mt chui public
String toString() { return super.toString() + "; Height = " +
height; } // tr v tn ca shape public String getName() { return
"Cylinder"; } } // end class Cylinder
71
Lp Cylinder dn xut t lp Circle. Mt Cylinder (hnh tr) c din tch v
th tch khc vi mt Circle (hnh trn), v vy c hai phng thc area() v
volume() cn phi khai bo chng. Phng thc getName() l hin thc phng thc
tru tng trong lp cha, nu phng thc getName() khng khai bo trong lp
Cylinder th n s k tha t lp Circle. Phng thc setHeight dng gn chiu
cao mi cho mt i tng hnh tr, cn phng thc getHeight tr v chiu cao ca
mt i tng hnh tr. // Test.java // Kim tra tnh k tha ca Point,
Circle, Cylinder vi // lp tru tng Shape. // Khai bo th vin import
java.text.DecimalFormat; public class Test { // Kim tra tnh k tha
ca cc i tng hnh hc public static void main( String args[] ) { // To
ra cc i tng hnhhc Point point = new Point( 7, 11 ); Circle circle =
new Circle( 3.5, 22, 8 ); Cylinder cylinder = new Cylinder( 10,
3.3, 10, 10 ); // To mt mng cc i tng hnh hc Shape arrayOfShapes[] =
new Shape[ 3 ]; // arrayOfShapes[ 0 ] l mt i tng Point
arrayOfShapes[ 0 ] = point; // arrayOfShapes[ 1 ] l mt i tng Circle
arrayOfShapes[ 1 ] = circle; // arrayOfShapes[ 2 ] l mt i tng
cylinder arrayOfShapes[ 2 ] = cylinder; // Ly tn v biu din ca mi i
tng hnh hc 72
String output = point.getName() + ": " + point.toString() + "\n"
+ circle.getName() + ": " + circle.toString() + "\n" +
cylinder.getName() + ": " + cylinder.toString(); DecimalFormat
precision2 = new DecimalFormat( "0.00" ); // duyt mng arrayOfShapes
ly tn, din tch, th tch // ca mi i tng hnh hc trong mng. for ( int i
= 0; i < arrayOfShapes.length; i++ ) { output += "\n\n" +
arrayOfShapes[ i ].getName() + ": " + arrayOfShapes[ i].toString()
+ "\n Area = " + precision2.format( arrayOfShapes[ i ].area() ) +
"\nVolume = " + precision2.format( arrayOfShapes[ i ].volume() ); }
System.out.println(output); System.exit( 0 ); } } // end class Test
Kt qu thc thi chng trnh:
73
V d 2: Tng t v d 1 nhng trong v d 2 chng ta dng interface nh
ngha cho Shape thay v mt lp tru tng. V vy tt c cc phng thc trong
interface Shape phi c hin thc trong lp Point l lp ci t trc tip
interface Shape. // nh ngha mt interface Shape trong tp tin
shape.java public interface Shape { // Tnh din tch public abstract
double area(); // Tnh th tch public abstract double volume(); // tr
v tn ca shape public abstract String getName(); } Lp Point ci t/hin
thc interface tn shape. // nh ngha lp Point trong tp tin Point.java
public class Point extends Object implements Shape { protected int
x, y; // Ta x, y ca 1 im // constructor khng tham s. public Point()
{ setPoint( 0, 0 ); } // constructor c tham s. public Point(int
xCoordinate, int yCoordinate) { setPoint( xCoordinate, yCoordinate
); 74
} // gn ta x, y cho 1 im public void setPoint( int xCoordinate,
int yCoordinate ) { x = xCoordinate; y = yCoordinate; } // ly ta x
ca 1 im public int getX() { return x; } // ly ta y ca 1 im public
int getY() { return y; } // Th hin ta ca 1 im di dng chui public
String toString() { return "[" + x + ", " + y + "]"; } // Tnh din
tch public double area() { return 0.0; } // Tnh th tch public
double volume() 75
{ return 0.0; } // tr v tn ca i tng shape public String
getName() { return "Point"; } } // end class Point Lp Circle l lp
con ca lp Point, v ci t/hin thc gin tip interface tn shape. // nh
ngha lp Circle trong tp tin Circle.java public class Circle extends
Point { // Dn xut t lpPoint protected double radius; // constructor
khng tham s public Circle() { // ngm gi n constructor ca lp cha
setRadius( 0 ); } // constructor c tham s public Circle( double
circleRadius, int xCoordinate, int yCoordinate ) { // gi
