Bai7 Exception

8/3/2019 Bai7 Exception

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GING VIN:V TN DNG

TRNG CAO NG CNG NGH THNG TIN TP.HCM

NHP MN JAVA

BI 7X L NGOI L(EXCEPTION)

GV:VT

nDng


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X l li v ngoi l Khi try/catch/finally

Cc lp ngoi l

Xy dng lp ngoi l

Lan truyn ngoi l

Tung li ngoi l Bi tp

NI DUNG TRNH BY


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Trong mt s ngn ng nh C, vic x l lithng c ci t ngay ti cc bc thc hinca chng trnh. Cc hm s tr v mt cutrc li khi gp li.

V d: Tm kim phn t trong mt danh schErrorStruct error = new ErrorStruct();

TableEntry entry = lookup(Marianna, employee, error);

if (entry == null){

return error;

}

X L LI V NGOI L


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M lnh v m x l li nm xen k khin lptrnh vin kh theo di c thut ton chnhca chng trnh.

Khi mt li xy ra ti hm A, tt c cc li gihm lng nhau n A u phi x l li m Atr v.

X L LI V NGOI L


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Trong Java, vic x l li c th c ci ttrong mt nhnh c lp vi nhnh chnh cachng trnh.

Li c coi nh nhng trng hp ngoi l(exceptional conditions). Chng c bt/nm(catch and throw) khi c li xy ra.

=> Mt trng hp li s ch c x l ti ni

cn x l.=> M chnh ca chng trnh sng sa, ngvi thit k thut ton.

X L LI V NGOI L


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import java.awt.Point;

public class MyArray{

public static void main(String[ ] args) {System.out.println("Goi phuong thuc methodeX()");methodeX();System.out.println("Chuong trinh ket thuc binh thuong");

}

public static void methodeX() {Point[ ] pts = newPoint[10];for(int i = 0; i < pts.length; i++) {

pts[i].x = i;pts[i].y = i+1;}

}}

V D 1


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Goi phuong thuc methodeX()Exception in thread "main" java.lang.NullPointerException

at MyArray.methodeX(MyArray.java:14)at MyArray.main(MyArray.java:7)

Gii thch: H thng tung ra mt exception thuc lpNullPointerExceptionkhi gp li. Sau chng trnh ktthc.

KT QU THC THI V D 1


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public class MyDivision {

public static void main(String[ ] args) {System.out.println("Goi phuong thuc A()");A();System.out.println("Chuong trinh ket thuc binh thuong");

}

public static void A() {B();

}public static void B() {

C();

}public static void C() {float a = 2/0;

}}

V D 2


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Goi phuong thuc A()Exception in thread "main" java.lang.ArithmeticException: / by zero

at MyDivision.C(MyDivision.java:14)at MyDivision.B(MyDivision.java:11)at MyDivision.A(MyDivision.java:8)

at MyDivision.main(MyDivision.java:4)

Gii thch: Phng thc A() gi B(), B() gi C(), C() gy ra lichia cho 0 v h thng nm ra mt exception thuc lp

ArithmeticException. Sau chng trnh kt thc.

KT QU THC THI V D 2


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Khi mt phng thc gp li no , v dnh chia khng, vt kch thc mng,m file cha tn ti th cc ngoi l sc nm ra. Chng trnh dng li ngaylp tc, ton b phn m pha sau skhng c thc thi.

Java h tr cch thc x l ngoi l

(exception handling) tu theo nhu cu cachng trnh.

NGOI L


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Khi try/catch t on m c kh nng xy ra ngoi l

trong khi try

t on m x l ngoi l trong khi catch Khi xy ra ngoi l trong khi try, cc culnh trong khi catch s c thc hin tuvo kiu ca ngoi l.

Sau khi thc hin xong khi catch, iukhin s c tr li cho chng trnh.

X L NGOI L


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V d 1:try{

methodeX();System.out.println(Cau lenh ngay sau methodX());

}catch (NullPointerException e){

System.out.println(Co loi trong khoi try);}System.out.println(Cau lenh sau try/catch);

KHI TRY/CATCH


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try {

x = System.in.read();System.out.println(x = + x);} catch (IOException e) {

System.out.println(Error: + e.getMessage());}

try {A();

} catch (Exception e) {System.out.println(Co loi trong A());

}

V d 2:

V d 3:

KHI TRY/CATCH


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try{

String s = buff.readLine();int a = Integer.parseInt(s);x[i++] = a;

} catch (IOException e) {System.out.println(Error IO: + e.getMessage());

} catch (NumberFormatException e) {System.out.println(Error Format: + e.getMessage());

} catch (ArrayIndexOutOfBoundsException e) {System.out.println(Error Index: + e.getMessage());}

V d 4:

KHI TRY/CATCH


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Khi mt ngoi l xy ra, chng trnh dng li,mt s cng vic dn dp c th s khngc thc hin (v d nh ng file).

Khi finally m bo rng cc cu lnh trong

lun c thc hin, k c khi ngoi l xyra.try{

doSomething(); // phng thc ny c th gy ra ngoi l} finally {

cleanup();}

KHI FINALLY


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Cc ngoi l xy ra khi gp li. C th bt v x l cc ngoi l bng cch s

dng khi try/catch. Nu khng chng trnhs kt thc ngay (vi ng dng console) hoc

tip tc tn ti (vi ng dng GUI). Khi bt ngoi l, phi bit r kiu ngoi l cn

bt. C th dng kiu cha Exception.

chc chn vic dn dp lun c thchin, dng khi finally. C th kt hptry/catch/finally.

