C bn v lp trnh hng i tng trong PHP
Cp nht vo 15:51, ngy 15/02/2014, 799 lt xem, 0 bnh lun
Qua bi hng dn ny, cc bn s tm hiu c cc khi nim ca lp trnh hng i tng trong PHP, cch khi to i tng thng qua mt s v d n gin.
Lp trnh hng i tng l g?
Lp trnh hng i tng c ghi tt l OOP (object-oriented programming). L mt phung hng lp trnh tch bit so vi kiu c in. S dng i tng lp trnh nn nhng chui tung tc. OOP gip cho cc lp trnh vin c th tit kim nhiu thi gian hn so vi cch vit c in.
Cc bn c th hiu lp trnh hng i tng l cch vit m lnh c cc hnh ng lin quan n nhau c nhm thnh cc lp (class) gip tng kh nng rt gn m m vn gi c tnh hiu qu cho chng.
Lp trnh hng i tng khng qu ng s nh mt s bn ngh. Chnh v n c c php mi m v phong cch lp trnh khc bit so vi lp trnh hng th tc nn cc bn thy n phc tp. Nu bn hiu r v bn cht ca lp trnh hng i tng bn s thy lp trnh hng i tng l mt phng php lp trnh n gin m li ti u.
S khc nhau gia lp trnh hng i tng v lp trnh hng cu trc
-Lp trnh hng cu trc: Chia mt chng trnh thnh cc modul gii quyt tng thnh phn ca bi ton (hay cn gi l chia tr). Tch mt vn kh thnh cc vn nh hn d gii quyt. V th phi vit cc hm gii quyt tng modul mt, ri cho php gi ln nhau t mc ch lp trnh.
-Lp trnh hng i tng: S dng cc i tng trong chng trnh, tc l cc lp (class), khi chng trnh s s dng class nh mt kiu d liu nhng do ngi s dng to nn. Lp trnh hng i tng hin ang c u chung do c th s dng li nhng m vit bng vic k tha cc thuc tnh sn c nh vy vic lp trnh t hiu qu cao, tit kim thi gian.
S khc nhau gia lp (class) v i tng(Object)
C nhiu bn cn c s nhm ln gia lp v i tng. Khng ch l nhng bn mi lp trnh m c nhiu lp trnh vin c nhiu nm kinh nghim vn cha phn bit ng v lp v i tng.
phn bit gia class v object cc bn hy ly v d nh bn ang thi cng mt cy cu.
-Class: Tng t nh mt bn kt hoch chi tit cho cy cu. Bn s cn phi xc nh hnh dng ca cy cu, mi quan h gia cc thnh phn ca n(chn cu, thn cu, ko ct,), cc k hoch cho n
-Object: S l mt cy cu c thi cng bi bn k hoch trn. Bn trong Object s cha rt nhiu d liu nh cc vt liu to ra n(si, , nha ng,). V tt nhin, bn s c th xy dng c rt nhiu cy cu t mt bn k hoch nh trn.
CcClassx l cu trc d liu v cc hnh ng, ng thi s dng cc thng tin xy dng ccObject. C th c nhiu hn mtObjectc xy dng t cng mtClassti cng mt thi im, miObjectny u l mt c th c lp v khng ph thuc ln nhau.
Cu trc ca mt Class
Cu trc ca mt class bao gm:thuc tnhvphng thc.
Hiu mt cch n gin ging nh lp trnh hng cu trc:
Trch dn
- Thuc tnh: Cc bin- Phng thc: Cc hm
C php:1
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3Class TnClass{Properties and Method}
- Cc bin trongClassc gi l Properties (Thuc tnh)- Cc hm trongClassc gi l Method (Phng thc)
Sau khi to xongClass, bn c th khi to i tng theo c php sau:C php:1
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nh ngha thuc tnh ca Class
Thuc tnh hot ng nh mt bin thng thng, ch c mt iu l thuc tnh lin kt vi object (i tng). V vy truy cp v s dng c ta phi thng qua object.
C php:1
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-Phm vi: Phm vi c php s dng thuc tnh. Bao gm:public,private,protected,static,... Phm vi c th c, c th khng. Nu khng nh ngha phm vi th phm vi mc nh lpublic
-Tn bin: Tun theo quy tc t tn bin trong PHP
-Gi tr: Gi tr ca thuc tnh.