constructorca lp cha super( xCoordinate, yCoordinate ); setRadius(
circleRadius ); } 76
// Gn bn knh ca ng trn public void setRadius( double
circleRadius ) { radius = ( circleRadius >= 0 ? circleRadius:0
); } // Ly bn knh ca ng trn public double getRadius() { return
radius; } // Tnh din tch ng trn Circle public double area() {
return Math.PI * radius * radius; } // Biu din ng trn bng mt chui
public String toString() { return "Center = " + super.toString() +
"; Radius = " + radius; } // tr v tn ca shape public String
getName() { return "Circle"; } } // end class Circle // nh ngha lp
hnh tr Cylinder // trong tp tin Cylinder.java. 77
public class Cylinder extends Circle { // chiu cao ca Cylinder
protected double height; // constructor khng c tham s public
Cylinder() { // ngm gi n constructor ca lp cha setHeight( 0 ); } //
constructor c tham s public Cylinder( double cylinderHeight, double
cylinderRadius, int xCoordinate, int yCoordinate ) { // Gi
constructor ca lp cha super( cylinderRadius, xCoordinate,
yCoordinate ); setHeight( cylinderHeight ); } // Gn chiu cao cho
Cylinder public void setHeight( double cylinderHeight ) { height =
( cylinderHeight >= 0 ? cylinderHeight :0 ); } // Ly chiu cao ca
Cylinder public double getHeight() { return height; 78
} // Tnh din tch xung quanh ca Cylinder public double area() {
return 2 * super.area() + 2 * Math.PI * radius * height; } // Tnh
th tch ca Cylinder public double volume() { return super.area() *
height; } // Biu din Cylinder bng mt chui public String toString()
{ return super.toString() + "; Height = " + height; } // tr v tn ca
shape public String getName() { return "Cylinder"; } } // end class
Cylinder // Test.java // Kim tra tnh k tha ca Point, Circle,
Cylinder vi // interface Shape. // Khai bo th vin import
java.text.DecimalFormat; 79
public class Test { // Kim tra tnh k tha ca cc i tng hnh hc
public static void main( String args[] ) { // To ra cc i tng hnhhc
Point point = new Point( 7, 11 ); Circle circle = new Circle( 3.5,
22, 8 ); Cylinder cylinder = new Cylinder( 10, 3.3, 10, 10 ); // To
mt mng cc i tng hnh hc Shape arrayOfShapes[] = new Shape[ 3 ]; //
arrayOfShapes[ 0 ] l mt i tng Point arrayOfShapes[ 0 ] = point; //
arrayOfShapes[ 1 ] l mt i tng Circle arrayOfShapes[ 1 ] = circle;
// arrayOfShapes[ 2 ] l mt i tng cylinder arrayOfShapes[ 2 ] =
cylinder; // Ly tn v biu din ca mi i tng hnh hc String output =
point.getName() + ": " + point.toString() + "\n" + circle.getName()
+ ": " + circle.toString() + "\n" + cylinder.getName() + ": " +
cylinder.toString(); DecimalFormat precision2 = new DecimalFormat(
"0.00" ); // duyt mng arrayOfShapes ly tn, din tch, th tch // ca mi
i tng hnh hc trong mng. for ( int i = 0; i <
arrayOfShapes.length; i++ ) { output += "\n\n" + arrayOfShapes[ i
].getName() + ": " + arrayOfShapes[ i].toString() + 80
"\n Area = " + precision2.format( arrayOfShapes[ i ].area() ) +
"\nVolume = " + precision2.format( arrayOfShapes[ i ].volume() ); }
System.out.println(output); System.exit( 0 ); } } // end class Test
Kt qu thc thi chng trnh:
81
Chng 4: THIT K GIAO DIN NGIDNG4.1.M u Chng ny cung cp cho sinh
vin nhng kin thc c bn xy dng giao din (Graphic User Interface -
GUI) ca chng trnh ng dng bng ngn ng java: Nhng nguyn tc thit k giao
din. Nhng th vin, gi xy dng giao din: gm nhng lp (class), nhng giao
tip (interface) qun l s kin v nhng thnh phn (components) xy dng nn
giao din ngi dng. B qun l trnh by (layout managers) X l s kin
-
Trong khun kh gio trnh lp trnh java cn bn ny chng ti trnh by vic
thit k GUI dng th vin awt (abstract windows toolkit). Vic thit kt
GUI s trc quan, uyn chuyn hn khi chng ta s dng th vin JFC (Java
Foundation Class) s gii c gii thiu trong chuyn java nng cao.
