chapter8 exception handling

7/23/2019 Chapter8 Exception Handling

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xception Handling in

Java

Types of rrors

1.Compile time

All syntax errors identified by java

compiler.

No class file is created wen tis occ!rs.

"o it is necessary to fix all compile time

errors for s!ccessf!l compilation.

gs#

$issing of semicolon%

!se of & instead of &&

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Java

'.(!n time

"ome pgms may not r!n s!ccessf!lly d!e

to wrong logic or errors li)e stac)

overflow.

"ome of te Common r!n time errors are#

*ivision by +

Array index o!t of bo!nds

Negative array si,e etc..

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Java

xception is a condition ca!sed by a r!n time

error in te program. -en te java interpreter

identifies an error s!c as division by + it

creates an xception object and trows it

*efinition#

An

e eption

is an event% wic occ!rs d!ring

te exec!tion of a program% tat disr!pts te

normal flow of te program/s instr!ctions.

0s defined as a condition tat interr!pts te

normal flow of operation witin a program.

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Exception Handling in Java

Java allows xception andling mecanism to

andle vario!s exceptional conditions. -en an

exceptional condition occ!rs% an e eptionis

said to be trown.

or contin!ing te program exec!tion% te !ser

so!ld try to catc te exception object trown

by te error condition and ten display an

appropriate message for ta)ing corrective

actions. Tis tas) is )nown as xception

andling

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Java

Tis mecanism consists of #

1. ind te problem2Hit te xception3

'. 0nform tat an error as occ!rred2Trow

te xception3

4. (eceive te error 0nformation2Catc te

xception3

5. Ta)e corrective actions2Handle te

xception3

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Java

0n Java xception andling is managed by 6

)ey words#

try

catc

trow

trows

finally

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xception Handling in Java

8

Trowable

Exception error

0nterr!ptedException

2cec)ed exception3

(!ntimeException

2!ncec)ed exception3

xception

Hierarcy

7ac)age java.lang


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8ncec)ed exception#Tese exception need not be incl!ded in an

metod9s trowslistTe compiler does not cec) to see if a metod

andles or trows tese exception

tese are s!bclasses of (!ntime xceptionTe compiler doesn/t force client programmerseiter to catc te exception or declare it in atrows cla!se.

Class Error and its s!bclasses also are !ncec)ed.Cec)ed exception#

$!st be incl!ded in an metod9s trowslist if tatmetod can generate one of tose exceptions and doesnot andle it itself

Tese exception defined by java.lang

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10

Exception Meaning

ArithmeticException Arithmetic error, such as divide-by-zero

ArrayIndexOutOfBoundsException Array index is out-of-bounds

ArrayStoreException Assignment to an array element of anincompatible type

lassastException Invalid cast

Enumonstant!ot"resentException An attempt is made to use an unde#nedenumeration value

IllegalArgumentException Illegal argument used to invo$e a method

Illegal%onitorStateException Illegal monitor operation, such as &aiting onan unloc$ed thread

IllegalStateException Environment or application is in incorrectstate

Illegal'hreadStateException (e)uested operation not compatible &ithcurrent thread state

IndexOutOfBoundsException Some type of index is out-of-bounds

!egativeArraySizeException Array created &ith a negative size

Javas unchecked RuntimeException subclasses defined injava.lang


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Exception Meaning

!ull"ointerException Invalid use of a null reference

!umber*ormatException Invalid conversion of a string to a numericformat

SecurityException Attempt to violate security

StringIndexOutOfBoundsException Attempt to index outside the bounds of a

string

'ype!ot"resentException 'ype not fount

+nsupportedOperationException An unsupported operation &as encountered


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Javas checked Exceptindefined injava.lang

Exception Meaning

lass!ot*oundException lass not found

lone!otSupportedException Attempt to clone an obect that does notimplement the Cloneable interface

IllegalAccessException Access to a class is denied

InstantiationException Attempt to create an obect of an abstractclass or interface

InterruptedException One thread has been interrupted by anotherthread

!oSuch*ieldException A re)uested #eld does not exist!oSuch%ethodException A re)uested method does not exist


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class x:

p!blic static void main2"tring args;


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Java

try @ catc

try Block

Statement that

causes Exception

Catch Block

Statement that

causes Exception

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Java

try:"tatement#

?

catc2Exceptiontype e3:

statement=

?

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Javaclass Ex:

p!blic static void main2"tring args;d=

"ystem.o!t.println2Bfrom tryB3=

?catc2AritmeticException e3

:

"ystem.o!t.println2Bdivsn by eroB3=

?

"ystem.o!t.println2Bafter catcB3=

?

?

Dnce an exception is

trown % program control

transfers o!t of te try

bloc) into te catc bloc).

Dnce te catc statement

is exec!ted pgm control

contin!es wit te next

line following te entire

try>catc mecanism.