Lu : Thuc tnh khng nht thit phi gn gi tr ban u.
V d:Bn to 1 file c tnvidu.phpri vit ni dung sau y:
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Cc bn chyhttp://localhost/vidu.phptrnh duyt s hin th kt qu sau:
Trch dn
Welcome to website Giaotrinhcntt.Com
nh ngha phng thc ca class
Tip theo v d trn, cc bn sa code nh sau:
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Lu :Cc i tng c th t tham chiu chnh n bng cch s dng bin $this. Khi lm vic bn trong 1 phng thc, s dng $this cng ging nh cch bn s dng object name bn ngoi class.
Cc nhn vo on code trn cc bn cng bit c cch s dng phng thc. Cch s dng phng thc ging nh cch s dng hm thng thng, nhng chng ta phi thng qua object.
Cc bn chy li filevidu.phps hin th kt qu nh sau:
Trch dn
Welcome to website Giaotrinhcntt.ComHc PHP min ph
Qua bi hc ny, cc bn nm c nhng khi nim v lp trnh hng i tng trong PHP, cch nh ngha lp, thuc tnh, phng thc, khi to i tng, s dng thuc tnh, phng thc.Hn gp li cc bn bi hc tip theo trong series hng dn hc lp trnh php nng cao!
Lp trnh hng i tng l g?
ng bi:Hiu ngNgy ng:25.12.2013Chuyn mc:PHP Nng Cao|Bnh lun :1PHP Nng Cao Sau khi cc bn xem cc bi vit ca mnh trong phn PHP Cn Bn chn cc bn hiu r cc kin thc c bn v Lp Trnh PHP ri ng khng? Hm nay mnh
PHP Nng Cao Sau khi cc bn xem cc bi vit ca mnh trong phnPHP Cn Bnchn cc bn hiu r cc kin thc c bn vLp Trnh PHPri ng khng? Hm nay mnh s gii thiu v hng dn cc bn hiu r v cc kin thc ca lp trnh php nng cao.
Trc tin cc bn d hiu v d tip thu cc bi vit pha sau, th hm nay mnh s gii hiu n cc bn mt khi nim khng cn xa li i vi nhng bn no tng hp lp trnh nhng c l mi m vi nhng bn bc u tm hiu. l khi nim Lp trnh hng i tng l g?
1. Lp trnh hng i tng l?Lp trnh hng i tng (gi tt l OOP, t ch Anh ng object-oriented programming), hay cn gi l lp trnh nh hng i tng, l k thut lp trnh h tr cng ngh i tng. OOP c xem l gip tng nng sut, n gin ha phc tp khi bo tr cng nh m rng phn mm bng cch cho php lp trnh vin tp trung vo cc i tng phn mm bc cao hn. Ngoi ra, nhiu ngi cn cho rng OOP d tip thu hn cho nhng ngi mi hc v lp trnh hn l cc phng php trc .
Mt cch gin lc, y l khi nim v l mt n lc nhm gim nh cc thao tc vit m cho ngi lp trnh, cho php h to ra cc ng dng m cc yu t bn ngoi c th tng tc vi cc chng trnh ging nh l tng tc vi cc i tng vt l.
Nhng i tng trong mt ngn ng OOP l cc kt hp gia m v d liu m chng c nhn nhn nh l mt n v duy nht. Mi i tng c mt tn ring bit v tt c cc tham chiu n i tng c tin hnh qua tn ca n. Nh vy, mi i tng c kh nng nhn vo cc thng bo, x l d liu (bn trong ca n), v gi ra hay tr li n cc i tng khc hay n mi trng.
2. Cc tnh cht c bn ca lp trnh hng i tngi tng (object):Cc d liu v ch th c kt hp vo mt n v y to nn mt i tng. n v ny tng ng vi mt chng trnh con v v th cc i tng s c chia thnh hai b phn chnh: phn cc phng thc (method) v phn cc thuc tnh (property). Trong thc t, cc phng thc ca i tng l cc hm v cc thuc tnh ca n l cc bin, cc tham s hay hng ni ti ca mt i tng (hay ni cch khc tp hp cc d liu ni ti to thnh thuc tnh ca i tng). Cc phng thc l phng tin s dng mt i tng trong khi cc thuc tnh s m t i tng c nhng tnh cht g.
