6. Exception Handling

Exception HandlingException Handling
By
Nilesh Dalvi
Lecturer, Patkar-Varde College.Lecturer, Patkar-Varde College.
http://www.slideshare.net/nileshdalvi01
Java and Data StructuresJava and Data Structures

Introduction
• An exception is a condition that is caused by a run-time error in
the program.
– Example: Dividing integer by zero. ( / by zero)
• Java has special mechanism for handling such types of errors.
• Its Exception handling.
• Core advantage of exception handling is to maintain the normal
flow of the application.
• Mechanism performs following tasks:
– Find the problem (Hit the exception)
– Inform that error has occur(Throw the exception)
– Receive the error information(catch the exception)
– Take a correct action (Handle the exception)
Nilesh Dalvi, Lecturer@Patkar-Varde College, Goregaon(W).

Exceptions
Categorized into two types:
• Checked exception:
– Explicitly handle in the code itself with the help of try-catch block.
– Extended from java.lang.Exception class
– e.g.IOException, SQLException etc.
• Unchecked exception:
– Not handle in the program code .
– JVM handles such exceptions.
– Extended from the java.lang.RuntimeException
– e.g. ArithmeticException, NullPointerException,
ArrayIndexOutOfBoundsException etc.

Common Java Exceptions
Exception Description
ClassNotFoundException Class not found.
NoSuchFieldException A requested field does not exist.
NoSuchMethodException A requested method does not exist.

Common Java Exceptions
ArithmeticException Arithmetic error, such as divide-by-zero.
ArrayIndexOutOfBoundsException Array index is out-of-bounds.
ArrayStoreException
Assignment to an array element of an
incompatible type.
ClassCastException Invalid cast.
IndexOutOfBoundsException Some type of index is out-of-bounds.
NullPointerException Invalid use of a null reference.
NumberFormatException
Invalid conversion of a string to a
numeric format.
StringIndexOutOfBounds
Attempt to index outside the bounds of
a string.

try and catch block
• Enclose the code that might throw an exception in try block.
• It must be used within the method and must be followed by
either catch or finally block.
• Syntax of try with catch block
• Syntax of try with finally block
try{
...
}catch(Exception_class_Name reference)
{}
try{
...
}finally
{}

try and catch block
class Testtrycatch
{
public static void main(String args[])
{
int data = 50/0;
System.out.println("rest of the code...");
}
}
Output:Exception in thread main java.lang.ArithmeticException:/ by zero

try and catch block
class Testtrycatch
{
{
try{
int data=50/0;
}
catch(ArithmeticException e)
{
System.out.println(e);
}
}
}
Output:Exception in thread main java.lang.ArithmeticException:/ by zero
rest of the code...

Multiple Catch blocks
class MultipleCatch
{
public static void main(String argv[])
{
int num1 = 10;
int num2 = 0;
int result = 0;
int arr[] = new int[5];
try
{
arr[0] = 0;
arr[1] = 1;
arr[2] = 2;
arr[3] = 3;
arr[4] = 4;
arr[5] = 5;
result = num1 / num2;
System.out.println("Result of Division : " + result);
}catch (ArithmeticException e) {
System.out.println("Err: Divided by Zero");
}catch (ArrayIndexOutOfBoundsException e) {
System.out.println("Err: Array Out of Bound");
}
}
}

Nested try…block
class NestedTryBlock
{
{
try{
try{
System.out.println("going to divide");
int b =39/0;
}catch(ArithmeticException e){
}
try{
int a[]=new int[5];
a[5]=4;
}catch(ArrayIndexOutOfBoundsException e)
{
System.out.println(e);}
System.out.println("other statement);
}catch(Exception e){System.out.println("handeled");}
System.out.println("normal flow..");
}
}

finally
• The finally block is a block that is always executed.
• It is mainly used to perform some important tasks such
as closing connection, stream etc.

finally
class FinallyBlock
{
{
try{
int data=25/0;
System.out.println(data);
}
catch(ArithmeticException e){
}
finally{
System.out.println("finally block is
always executed");
}
}
}
Output: Exception in thread main java.lang.ArithmeticException:/ by zero
finally block is always executed
rest of the code...

throw
• The throw keyword is used to explicitly throw an
exception.
• We can throw either checked or uncheked exception.
• The throw keyword is mainly used to throw custom
exception.

throws
throws clause is used to handle the exception thrown by methods
in program.
void method_name() throws exception_class_name
{
...
}

6. Exception Handling

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6. Exception Handling