82
4.2.Gii thiu th vin awt Th vin awt l b th vin dng xy dng giao
din ngi dng cho mt chng trnh ng dng c y cc thnh phn c bn nh: Label,
Button, Checkbox, Radiobutton, Choice, List, Text Field, Text Area,
Scrollbar, Menu, Frame Ging nh cc API ca Windows, java cung cp cho
ngi lp trnh th vin awt. Nhng khc vi cc hm API, th vin awt khng ph
thuc h iu hnh. Th vin awt l nn tng, c s gip cho chng ta tip cn vi
th vin m rng JFC hiu qu hn. Cu trc cy phn cp ca tt c nhng lp trong
th vin awt chng ta c th xem chi tit trong ti liu km theo b cng c
j2se (phn API Specification)
4.3.Cc khi nim c bn 4.3.1.Component Component l mt i tng c biu
din ha c hin th trn mn hnh m ngi dng c th tng tc c. Chng 83
hn nh nhng nt nhn (button), nhng checkbox, nhng scrollbar, Lp
Component l mt lp tru tng.java.lang.Object
java.awt.Component 4.3.2.Container Container l i tng vt cha hay
nhng i tng c kh nng qun l v nhm cc i tng khc li. Nhng i tng con
thuc thnh phn awt nh: button, checkbox, radio button, scrollbar,
list, ch s dng c khi ta a n vo khung cha (container). Mt s i tng
container trong Java: Panel: i tng khung cha n gin nht, dng nhm cc
i tng, thnh phn con li. Mt Panel c th cha bn trong mt Panel
khc.java.lang.Object +--java.awt.Component +--java.awt.Container
+--java.awt.Panel
Frame: khung cha Frame l mt ca s window hn hoi mc trn cng bao gm
mt tiu u v mt ng bin (border) nh cc ng dng windows thng thng khc.
Khung cha Frame thng c s dng to ra ca s chnh ca cc ng
dng.java.lang.Object +--java.awt.Component +--java.awt.Container
+--java.awt.Window +--java.awt.Frame
Dialogs: y l mt ca s dng hp hi thoi (ca s dng ny cn c gi l
pop-up window), ca s dng ny thng c dng a ra thng bo, hay dng ly d
liu nhp t ngoi vo thng qua cc i tng, thnh phn trn dialog nh
TextField chng hn. Dialog
84
cng l mt ca s nhng khng y chc nng nh i tng khung cha
Frame.java.lang.Object +--java.awt.Component +--java.awt.Container
+--java.awt.Window +--java.awt.Dialog
ScrollPanes: l mt khung cha tng t khung cha Panel, nhng c thm 2
thanh trt gip ta t chc v xem c cc i tng ln chon nhiu ch trn mn hnh
nh nhng hnh nh hay vn bn nhiu dng.java.lang.Object
+--java.awt.Component +--java.awt.Container
+--java.awt.ScrollPane
4.3.3.Layout Manager Khung cha container nhn cc i tng t bn ngoi
a vo v n phi bit lm th no t chc sp xp ch cho cc i tng . Mi i tng
khung cha u c mt b qun l chu trch nhim thc hin cng vic y l b qun l
trnh by (Layout Manager). Cc b qun l trnh by m th vin AWT cung cp
cho ta bao gm: FlowLayout: Sp xp cc i tng t tri qua phi v t trn
xung di. Cc i tng u gi nguyn kch thc ca mnh. BorderLayout: Cc i tng
c t theo cc ng vin ca khung cha theo cc cnh West, East, South,
North v Center tc ng, Ty, Nam, Bc v Trung tm hay Tri, Phi, Trn, Di
v Gia ty theo cch nhn ca chng ta. GridLayout: To mt khung li v hnh
vi cc bng nhau. Cc i tng s t va kch thc vi
85
tng . Th t sp xp cng t tri qua phi v t trn xung di.
GridBagLayout: Tng t nh GridLayout, cc i tng khung cha cng c a vo
mt li v hnh. Tuy nhin kch thc cc i tng khng nht thit phi va vi 1 m
c th l 2, 3 hay nhiu hn ty theo cc rng buc m ta ch nh thng qua i
tng GridBagConstraint. Null Layout: Cch trnh by t do. i vi cch trnh
by ny ngi lp trnh phi t ng lm tt c t vic nh kch thc ca cc i tng,
cng nh xc nh v tr ca n trn mn hnh. Ta khng ph thuc vo nhng rng buc
ng, ty , nam, bc g c.