Cc phng thc v cc thuc tnh thng gn cht vi thc t cc c tnh v s dng ca mt i tng.
Trong thc t, cc i tng thng c tru tng ha qua vic nh ngha ca cc lp (class).
Tp hp cc gi tr hin c ca cc thuc tnh to nn trng thi ca mt i tng.Mi phng thc hay mi d liu ni ti cng vi cc tnh cht c nh ngha (bi ngi lp trnh) c xem l mt c tnh ring ca i tng. Nu khng c g lm ln th tp hp cc c tnh ny gi chung l c tnh ca i tng.
Lp trnh hng i tng l mt phng php lp trnh c cc tnh cht chnh sau:
Tnh tru tng (abstraction):y l kh nng ca chng trnh b qua hay khng ch n mt s kha cnh ca thng tin m n ang trc tip lm vic ln, ngha l n c kh nng tp trung vo nhng ct li cn thit. Mi i tng phc v nh l mt ng t c th hon tt cc cng vic mt cch ni b, bo co, thay i trng thi ca n v lin lc vi cc i tng khc m khng cn cho bit lm cch no i tng tin hnh c cc thao tc. Tnh cht ny thng c gi l s tru tng ca d liu.
Tnh tru tng cn th hin qua vic mt i tng ban u c th c mt s c im chung cho nhiu i tng khc nh l s m rng ca n nhng bn thn i tng ban u ny c th khng c cc bin php thi hnh. Tnh tru tng ny thng c xc nh trong khi nim gi l lp tru tng hay hay lp c s tru tng.
Tnh ng gi (encapsulation) v che du thng tin (information hiding): Tnh cht ny khng cho php ngi s dng cc i tng thay i trng thi ni ti ca mt i tng. Ch c cc phng thc ni ti ca i tng cho php thay i trng thi ca n. Vic cho php mi trng bn ngoi tc ng ln cc d liu ni ti ca mt i tng theo cch no l hon ton ty thuc vo ngi vit m. y l tnh cht m bo s ton vn ca i tng.
Tnh a hnh (polymorphism):Th hin thng qua vic gi cc thng ip (message). Vic gi cc thng ip ny c th so snh nh vic gi cc hm bn trong ca mt i tng. Cc phng thc dng tr li cho mt thng ip s ty theo i tng m thng ip c gi ti s c phn ng khc nhau. Ngi lp trnh c th nh ngha mt c tnh (chng hn thng qua tn ca cc phng thc) cho mt lot cc i tng gn nhau nhng khi thi hnh th dng cng mt tn gi m s thi hnh ca mi i tng s t ng xy ra tng ng theo c tnh ca tng i tng m khng b nhm ln.
Th d khi nh ngha hai i tng hinh_vuong v hinh_tron th c mt phng thc chung l chu_vi. Khi gi phng thc ny th nu i tng l hinh_vuong n s tnh theo cng thc khc vi khi i tng l hinh_tron.
Tnh k tha (inheritance):c tnh ny cho php mt i tng c th c sn cc c tnh m i tng khc c thng qua k tha. iu ny cho php cc i tng chia s hay m rng cc c tnh sn c m khng phi tin hnh nh ngha li. Tuy nhin, khng phi ngn ng nh hng i tng no cng c tnh cht ny.
3. Cc khi nim lin quan n cc ngn ng lp trnh OOP hin iLp (class)Mt lp c hiu l mt kiu d liu bao gm cc thuc tnh v cc phng thc c nh ngha t trc. y l s tru tng ha ca i tng. Mt i tng s c xc lp khi n c thc th ha t mt lp. Khc vi kiu d liu thng thng, mt lp l mt n v (tru tng) bao gm s kt hp gia cc phng thc v cc thuc tnh. c mt i tng (m c th c xem nh l mt bin) hot ng c th vic thc th ha s c th bao gm vic ci t cc gi tr ban u ca cc thuc tnh cng nh vic ng k b nh, m cng vic ny thng c giao cho cc phng thc gi l my kt cu (constructor) hay hm dng. Ngc li khi mt i tng thuc v mt lp khng cn s dng na th cng c th c mt phng thc x l gi l my hy dit (destructor) hay hm hy.