TM TT V X L NGOI L


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ClassNotFoundException

Throwable

Error Exception

RuntimeExceptionAssertionError IOException

Object

NullPointerException ArithmeticException

MT S LP NGOI L


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Lp Throwable C mt bin String lu thng tin chi tit v

ngoi l xy ra

Mt s phng thc c bn Throwable(String s); // To mt ngoi l c tn ls.

String getMessage(); // Ly thng tin v ngoi l

void printStackTrace(); // In ra tt c cc thng tinlin quan n ngoi l

MT S LP NGOI L


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Lp Exception C nhiu ngoi l thuc lp con ca

Exception.

Ngi dng c th to ra cc ngoi l k

tha t Exception. Lp Error

Ch nhng li nghim trng v khng d

on trc c nh ThreadDead,LinkageError, VirtualMachineError...

Cc ngoi l kiu Error t c x l.

MT S LP NGOI L


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RuntimeException: Ch cc ngoi l c th

xy ra khi JVM thc thi chng trnh NullPointException: con tr null

OutOfMemoryException: ht b nh

ArithmeticException: li ton hc, li chiakhng

ClassCastException: li p kiu

ArrayIndexOutOfBoundsException: vt quch s mng

...

MT S LP NGOI L


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Ngoi l unchecked L cc ngoi l khng bt buc phi ckim tra.

Gm RuntimeException, Error v cc lp conca chng.

Ngoi l checked L cc ngoi l bt buc phi c kim tra.

Gm cc ngoi l cn li.

HAI LOI NGOI L


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Gi s method1 gi method2 v method2l phng thc c kh nng nm ngoi lkiu checked, lc : hoc method2 phi nm trong khi try/catch.

hoc phi khai bo method1 c kh nngnm (throws) ngoi l.

CH VI NGOI L CHECKED


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Cch 1: try/catchpublic static void main(String[] args){

try {String s = buff.readLine();

} catch (IOException e) {...

}

}

Cch 2: Khai bo throwspublic static void main(String[ ] args) throwsIOException{

String s = buff.readLine();

}

V D (NGOI L IOException)


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Bi 1: Ci t x l cc ngoi l chochng trnh tnh thng 2 s bng giaodin GUI.

Bi 2: Ci t x l li bng cch dngngoi l cho v d phn u bi.

Bi tp


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nh ngha lp ngoi l// file MyException.java

public class MyException extendsException{

public MyException(String msg){

super(msg);}

}

NGOI L DO NGI DNG TO


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S dng ngoi l// file ExampleException.javapublic class ExampleException{

public void copy(String fileName1, String fileName2)throws MyException

{if(fileName1.equals(fileName2))

throw newMyException("File trung ten"); // tung ngoi l

System.out.println("Copy completed");}

Khai bo kh nng tung ngoi l

Tung ngoi l



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S dng ngoi lpublic static void main(String[] args){

ExampleException obj = new ExampleException();try {

String a = args[0];String b = args[1];obj.copy(a,b);

} catch (MyException e) {System.out.println(e.getMessage());

}}

}



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Tnh hung Gi s trong main() gi phng thc A(),

trong A() gi B(), trong B() gi C(). Khi mt

ngn xp cc phng thc c to ra. Gi s trong C() xy ra ngoi l.

LAN TRUYN NGOI L


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C()B()

A()

main()

B()

A()

main()

C() tung ngoi l

Nu C() gp li v tung ra ngoi l nhng trong C() li khng x lngoi l ny, thch cn mt ni c th x l chnh l ni m C() cgi, l trong phng thc B(). Nu trong B() cng khng x l th

phi x l ngoi l ny trong A()Qu trnh ny gi l lan truynngoi l.

Nu n main() cng khng x l ngoi l c tung t C() thchng trnh s phi dng li.

LAN TRUYN NGOI L


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Trong khi catch, ta c th khng x l trc

tip ngoi l m li nm li ngoi l choni khc x l.

catch (IOException e) {throw e;

}

Ch : Trong trng hp trn, phng thccha catch phi bt ngoi l hoc khai bo

throws cho ngoi l (nu l loi checked).

NM LI NGOI L


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Khng nn s dng ngoi l thay cho cclung iu khin trong chng trnh. V d: Kim tra delta trong chng trnh gii

phng trnh bc 2.

Nn thit k v s dng ngoi l mt cchthng nht cho ton b d n.

Mt s x l li bng ngoi l ph bin l: ht

b nh, vt qu ch s mng, con tr null,chia cho 0, i s khng hp l...

CH KHI S DNG NGOI L


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1. Vit chng trnh cho php tnh gi tr ca biuthc:

A =

Yu cu x l cc ngoi l c th xy ra.

2. Vit chng trnh cho php to mt mng 2

chiu c mxn vi m,n nhp t bn phm. Cit cc x l ngoi l cn thit.

5x - y

2x + 7y

BI TP

BI TP


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3. Xy dng lp ngoi l DateException cho ccli v ngy thng.

4. Vit chng trnh cho php ngi dng nhpvo ngy, thng nm, nu thng tin ny khnghp l s tung ra mt ngoi l DateException,sau thng bo cho ngi nhp bit v chophp ngi dng nhp li.

BI TP

BI TP 5


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5. Tm hiu li lp Candidate hc (d liugm m th sinh, tn v im thi 3 mn). iug s xy ra khi to mt i tng thuc lpCandidate vi d liu a vo khng hp l ?

Ci t lp CandidateException bt cc linh trn. Yu cu khi c li th s cho bit ctn v m th sinh b li.

BI TP 5


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BI 7

V

TnDng

Bai7 Exception

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