4.4.Thit k GUI cho chng trnh 4.4.1.To khung cha ca s chng trnh
Thng thng to ca s chnh cho chng trnh ng dng ta tin hnh cc bc: - To
i tng Frame - Xc nh kch thc ca Frame - Th hin Frame trn mn hnh V d:
import java.awt.*; class FrameDemo { public static void main(String
args[]) { // To i tng khung chaFrame Frame fr = new Frame("My First
Window") ; // Xc nh kch thc, v tr ca Frame fr.setBounds(0, 0, 640,
480); // Hin th Frame 86
fr.setVisible(true); } } Kt qu thc thi chng trnh:
4.4.2.To h thng thc n i vi th vin awt, xy dng h thng thc n cho
chng trnh ng dng chng ta c th dng cc lp MenuBar, Menu, MenuItem,
MenuShortcut.MenuBar
MenuItem Menu
V d: To h thng thc n cho chng trnh Calculator import java.awt.*;
import java.awt.event.*; class Calculator { public static void
main(String[] args) { 87
createMenu(); } private static void createMenu() { // Tao Frame
ung dung final Frame fr = new Frame(); fr.setLayout(new
BorderLayout()); // Tao cac menu bar MenuBar menu = new MenuBar();
Menu menuFile = new Menu("Edit"); MenuItem copyItem = new
MenuItem("Copy Ctrl+C"); MenuItem pasteItem = new MenuItem("Paste
Ctrl+V"); menuFile.add(copyItem); menuFile.add(pasteItem); Menu
menuHelp = new Menu("Help"); MenuItem hTopicItem = new
MenuItem("Help Topics"); MenuItem hAboutItem = new MenuItem("About
Calculator"); menuHelp.add(hTopicItem); menuHelp.addSeparator();
menuHelp.add(hAboutItem); menu.add(menuFile); menu.add(menuHelp);
fr.setMenuBar(menu); fr.setBounds(100, 100, 300, 200);
fr.setTitle("Calculator"); //fr.setResizable(false);
fr.setVisible(true); // x l bin s kin ng ca s ng dng.
fr.addWindowListener( 88
new WindowAdapter() { public void windowClosing(WindowEvent e) {
System.exit(0); } }); } } Kt qu thc thi chng trnh:
4.4.3.Gn Component vo khung cha gn mt thnh phn, mt i tng
component vo mt ca s (khung cha) chng ta dng phng thc add ca i tng
khung cha container. V d: import java.awt.*; class AddDemo { public
static void main(String args[]) { // To i tng khung chaFrame Frame
fr = new Frame("AddDemo App"); // To i tng Component 89
Button buttOk = new Button(OK); // Gn i tng nt nhn vo khung cha
fr.add(buttOk); // Xc nh kch thc, v tr ca Frame fr.setSize(100,
100); // Hin th Frame fr.setVisible(true); } } Kt qu thc thi chng
trnh:
4.4.4.Trnh by cc Component trong khung cha Nh chng ta bit khung
cha container nhn cc i tng t bn ngoi a vo v n phi bit lm th no t
chc sp xp ch cho cc i tng . Mi i tng khung cha u c mt b qun l chu
trch nhim thc hin cng vic y l b qun l trnh by (Layout Manager).
Chng ta s tm hiu chi tit v cc kiu trnh by ca th vin AWT. Interface
LayoutManager nh ngha giao tip cho nhng lp bit c lm th no trnh by
nhng trong nhng containers 4.4.4.1 FlowLayout public class
FlowLayout extends Object 90
implements LayoutManager, Serializable i vi mt container trnh by
theo kiu FlowLayout th: Cc component gn vo c sp xp theo th t t tri
sang phi v t trn xung di. Cc component c kch thc nh mong mun. Nu
chiu rng ca Container khng ch cho cc component th chng t ng to ra
mt dng mi. FlowLayout thng c dng sp xp cc button trong 1 panel.