Nh vy, c c cc i tng th ngi lp trnh OOP cn phi thit k lp ca cc i tng bng cch xy dng cc thuc tnh v cc phng thc c cc c tnh ring.
Mi mt phng thc hay mt thuc tnh y ca mt lp cn c gi tn l mt thnh vin (member) ca lp .
Lp con (subclass)Lp con l mt lp thng thng nhng c thm tnh cht k tha mt phn hay ton b cc c tnh ca mt lp khc. Lp m chia s s k tha gi l lp ph mu (parent class).
Lp tru tng hay lp c s tru tng (abstract class)
Lp tru tng l mt lp m n khng th thc th ha thnh mt i tng thc dng c. Lp ny c thit k nhm to ra mt lp c cc c tnh tng qut nhng bn thn lp cha c ngha (hay khng ngha) c th tin hnh vit m cho vic thc th ha.
V d: Lp hinh_phang c nh ngha khng c d liu ni ti v ch c cc phng thc (hm ni ti) tinh_chu_vi, tinh_dien_tich. Nhng v lp hnh_phng ny cha xc nh c y cc c tnh ca n (c th cc bin ni ti l ta cc nh nu l a gic, l ng bn knh v to tm nu l hnh trn, ) nn n ch c th c vit thnh mt lp tru tng. Sau , ngi lp trnh c th to ra cc lp con chng hn nh l lp tam_giac, lp hinh_tron, lp tu_giac,. V trong cc lp con ny ngi vit m s cung cp cc d liu ni ti (nh l bin ni ti r lm bn knh v hng s ni ti Pi cho lp hinh_tron v sau vit m c th cho cc phng thc tinh_chu_vi v tinh_dien_tich).
Phng Thc (method)L hm ni ti ca mt lp (hay mt i tng). Ty theo c tnh m ngi lp trnh gn cho, mt phng php c th ch c gi bn trong cc hm khc ca lp , c th cho php cc cu lnh bn ngoi lp gi ti n, hay ch cho php cc lp c quan h c bit nh l quan h lp con, v quan h bn b (friend) c php gi ti n. Mi phng php u c th c kiu tr v, chng c th tr cc kiu d liu c in hay tr v mt kiu l mt lp c nh ngha t trc. Mt tn gi khc ca phng php ca mt lp l hm thnh vin.
Ngi ta cn nh ngha thm vi loi phng php c bit:
Hm dng (constructor) l hm c dng ci t cc gi tri ban u cho cc bin ni ti v i khi cn dng khai bo v vic x dng b nh.Hm hy (destructor) l hm dng vo vic lm sch b nh v hy b tn ca mt i tng sau khi dng xong, trong c th bao gm c vic xa cc con tr ni ti v tr v cc phn b nh m i tng dng.Trong mt s trng hp th hm hy hay hm dng c th c t ng ha bi ngn ng OOP nh l trng hp ca Visual C++, C#.
Tin ch (utility) l cc hm ch hat ng bn trong ca mt lp m khng cho php mi trng bn ngoi gi ti. Cc hm ny c th l nhng tnh ton trung gian ni b ca mt i tng m xt thy khng cn thit phi cho th gii bn ngoi ca i tng bit l g.
Thuc tnh (attribute)Thuc tnh ca mt lp bao gm cc bin, cc hng, hay tham s ni ti ca lp . y, vai tr quan trng nht ca cc thuc tnh l cc bin v chng s c th b thay i trong sut qu trnh hot ng ca mt i tng. Cc thuc tnh c th c xc nh kiu v kiu ca chng c th l cc kiu d liu c in hay l mt lp nh ngha t trc. Nh ghi, khi mt lp c thc th ho thnh i tng c th th tp hp cc gi tr ca cc bin ni ti lm thnh trng thi ca i tng. Ging nh trng hp ca phng php, ty theo ngi vit m, bin ni ti c th ch c dng bn trong cc phng php ca chnh lp , c th cho php cc cu lnh bn ngoi lp, hay ch cho php cc lp c quan h c bit nh l quan h lp con, (v quan h bn b (friend) trong C++) c php dng ti n (hay thay i gi tr ca n). Mi thuc tnh ca mt lp cn c gi l thnh vin d liu ca lp .
