Presentation on Exceptions in Java.ppt

8/16/2019 Presentation on Exceptions in Java.ppt

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Exception Handling in Java


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What is an exception?

An exception is an abnormal condition that changes the normal flowof control in a program An exception is an event, which occurs during the execution of aprogram, that disrupts the normal flow of the program's instructions


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T pes of Exception?

Types of Exception 1) Checked Exception !hec"ed exceptions are chec"ed at compile#time$ The classes that

extend Throwable class except %untimeException and Error are "nown

as chec"ed exceptions e$g$& Exception, ()*Exception etc$2) Unchecked Exception

The classes that extend %untimeException are "nown as unchec"edexceptions e$g$ ArithmeticException, +ull ointerException, Arra &ndex ut f-oundsException etc$ .nchec"ed exceptions are not

chec"ed at compile#time$3) Error

Errors are not possible to handle in our program code


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Exception Hierarch


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Exception Handling 0e words

There are 1 "e words used in 2ava exception handling$tr catch

finall throw throws


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tr -loc"

Java tr bloc" is used to enclose the code that might throw an exception$ &tmust be used within the method$Java tr bloc" must be followed b either catch or finall bloc"$

( ntax of 2ava tr #catch

tr 344code that ma throw exception5catch6Exception7class7+ame ref835( ntax of tr #finall bloc"

tr 3

44code that ma throw exception5finall 35


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catch -loc"

Java catch bloc" is used to handle the Exception$ &tmust be used after the tr bloc" onl $ 9ou can use multiple catch bloc" with a single tr $


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finall -loc"

Java finall bloc" is a bloc" that is used to executeimportant code such as closing connection, streametc$

Java finall bloc" is alwa s executed whetherexception is handled or not$Java finall bloc" must be followed b tr or catch bloc"$


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Example of tr #catch#finall

public class Test 3public static void main6(tring args:;83tr 3int data

( stem$out$println6data85catch6ArithmeticException e8

3( stem$out$println6e8 5finall

3( stem$out$println6@finall bloc" is alwa s executed@8 5( stem$out$println6@rest of the code$$$@85

5


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throw "e word

The Java throw "e word is used to explicitl throwan exception$ We can throw either chec"ed or unche"ed exception

in 2ava b throw "e word$ The throw "e word ismainl used to throw custom exception$( ntax of 2ava throw "e word is given below$

throw exception


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Example of throw "e word

public class TestThrow 3static void validate6int age83if6ageB C8throw new ArithmeticException6@not valid@8

else( stem$out$println6@welcome to vote@8

5public static void main6(tring args:;83

validate6 D8( stem$out$println6@rest of the code$$$@85

5


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throws "e word

The Java throws "e word is used to declare an exception$ &t gives aninformation to the programmer that there ma occur an exception so it is betterfor the programmer to provide the exception handling code so that normal flowcan be maintained$Exception Handling is mainl used to handle the chec"ed exceptions$ &f there

occurs an unchec"ed exception such as +ull ointerException, it isprogrammers fault that he is not performing chec" up before the code beingused$

( ntax of 2ava throws return7t pe method7name68 throws exception7class7name3

44method code5


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Exception propagation using throws "e word

import 2ava$io$& Exceptionclass Testthrows 3 void m68throws & Exception3

throw new & Exception6@device error@8 44chec"ed exception5

void n68throws & Exception3m68

5 void p683

tr 3n685catch6Exception e83( stem$out$println6@exception handled@8 55public static void main6(tring args:;83Testthrows ob2


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throws "e word6contd$8

Case1: You handle the exception&n case ou handle the exception, the code will be executed fine whether exception occurs during theprogram or not$import 2ava$io$class F3 void method68throws & Exception3

throw new & Exception6@device error@855public class Testthrows=3

public static void main6(tring args:;83tr 3F m


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You declare the exception A8&n case ou declare the exception, if exception does not occur, the code will be executed fine$-8&n case ou declare the exception if exception occures, an exception will be thrown at runtime because

throws does not handle the exception$Progra if exception does not occur import 2ava$io$

class F3 void method68throws & Exception3( stem$out$println6@device operation performed@8

55class TestthrowsD3

public static void main6(tring args:;8throws & Exception344declare exceptionF m


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Progra if exception occurs import 2ava$io$class F3 void method68throws & Exception3throw new & Exception6@device error@8

55class TestthrowsG3

public static void main6(tring args:;8throws & Exception344declare exceptionF m


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thro! thro!s

Java throw "e word is used toexplicitl throw an exception$

!hec"ed exception cannot bepropagated using throw onl $

Throw is followed b an instance$

Throw is used within the method$

9ou cannot throw multipleexceptions$

Java throws "e word is used todeclare an exception$

!hec"ed exception can bepropagated with throws$

Throws is followed b class$

Throws is used with the methodsignature$

9ou can declare multiple exceptionse$g$public void method68throws& Exception,()*Exception$

ifference between throw and throws


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Exception handling with method overriding

There are man rules if we tal" about methodoverriding with exception handling$ The %ulesare as

followsI"f the superclass ethod does not declare an exception

&f the superclass method does not declare an exception, subclass overridden method cannot declare the chec"ed exception but it can declare unchec"ed exception$

import 2ava$io$class arent3 void msg683( stem$out$println6@parent@8 5

5class !hild extends arent3 void msg68throws ArithmeticException3

( stem$out$println6@child@85public static void main6(tring args:;83

arent p


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Exception handling with methodoverriding6!ontd$8

"f the superclass ethod declares an exception&f the superclass method declares an exception, subclass overridden method can declare same,subclass exception or no exception but cannot declare parent exception$ import 2ava$io$class arent3 void msg68throws Exception3( stem$out$println6@parent@8 55

class !hild extends arent3 void msg68throws ArithmeticException3( stem$out$println6@child@8 5

public static void main6(tring args:;83arent p


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!ustom Exception

&f ou are creating our own Exception that is "nown as customexception or user#defined exception$ Java custom exceptions areused to customi e the exception according to user need$- the help of custom exception, ou can have our own exceptionand message$

Example of 2ava custom exception$

class &nvalidAgeException extends Exception3&nvalidAgeException6(tring s83

super6s855


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!ustom Exception 6contd$8

class Test!ustomException 3

static void validate6int age8throws &nvalidAgeException3if6ageB C8throw new &nvalidAgeException6@not valid@8

else( stem$out$println6@welcome to vote@8

5

public static void main6(tring args:;83tr 3

validate6 D8

5catch6Exception m83( stem$out$println6@Exception occuredI @Km8 5

( stem$out$println6@rest of the code$$$@85

5


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Than" 9ou

Presentation on Exceptions in Java.ppt

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