Chng ta c th iu chnh khong cch gia cc component. V d: import
java.awt.*; import java.lang.Integer; class FlowLayoutDemo { public
static void main(String args[]) { Frame fr = new Frame("FlowLayout
Demo"); fr.setLayout(new FlowLayout()); fr.add(new Button("Red"));
fr.add(new Button("Green")); fr.add(new Button("Blue")); List li =
new List(); for (int i=0; i 3)) {} c. int x = 6; x = ~x; d. Cu b) v
c) ng 44. Biu thc no sau y cho x c gi tr dng: a. int x = -1; x = x
>>> 5; b. int x = -1; x = x >>> 32; c. byte x =
-1; x = x >>> 5; d. int x = -1; x = x >> 5; 45. Biu
thc no sau y hp l a. String x = Hello; int y = 9; x +=y; b. String
x = Hello; int y = 9; x = x + y; c. String x = null; int y = (x !=
null) && (x.length() > 0) ? x.length() : 0; d. Tt c cc
cu trn u ng 46. on m no sau y in ra mn hnh ch Equal: a. 188
int x = 100; float y = 100.0F; if (x == y) {
System.out.println(Equal); } b. Integer x = new Integer(100);
Integer y = new Integer(100); if (x == y) {
System.out.println(Equal); } c. String x = 100; String y = 100; if
(x == y) { System.out.println(Equal); } d. Cu a. v c. ng 47. Cho
bit kt qu sau khi thi hnh chng trnh sau: 1 : public class Short{ 2:
public static void main(String[] args){ 3: StringBuffer s = new
StringBuffer(Hello); 4: if ((s.length() > 5) && 5:
s.append( there).equals(False))) 6: ;//do nothing 7:
System.out.println(value is + s); 8: } 9: } a. Gi tr xut l Hello b.
Li bin dch ti dng 4 v 5 c. Khng c gi tr xut d. Thng bo
NullPointerException 189
48. Cho bit kt qu sau khi thc hin chng trnh sau: 1 : public
class Xor{ 2: public static void main(String[] args){ 3: byte b =
10;//00001010 4: byte c = 15;//00001111 5: b = (byte)(b ^ c); 6:
System.out.println(b contains + b); 7: } 8: } a. Kt qu l: b
contains 10 b. Kt qu l: b contains 5 c. Kt qu l: b contains 250 d.
Kt qu l: b contains 245 49. Cho bit kt qu sau khi bin dch v thi hnh
chng trnh sau: 1 : public class Conditional{ 2: public static void
mai n(String[] args){ 3: int x = 4; 4: System.out.println(value is
+ 5: ((x > 4 ? 99.99 : 9)); 6: } 7: } a. Kt qu l: value is 99.99
b. Kt qu l: value is 9 c. Kt qu l: value is 9.0 d. Li bin dch ti
dng s 5 50. Cho bit kt qu ca on m sau: 1 : int x = 3; int y = 10; 2
: System.out.println(y % x); a. 0 b. 1 c. 2 d. 3 190
51. Chn cu khai bo khng hp l a. String s; b. abstract double d;
c. abstract final double hyperbolCosine(); d. Tt c cc cu trn u ng
52. Chn cu pht biu ng a. Mt lp tru tng khng th cha phng thc final
b. Mt lp final khng th cha cc phng thc tru tng c. C a) v b) u ng d.
C a) v b) u sai 53. Chn cch sa t nht on m sau bin dch ng 3 : final
class Aaa 4: { 5: int xxx; 6: void yyy(){xxx = 1;} 7: } 8: 9: 10 :
class Bbb extends Aaa 11 : { 12 : final Aaa finalRef = new Aaa();
13 : 14 : final void yyy() 15 : { 16 : System.out.println(In method
yyy()); 17 : finalRef.xxx = 12345; 18 : } 19 : } a. Xa t final dng
1 b. Xo t final dng 10 c. Xa t final dng 1 v 10 d. Khng cn phi chnh
sa g
191
54. Chn pht biu ng cho chng trnh sau 1 : class StaticStuff 2: {
3: static int x = 10; 4: 5: static {x += 5;} 6: 7: public static
void main(String args[]) 8: { 9: System.out.pritln(x = + x); 10 : }
11 : 12 : static {x /= 5} 13 : } a. Li bin dch ti dng 5 v 12 bi v
thiu tn phng thc v kiu tr v b. Chng trnh chy v cho kt qu x = 10 c.