Thc th (instance)Thc th ha (instantiate) l qu trnh khai bo c mt tn (c th c xem nh l mt bin) tr thnh mt i tng t mt lp no .
Mt lp sau khi c tin hnh thc th ha c mt i tng c th gi l mt thc th. Hay ni ngc li mt thc th l mt i tng ring l ca mt lp nh trc. Nh cc bin thng thng, hai thc th ca cng mt lp c th c trng thi ni ti khc nhau (xc nh bi cc gi tr hin c ca cc bin ni ti) v do hon ton c lp nhau nu khng c yu cu g c bit t ngi lp trnh.
Cng cng (public)Cng cng l mt tnh cht c dng gn cho cc phng php, cc bin ni ti, hay cc lp m khi khai bo th ngi lp trnh cho php cc cu lnh bn ngoi cng nh cc i tng khc c php dng n n.
Th d: Trong C++ khai bo public: int my_var; th bin my_var c hai tnh cht l tnh cng cng v l mt integer c hai tnh cht ny hp thnh c tnh ca bin my_var khin n c th c x dng hay thay i gi tr ca n (bi cc cu lnh) mi ni bn ngoi ln bn trong ca lp.
Ring t (private)Ring t l s th hin tnh cht ng mnh nht (ca mt c tnh hay mt lp)Khi dng tnh cht ny gn cho mt bin, mt phng php th bin hay phng php ch c th c s dng bn trong ca lp m chng c nh ngha. Mi n lc dng n chng t bn ngoi qua cc cu lnh hay t cc lp con s b ph nhn hay b li.
Bo tn (protected)Ty theo ngn ng, s c vi im nh khc nhau v cch hiu tnh cht ny. Nhn chung y l tnh cht m m khi dng p dng cho cc phng php, cc bin ni ti, hay cc lp th ch c trong ni b ca lp hay cc lp con ca n (hay trong ni b mt gi nh trong Java) c php gi n hay dng n cc phng php, bin hay lp .
So vi tnh cht ring t th tnh bo tn rng ri hn v ngha chia s d liu hay chc nng. N cho php mt s trng hp c dng ti cc c tnh ca mt lp (t mt lp con chng hn).
Lu : Cc tnh cht cng cng, ring t v bo tn i khi cn c dng ch th cho mt lp con cch thc k tha mt lp cha m nh trong C++.
a k tha (muliple inheritance)y l mt tnh cht cho php mt lp con c kh nng k tha trc tip cng lc nhiu lp khc.
Vi im cn lu khi vit m dng tnh cht a k tha:
Khi mun c mt s k tha t nhiu lp ph mu th cc lp ny cn phi c lp v c bit tn ca cc d liu hay hm cho php k tha phi c tn khc nhau trnh li ambiguilty. Bi v lc phn mm chuyn dch s khng th xc nh c l lp con s tha k tn no ca cc lp ph mu.Khng phi ngn ng OOP loi phn lp no cng h tr cho tnh cht ny.Ngoi cc khi nim trn, ty theo ngn ng, c th s c cc chc nng OOP ring bit c cp thm vo.
Kt lun:Bi ny mnh ch tp trung vo phn gii thiu l thuyt. Bi tip theo mnh s gii thiu n cc bn cc c php c bn ca lp trnh hng i tng trong php.
Hc PHP: Lp trnh hng i tng vi PHP
biMinh Nht|Lp trnh WEB,PHP,PHP nng cao|19/08/2013Lp trnh hng i tng vi PHP gip cho vic lp trnh tr nn d dng hn. Lp trnh by gi khng ging nh vi ngy trc, tt c u hng v to dng mt i tng. Xy dng i tng trong PHP lm cho code tr nn r rng, trong sng v d sa i sau ny hn.
Trong PHP, ngi ta cung cp cho chng ta sn cc hm nh ngha i tng, v xy dng i tng kh l y . tit kim ch vit v thi gian c ca cc bn, ti xin gi tt i tng y l class.