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Java

-e can display te description of an Exception in

a println statement by simply passing teexception as an arg!ment.

catc2AritmeticException ae3:

"ystem.o!t.println2Exception#FGae3=

?

o>p

Exception#java.lang.AritmeticException# >by

,ero

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Common Trowable

metods

get$essage23= All trowable objects can ave an

associated error message. Calling tis message will

ret!rn te message if one present.

getocali,ed$essage23= gets te locali,ed version of

error message.

print"tac)Trace23= sends te stac) trace to te system

console. Tis is a list of metod calls tat led to te

exception condition. 0t incl!des line n!mber and file

names too. 7rinting of te stac) trace is te defa!lt

beavior of a r!ntime exception wen ! don9t catc it

o!rselves.

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catc2Aritmetic xception e3:

"ystem.o!t.println2e.get$essage233=

>>e.print"tac)Trace23=

?

o>p# #IJAA7K$"Ljava x

> by ,ero

catc2Aritmetic xception e3:

e.print"tac)Trace23=

?

#IJAA7K$"Ljava x

o>p#

java.lang.Aritmetic xception# > by ,ero

at x.main2 x.java#M3

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8se of get$essage23 andprint"tac)Trace23



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$!ltiple catc "tatement

some cases% more tan one exception co!ld be raised by

a single piece of code.

s!c cases we can specify two or more catc cla!ses%

eac catcing a different type of exception.

wen an exception trown% eac catc statement is

inspected in order% and te first one wose type matces

tat of te exception is exec!ted.

After 1 catc statement is exec!ted% te oters arebypassed and exec!tion contin!es after te try>catc

bloc).

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Java

class Ex:p!blic static void main2"tring

args;len=int c;


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Java

0n m!ltiple catc statement exception s!bclassesm!st come before any of teir s!perclasses.

eca!se a catc statement tat !ses a

s!perclass will catc exception of tat type pl!s

any of its s!bclasses.T!s a s!bclass wo!ld never be reaced if it

came after its s!perclass.

!rter java compiler prod!ces an error!nreacable code.

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JavaNested try statementtry statement can be nested

class x:

p!blic static void main2"tring dd;len=

"ystem.o!t.println2a3=

try:

if2len&&13

len&len>2lenlen3=

if2len&&'3:

int c;


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E#IJAA7K$"Ljava Ex

java.lang.AritmeticException# > by ,ero

at Ex.main2Ex.java#M3

after catc

E#IJAA7K$"Ljava Ex '+

1+

java.lang.AritmeticException# > by ,ero at Ex.main2Ex.java#153

after catc

E#IJAA7K$"Ljava Ex '+ 4+

6

Array indexjava.lang.Array0ndexD!tDfo!ndsException# 1+

after catc

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Java

trow

0t is possible to trow an exception explicitly.

"yntax#

trowTrowable0nstance

trowable0nstancem!st b an object of type Trowable or a

s!bclass of Trowable.

y two ways we can obtain a Trowable object

1. 8sing parameter into a catc cla!se

'. Creating one wit new operator

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Java

class trow*emo:



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#IJAA7K$"Ljava trow*emo 5

java.lang.NegativeArray"i,e xception#

0llegal Array si,e

xception in tread BmainB

java.lang.NegativeArray"i,e xception#

0llegal Array si,e

at

trow*emo.main2trow*emo.java#1P3

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Java


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Java

trows

0f a metod ca!sing an exception tat it doesn/t

andle% it m!st specify tis beavior tat callers

of te metod can protect temselves against

te exception.

Tis can be done by !sing trows cla!se.

trows cla!se lists te types of exception tat a

metod migt trow.

orm

type metodname2parameter list3 trows

Exception list

:>>body of metod? 28


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Java

import java.io.Q=

class Trows*emo:



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Java

finally

0t creates a bloc) of code tat will be exec!ted after try>catc

bloc) as completed and before te code following try>catc

bloc).

0t will exec!te weter or not an exception is trown

finally is !sef!l for#

RClosing a file

RClosing a res!lt set

RClosing te connection establised wit database

Tis bloc) is optional b!t wen incl!ded is placed after te last

catc bloc) of a try

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Java

orm#

try

:?

catc2exceptiontype

e3

:?

finally

:?

finally

finally

Catch block

try block

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JavaCreating o!r own Exception class

or creating an exception class o!r own simply

ma)e o!r class as s!bclass of te s!per class

Exception.

Eg#

class $y xceptionextends xception:

$y xception2"tring msg3:

s!per2msg3=

?

?

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class Test$yException:

p!blic static void main2"tring args;2float3y=

if2,O+.+13:

trow new $yException2Btoo small n!mberB3=?

?catc2$yException me3:

"ystem.o!t.println2Bca!gt my exceptionB3=

"ystem.o!t.println2me.get$essage233=

?

finally:

"ystem.o!t.println2Bfrom finallyB3=

?

?

?

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#IJAA7K$"Ljava

Test$y xception

ca!gt my exception

too small n!mber

from finally

D>7#


chapter8 exception handling

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