Chng trnh chy v cho kt qu x = 15 d. Chng trnh chy v cho kt qu x = 3
55. Chn pht biu ng cho chng trnh sau: 1 : class HasStatic 2: { 3:
private static int x = 100; 4: 5: public static void main(String
args[]) 6: { 7: HasStatic hs1 = new HasStatic(); 8: hs1.x++; 9:
HasStatic hs2 = new HasStatic(); 10 : hs2.x++; 11 : hs1 = new
HasStatic(); 12 : hs1.x++; 13 : HasStatic.x++; 14 :
System.out.println(x = + x); 192
15 : } 16 : } a. Chng trnh chy v cho kt qu x = 102 b. Chng trnh
chy v cho kt qu x = 103 c. Chng trnh chy v cho kt qu x = 104 d. Tt
c cc cu trn u sai 56. Cho on m sau: 1 : class SuperDuper 2: { 3:
void aMethod(){} 4: } 5: 6 : class Sub extends SuperDuper 7: { 8:
void aMethod(){} 9: } Hy chn t kha ch phm vi hp l ng trc aMethod()
dng 8 a. default b. protected c. public d. Tt c cc cu trn u ng 1:
2: 3: 4: 5: 6: 7: 8: on m sau dng cho 2 cu hi tip theo package
abcde; public class Bird{ protected static int referneceCount = 0;
public Bird(){referenceCount++;} protected void fly(){} static int
getRefCount(){return referenceCount;} }
57. Chn pht biu ng cho lp Bird trn v lp Parrot sau: 193
1 : package abcde; 2: 3 : class Parrot extends abcde.Bird{ 4:
public void fly(){ 5: // 6: } 7: public int getRefCount(){ 8:
return referenceCount; 9: } 10 : } a. Li bin dch dng 4 tp tin
Parrot.java v phng thc fly() l protected trong lp cha v lp Bird v
Parrot nm trong cng package b. Li bin dch dng 4 tp tin Parrot.java
v phng thc fly() l protected trong lp cha v public trong lp con. c.
Li bin dch dng 7 tp tin Parrot.java v phng thc getRefCount() l
static trong lp cha. d. Chng trnh bin dch thnh cng nhng s pht sinh
Exception khi chy nu phng thc fly() ca lp Parrot khng c gi 58. Chn
pht biu ng cho lp Bird trn v lp Nightingale sau: 1 : package
singers; 2: 3 : class Nightingale extends abcde.Bird{ 4:
Nightingale(){ refernceCount++;} 5: 6: public static void
main(String args[]){ 7: System.out.print(Before: + refernceCount);
8: Nightingale florence = new Nightingale(); 9:
System.out.print(After: + refernceCount); 10 : florence.fly(); 11 :
} 12 : } 194
a. Kt qu trn mn hnh l: Before: 0 After: 2 b. Kt qu trn mn hnh l:
Before: 0 After: 1 c. Li bin dch dng 4 ca lp Nightingale v khng th
overidde thnh vin static d. Li bin dch dng 10 ca lp Nightingale v
phng thc fly() l protected trong lp cha. 59. Chn pht biu ng a. Ch
kiu d liu c s mi c chuyn i kiu t ng; chuyn i kiu d liu ca bin tham
chiu phi s dng php p kiu b. Ch bin tham chiu mi c chuyn i kiu t ng;
chuyn kiu ca 1 bin kiu c s phi s dng php ton p kiu c. C kiu d liu c
s v kiu tham chiu u c th chuyn i t ng v p kiu d. Php p kiu i vi d
liu s c th cn php kim tra khi thc thi 60. Dng lnh no sau y s khng
th bin dch: 1 : byte b = 5; 2 : char c = 5; 3 : short s = 55; 4 :
int i = 555; 5 : float f = 555.5f; 6 : b = s; 7 : i = c; 8 : if (f
> b) 9: f = i; a. Dng 3 b. Dng 4 c. Dng 5 d. Dng 6 61. Chn dng
pht sinh li khi bin dch 195
1: 2: 3: a. b. c. d.
byte b = 2; byte b1 = 3; b = b * b1; Dng 1 Dng 2 Dng 3 Tt c cc
cu trn u ng
62. Trong on m sau kiu d liu ca bin result c th l nhng kiu no? 1
: byte b = 11; 2 : short s =13; 3 : result = b * ++s; a. byte,
short, int, long, float, double b. boolean, byte, short, char, int,
long, float, double c. byte, short, char, int, long, float, double
d. int, long, float, double 63. Cho on chng trnh sau: 1 : class
Cruncher{ 2: void crunch(int i){ 3: System.out.println(int
version): 4: } 5: void crunch(String s){ 6:
System.out.println(String version); 7: } 8: 9: public static void
main(String[] args){ 10 : Cruncher crun = new Cruncher(); 11 : char
ch = p; 12 : crun.crunch(ch); 13 : } 14 : } a. Dng 5 s khng bin dch
v phng thc tr v kiu void khng th overridde 196
b. Dng 12 s khng bin dch v khng c phin bn no ca phng thc
crunch() nhn vo tham s kiu char c. on m bin dch c nhng s pht sinh
Exception dng 12 d. Chng trnh chy v in ra kt qu: int version 64.