Hnh dung mt class
Nu l ngi mi lp trnh hoc ngi quen vi cch xy dng hm v gi hm c in. Th s thy vic s dng class trong lp trnh tr nn nhc nhng v kh tip cn. Mnh hiu vn , v khi ln u mnh nghe n nh ngha class cng thy hi kh chu. Tuy nhin mnh s lm bn cm thy d chu hn khi lp trnh hng i tng bng ngn ng PHP qua bi vit ny.
im khc bit gia lp trnh hng i tng v lp trnh hng th tc (hm)
i vi lp trnh theo hng th tc, tc cch m ta vn thng lm. Xy dng mt hm, ri include n t mt file khc, gi hm, .
1ham_cua_tui();
Cn s dng i tng th sao. gi mt hm m s dng i tng th t nht bn phi tn 2 dng code.
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3$obj = new myClass();
$obj -> ham_cua_tui();
Mt to mi i tng. V mt gi hm. Mnh s ni cho bn nghe v sao m i tng tuy di nhng li c a chung n th.
Th nht, l s dng i tng lm cho ta cm thy gn gi hn. V t trc gi, con ngi quen vi vic tng tc ln mt i tng. Mi th xung quanh ta u l i tng: chic laptop, ci in thoi, hay ci TV, tt c u l i tng. Cng v vy m ngi ta cng lm code tr thnh mt i tng.
Bn s cm thy c s quan h tng tc qua li gia cc i tng khi lp trnh. Chn hng nh:
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4Mnh t = new class Mnh t;Ngi nh = new class Nh;
Mnh t -> thm ( Ngi nh );
Bn s cn mt thi gian thy c s ri nhau ca tng i tng trong code, v tng tng ra c s tng tc ca chng vi nhau. V cng ng lo ngi, v ngy s n sm.
iu cui cng lm cho class tr thnh mt cng c tuyt vi khi lp trnh. l s dng li ca class con vi class cha. Lm cho code d dng ci tin nhanh chng da trn nhng ci c.
3 iu cn quan tm khi xy dng mt class
Mt class c 3 th quan trng.
K tha class ang xy dng c cn phi k tha class no khc c th hot ng hay khng
Thuc tnh cc thuc tnh m class ny cn c, hiu nm n n l mt bin ton cc dng chung trong cc hm ca class ny v bn ngoi trong mt s trng hp
Hm v phn quan trng nht. Bn c th hiu n gin, y l cc chc nng m class cung cp. Trong c mt hm c bit, gi l hm xy dng construct. Hm ny s c gi ngay lc bn new mt class. Thng c dng khi to gi tr cho bin.
K thaNu bn mi nghe n ln u th, Ok mnh s gii thch cho bn. K tha m ch vic mt class con, s dng li cc thuc tnh, v hm ca class cha hot ng. V mt lu tr, th trong class con s cha lun class cha. ng hiu ngc li l cha cha con nh.
Xy dng class bng PHP
Tin hnh to mt class n gin, qua v d bn di ta s to mt class mi tn l myClass:
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34// Khai bo tn class
class myClass {
// Ni dung bn trong class// Cc thuc tnh ca class
private $pri;public $pub;protected $pro;
// Hm ca class
function __construct() {
// Hm construct
$this->pri = "Bin private";$this->pub = "Bin public";$this->pro = "Bin protected";}
function xuat() {
// Hm xut tr
echo '$pri: ' . $this->pri;echo '$pub: ' . $this->pub;echo '$pro: ' . $this->pro;}
}
// Kt thc mt khai bo hm
Bin $this
Bin $this dng m ch i tng hin ti, class m bn ang vit code. Vic dng $this gi, hoc c v ghi gi tr vo bin thuc phm vi chung ca class l bt buc. V d:
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17class A {private $bien1;function hamA() {echo "Hm hamA() ca class A c gi";}function hamB() {// hamB() mun gi hm hamA ca class$this -> hamA();// hamB() mun t gi tr cho bin $bien1$this -> bien1 = "Hello";}}// Ht class A
function hamA() {echo "Hm hamA() bn ngoi class";}
Nu bn c gi hamA() m khng dng $this -> hamA(). Th PHP s gi hamA() bn ngoi class, ch khng gi hamA() trong class. Hoc PHP s bo li.
i vi bin, nu bn c gn bng lnh $bien1 = Hello; Th bin cc b $bien1 s c to bn trong hamB(), v lu gi tr l Hello ch khng lu vo bin $bien1 dng 2. Ni chung, ta phi dng $this -> gi hm hoc nhng bin thuc v class.
