Exception handling in JAVA

Exception Handling
in JAVA
By – Kunal Singh
Jaskaran Singh
CLASS PRESENTATION

What is Exception?
• An exception is a problem that arises during the
execution of a program. When an Exception occurs the
normal flow of the program is disrupted and the
program terminates abnormally
• Exception Handling is a mechanism to handle runtime
errors.

Situations in which exception
can occur :-
• User entering invalid data.
• Opening a non-existing file.
• Network connections problem.
• Number format exception.

Types of Exception
• Checked exceptions − A checked exception is an
exception that occurs at the compile time, these are also
called as Compile time exceptions.
• Unchecked exceptions − An unchecked exception is an
exception that occurs at the time of execution. These are
also called as Runtime Exceptions.
• Errors − These are not exceptions at all, but problems
that arise beyond the control of the user or the
programmer. e.g. OutOfMemoryError,
VirtualMachineError.

Try-Catch Block
• Try block- It is used to enclose
the code that might throw an
exception. It must be used within
the method.
• Catch block- It is used to handle
the Exception. It must be used
after the try block only. It involves
declaring the type of exception
you are trying to catch.
Syntax:-
try
{
// Protected code
}
catch(ExceptionName e)
{
// Catch block
}

Example (without exception handling)
public class Testtrycatch1{
public static void main(String args[]){
int data=50/0;
System.out.print("rest ");
System.out.print(“of");
System.out.print(“the");
System.out.print(“code");
}
}
Output- Exception in thread main
java.lang.ArithmeticException:/ by zero

Example (with exception handling)
public class Testtrycatch2{
try{
int data=50/0;
}
catch(ArithmeticException e)
{ System.out.println(e);
}
System.out.println("rest of the code...");
} }
rest of the code...

Multiple Catch Block
public class TestMultipleCatchBlock{
try{
int a[]=new int[5];
a[5]=30/0;
}
catch(ArithmeticException e){System.out.println(“e");}
catch(ArrayIndexOutOfBoundsException e){System.out.println(“e");}
System.out.println("rest of the code..."); }
}
rest of the code...

Some common Sub-Classes of exception
are:-
• ArithmeticException - If we divide any number by
zero, there occurs an ArithmeticException
int a=50/0;
• NullPointerException - If we have null value in any
variable, performing any operation by the variable
occurs an NullPointerException.
String s=null;
System.out.println(s.length());

• ArrayIndexOutOfBoundsException - If we are
inserting any value in the wrong index, it would
result ArrayIndexOutOfBoundsException.
int a[]=new int[5];
a[10]=50;
• NumberFormatException- The wrong formatting
of any value, may occur NumberFormatException.
String s="abc";
int i=Integer.parseInt(s);

Finally block
• Finally block is a block
that is used to execute
important code.
• It is always executed
whether exception is
handled or not.
• The finally block follows
a try block or a catch
block.
try {
// Protected code
}
catch (ExceptionType1 e1)
{ // Catch block
}
{ // Catch block
}
{ // Catch block
}
finally
{
// The finally block always
executes.
}

Example
public class TestFinallyBlock2{
try{
int data=25/0;
System.out.println(data); }
catch(ArithmeticException e){
System.out.println(e);}
finally{
System.out.println("finally block will execute");}
} }
Output:Exception in thread main
finally block will execute

User defined exception
• If you are creating your own Exception that is
known as custom exception or user-defined
exception.
• All exceptions must be a child of Throwable.

Throw keyword
• Java throw keyword is used to explicitly throw
an exception.
• We can throw either checked or uncheked
exception in java by throw keyword.
• The throw keyword is mainly used to throw user
defined exception.
Syntax:- throw exception;

Throws Keyword
• The throws keyword is used to declare an exception.
• It gives an information to the programmer that there
may occur an exception so it is better for the
programmer to provide the exception handling code so
that normal flow can be maintained.
• Syntax:-
return_type method_name() throws exception_class_name{
//method code }

Difference between throw and
throws in Java

Exception handling in JAVA

In this document