Chn pht biu ng a. Tham chiu ca i tng c th c chuyn i trong php gn
nhng khng th thc hin trong php gi phng thc b. Tham chiu ca i tng c
th c p kiu trong php gi phng thc nhng khng th thc hin trong php gn
c. Tham chiu ca i tng c th c chuyn i trong php gi phng thc v php gn
nhng tun theo nhng quy tc khc nhau d. Tham chiu ca i tng c th c
chuyn i trong php gi phng thc v php gn v tun theo nhng quy tc ging
nhau 65. Cho on m nh bn di. Hy cho bit dng no khng th bin dch 1 :
Object ob = new Object(); 2 : String stringarr[] = new String[50];
3 : Float floater = new Float(3.14f); 4 : ob = stringarr; 5 : ob =
stringarr[5]; 6 : floater = ob; 7 : ob = floater; a. Dng 4 b. Dng 5
a. Dng 6 b. Dng 7
197
Animal
Mammal
Dog
Cat (implements Washer)
Racoon (implements Washer)
Swamp Thing
Hnh sau p dng cho cc cu 66, 67, 68 66. Cho on m sau: 1 :Dog
rover, fido; 2 :Animal anim; 3: 4 :rover = new Dog(); 5 :anim =
rover; 6 :fido = (Dog)anim; Hy chn pht biu ng a. Dng 5 khng th bin
dch b. Dng 6 khng th bin dch c. on m bin dch thnh cng nhng s pht
sinh Exception ti dng 6 d. on m bin dch thnh cng v c th thi hnh 67.
Cho on m sau: 1 :Cat sunflower; 2 :Washer wawa; 3 :SwampThing pogo;
4: 5 :sunflower = new Cat(); 198
6 :wawa = sunflower; 7 :pogo = (SwampThing)wawa; Hy chn pht biu
a. Dng 6 khng th bin dch; cn c mt php p kiu chuyn t kiu Cat sang
kiu Washer b. Dng 7 khng th bin dch v khng th p t kiu interface
sang kiu class c. on m s dch v chy nhng php p kiu dng 7 l tha v c
th b di d. on m bin dch thnh cng nhng s pht sinh Exceptiono dng 7 v
kiu lp ca i tng trong bin wawa lc thi hnh khng th chuyn sang kiu
SwampThing 68. Cho on m sau 1 :Racoon rocky; 2 :SwampThing pogo; 3
:Washer w; 4: 5 :rocky = new Racooon(); 6 :w = rocky; 7 :pogo = w;
a. Dng 6 s khng bin dch; cn phi c php p kiu chuyn t kiu Racoon sang
kiu Washer b. Dng 7 s khng bin dch; cn c php p kiu chuyn t kiu
Washer sang kiu SwampThing c. on m s bin dch nhng s pht sinh
Exception dng 7 v chuyn i kiu khi thc thi t interface sang class l
khng c php d. on m s bin dch v s pht sinh Exception dng 7 v kiu lp
ca w ti thi im thc thi khng th chuyn sang kiu SwampThing 69. Cho on
m sau: 1 : for (int i = 0; i < 2; i++){ 2: for (int j = 0; j
< 3; j++){ 199
3: 4: 5: 6: 7: 8: }
if (i == j){ continue; } System.out.println(i = + i + j = + j);
}
Dng no s l mt trong s cc kt qu c in ra? a. i = 0 j = 0 b. i = 2
j = 1 c. i = 0 j = 2 d. i = 1 j = 1 70. Cho on m sau: 1 : outer:
for (int i = 0; i < 2; i++){ 2: for (int j =0; j < 3; j++){
3: if (i == j){ 4: continue outer; 5: } 6: System.out.println(i = +
i + j = + j); 7: } 8: } Dng no s l mt trong s cc kt qu c in ra? a.
i = 0 j = 0 b. i = 0 j = 1 c. i = 0 j = 2 d. i = 1 j = 0 71. Chn
vng lp ng a. 1 : while (int i < 7){ 2: i++; 3:
System.out.println(i is + i); 4: } b. 200
5: 6: 7: 8: c. 1: 2: 3: 4: d. 1: 2: 3: 4: 5:
int i = 3; while (i){ System.out.println(i is + i); } int j = 0;
for(int k = 0; j + k != 10; j++, k++){ System.out.println(j is + j
+ k is + k); } int j = 0; do{ System.out.println(j is + j++); if (j
== 3) { continue loop;} }while (j < 10);
72. Cho bit kt xut ca on m sau 1 : int x = 0, y = 4, z = 5; 2 :
if ( x > 2){ 3: if (y < 5){ 4: System.out.println(message
one); 5: } 6: else{ 7: System.out.println(message two); 8: } 9: }
10 : else if (z > 5){ 11 : System.out.println(message three); 12
: } 13 : else{ 14 : System.out.println(message four); 15 : } a.