Lu Xin nh k l khi thao tc vi bin:$this -> tenbien. Khng phi l$this -> $tenbien.
Phn bit private, public, protected khi lp trnh hng i tng vi PHPim chung duy nht ca 3 t kha ny u l t kha ch tm vc ca bin. Hay con gi l ng cnh, phm vi m bin ny c th c truy cp t.
Khc nhau:
Private: Kht khe nht, ch trong class khai bo bin ny mi c quyn s dng.
Public: C th truy cp t mi ni thng qua cu lnh$obj -> tn_bin; Protected: t kht khe hn Private mt cht, ngoi class khng th truy cp c bin ny. Tuy nhin class con th c th.
V d minh ha:
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9// S dng li class code trn
$class = new myClass();
echo $class->pub; // Bin publicecho $class->pri; // Li fatalecho $class->pro; // Li fatal
$class -> xuat(); // Bin public, Bin private, Bin protected
Nh ni trn, bin private v protected ch dng c bn trong class. l l do hmxuat()c th dng c 2 bin ny xut ra kt qu.
V khng ch p dng vi bin, 3 t kha ny cn c p dng cho hm vi ngha tng t. Khc vi bin mt t, l khi khng t kha ny vo th mc nh hm s l public. Tc c th gi hm t bn ngoi class.
Class k thaCch k tha kh ging C++. Nh gii thiu trn, class con k tha class cha s tha hng tt c cc thuc tnh, hm ca class cha. Chng ta cng xem li s mt class.
Trong php, dng t kha extends khi khai bo class biu th l class ny ang s dng li mt class khc lm cha ca n.
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3class myNewClass extends myClass {// code}
Nh on code trn l myNewClass k tha myClass.
Trong class con c th gi li cc hm khng phi l private ca class cha nh l mt hm ca chnh n. (myClass l class u bi)
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8class myNewClass extends myClass {
function xuat2() {echo "Hm c gi t class con";$this->xuat();}
}
Vy class con ny s c nhng c tnh quan trng?
Class con c th trc tip truy cp bin v gi hm ca class cha c khai bo vi t kha public hoc protected.V lu tr, class con l mt class ln hn class cha. V cha lun c class cha (xem hnh trn).
Vit hm ln hm c ca class chaKhi vit code cho class con, nu bn cm thy mt hm ca class cha khng ph hp, v bn mun vit li hm ny, vit ln hm c ca class cha.
Vic vit hm ny cn gi l override
Vic vit rt n gin, ta ch cn khai bo mt hm vi tn y chang tn hm ca class cha, PHP s t hiu bn ang mun lm g. V d v vit hm:
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17class CoBan {function print() {echo "Hm print() ca class CoBan";}}
class KeThua extends CoBan {function print() {echo "Hm print() ca class KeThua";}}
$obj1 = new CoBan();$obj2 = new KeThua();
$obj1 -> print(); // Xut: Hm print() ca class CoBan$obj2 -> print(); // Xut: Hm print() ca class KeThua
Gi li hm b vit trn ta va tm hiu v vit hay override hm ca class cha trong PHP. Vy trng hp hm b ghi mt ri th ta s khng gi c na. Lm sao gi li hm ca class cha y? PHP gii quyt vn ny bng t khaparent::.
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19class A {function print() {echo "A";}}
//Class B k tha class Aclass B extends A {function print() {parent::print(); // gi hm print() ca class Aecho "B";}}
$obj = new A();$obj -> print(); // Kt qu: A
$obj = new B();$obj -> print(); // Kt qu: AB
Ngun bi vit:http://minhnhut.info/lap-trinh-huong-doi-tuong-voi-php/#ixzz2y1Mcurrq
