Exception handling in Java allows programs to gracefully deal with errors and unexpected conditions. There are two types of exceptions: checked exceptions which must be explicitly caught, and unchecked exceptions which do not need to be caught. The try-catch block is used to catch exceptions, where code that might throw an exception is placed in the try block and catch blocks handle specific exceptions. Finally blocks are always executed and can be used to perform cleanup tasks. Exceptions can also be explicitly thrown using the throw keyword or declared as thrown from methods using the throws clause.

1. 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

2. 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).

3. 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.
Nilesh Dalvi, Lecturer@Patkar-Varde College, Goregaon(W).

4. Common Java Exceptions
Nilesh Dalvi, Lecturer@Patkar-Varde College, Goregaon(W).
Exception Description
ClassNotFoundException Class not found.
NoSuchFieldException A requested field does not exist.
NoSuchMethodException A requested method does not exist.
Exception Description

5. Common Java Exceptions
Nilesh Dalvi, Lecturer@Patkar-Varde College, Goregaon(W).
Exception Description
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.

6. 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
Nilesh Dalvi, Lecturer@Patkar-Varde College, Goregaon(W).
try{
...
}catch(Exception_class_Name reference)
{}
try{
...
}finally
{}

7. try and catch block
Nilesh Dalvi, Lecturer@Patkar-Varde College, Goregaon(W).
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

8. try and catch block
Nilesh Dalvi, Lecturer@Patkar-Varde College, Goregaon(W).
class Testtrycatch
{
public static void main(String args[])
{
try{
int data=50/0;
}
catch(ArithmeticException e)
{
System.out.println(e);
}
System.out.println("rest of the code...");
}
}
Output:Exception in thread main java.lang.ArithmeticException:/ by zero
rest of the code...

9. Multiple Catch blocks
Nilesh Dalvi, Lecturer@Patkar-Varde College, Goregaon(W).
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");
}
}
}

10. Nested try…block
Nilesh Dalvi, Lecturer@Patkar-Varde College, Goregaon(W).
class NestedTryBlock
{
public static void main(String args[])
{
try{
try{
System.out.println("going to divide");
int b =39/0;
}catch(ArithmeticException e){
System.out.println(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..");
}
}

11. 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.
Nilesh Dalvi, Lecturer@Patkar-Varde College, Goregaon(W).

12. finally
Nilesh Dalvi, Lecturer@Patkar-Varde College, Goregaon(W).
class FinallyBlock
{
public static void main(String args[])
{
try{
int data=25/0;
System.out.println(data);
}
catch(ArithmeticException e){
System.out.println(e);
}
finally{
System.out.println("finally block is
always executed");
}
System.out.println("rest of the code...");
}
}
Output: Exception in thread main java.lang.ArithmeticException:/ by zero
finally block is always executed
rest of the code...

13. 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.
Nilesh Dalvi, Lecturer@Patkar-Varde College, Goregaon(W).

14. throws
throws clause is used to handle the exception thrown by methods
in program.
void method_name() throws exception_class_name
{
...
}
Nilesh Dalvi, Lecturer@Patkar-Varde College, Goregaon(W).

15. Q & A