message one b. message two c. message three 201
d. message four 73. Chn pht biu ng cho on m sau: 1 : int j = 2;
2 : switch (j){ 3: case 2: 4: System.out.println(value is two); 5:
case 2 + 1: 6: System.out.println(value is three); 7: break; 8:
default: 9: System.out.println(value is + j); 10 : break; 11 : } a.
on m khng hp l bi biu thc dng 5 b. Bin j trong cu trc switch() c th
l mt trong cc kiu: byte, short, int hoc long c. Kt xut ca chng trnh
ch l dng: value is two d. Kt xut ca chng trnh ch l dng: value is
two v value is three 74. Cho bit kt qu sau khi dch v thc thi on
chng trnh sau: 1. import java.awt.*; 2. 3. public class Test
extends Frame { 4. Test() { 5. setSize(300,300); 6. Button b = new
Button(Apply); 7. add(b); 8. } 9. 10. public static void
main(String args[]) { 11. Test f = new Test(); 12.
f.setVisible(true); 202
13. } 14. } a) C li bin dch ti dng 11 bi v constructor dng 4
khng khai bo public. b) Chng trnh bin dch thnh cng nhng c s nm ra
exception khi thc thi cu lnh dng th 7. c) Chng trnh hin th frame
trng. d) Chng trnh hin th 1 nt nhn (Button) s dng font ch mc nh cho
nhn ca Button. Button ch ln bao quanh nhn ca n. e) Chng trnh hin th
nt nhn (Button) dng font ch mc nh cho nhn nt. Nt nhn s chon tt c
vng hin th ca frame. 75. Nu 1 frame dng b qun l trnh by (layout
manager) l GridLayout v khng cha bt k panel hay container no khc bn
trong n th tt c nhng components khi a vo trong frame ny c cng kch
thc nh nhau (ngang, dc)? a) ng. b) Sai. 76. Nu 1 frame dng b qun l
trnh by (layout manager) mc nh v khng cha bt k panel no bn trong th
tt c nhng components bn trong frame l cng kch thc (ngang, dc) ? a)
ng. b) Sai. 77. Vi b qun l trnh by BorderLayout khng nht thit cc
vng phi c cha cc components. a) ng. b) Sai. 78. B qun l trnh by mc
nh cho 1 khung cha kiu Panel l: 203
a) b) c) d)
FlowLayout BorderLayout GridLayout GridBagLayout
79. Mt Container c b qun l trnh by l GridBagLayout th mi
component s c kch thc bng nhau khi thm vo khung cha (container) ny?
a) ng b) Sai 80. Bn c th to ra ca s chnh ca ng dng bng cch gi:
Frame f = new Frame(Main Frame); Nhng khi bn chy chng trnh th Frame
khng hin th. Dng no bn di s lm hin th Frame. a) f.setSize(300,
200); b) f.setBounds(10, 10, 500, 400); c)
f.setForeground(Color.white); d) f.setVisible(true); 81. i tng no
bn di c th cha 1 menubar (chn nhng cu ng) a) Panel b) ScrollPane c)
Frame d) Menu 82. Sau khi to 1 frame bng cu lnh Frame f = new
Frame() v to menu bar bng cu lnh MenuBar mb = new MenuBar(), lm th
no gn MenuBar tn mb vo f. a) f.add(mb) b) f.setMenu(mb) c)
f.addMenu(mb) d) f.setMenuBar(mb)
204
Ph Lc B: p n trc nghim kin thc1.c; 2.b; 3.d; 4.c; 5.d; 6.d; 7.c;
8.a; 9.d; 10.a; 11.a; 12.c; 14.d; 15.a; 16.d; 17.a; 18.c; 19.a;
20.c; 21.a; 22.a; 23.a; 25.c; 26.a; 27.a; 28.d; 29.d; 30.c; 31.b;
32.a; 33.b; 34.d; 36.c; 37.d; 38.d; 39.c; 40.c; 41.c; 42.c; 43.d;
44.a; 45.d; 47.a; 48.b; 49.c; 50.b; 51.d; 52.b; 53.a; 54.d; 55.c;
56.d; 58.a; 59.c; 60.d; 61.c; 62.d; 63.d; 64.d; 65.c; 66.d; 67.d;
69.c; 70.d; 71.c; 72.d; 73.d; 74.e; 75.a; 76.b; 77.a; 78.a; 80.d;
81.c; 82.d 13.b; 24.a; 35.c; 46.d; 57.c; 68.b; 79.b;
205
