presentation-on-exception-handling-160611180456 (1).pptx

java

1. PRESENTATION ON Exception Handling

2. What is an exception? * An exception is an error condition that changes the normal flow of control in a program * When an Exception occurs the normal flow of the program is disrupted and the program/Application terminates abnormally, which is not recommended, therefore these exceptions are to be handled

3. Why Exception Occurs? An exception can occur for many different reasons, below given are some scenarios where exception occurs. >>A user has entered invalid data. >>A file that needs to be opened cannot be found. >>A network connection has been lost in the middle of communications or the JVM has run out of memory.

4. Exception Hierarchy

5. Exception Has two Main classes : 1. Checked exceptions : known as compile time exceptions. Programmer should take care of (handle) these exceptions 2. Un c hecked exceptions : Known as Runtime Exceptions. These include programming bugs, such as logic error also.

6. Keyword Description try The "try" keyword is used to specify a block where we should place an exception code. It means we can't use try block alone. The try block must be followed by either catch or finally. catch The "catch" block is used to handle the exception. It must be preceded by try block which means we can't use catch block alone. It can be followed by finally block later. finally The "finally" block is used to execute the necessary code of the program. It is executed whether an exception is handled or not. throw The "throw" keyword is used to throw an exception. throws The "throws" keyword is used to declare exceptions. It specifies that there may occur an exception in the method. It doesn't throw an exception. It is always used with method signature.

7. Checked exceptions

8. import java.io.File ; import java.io.FileReader ; public class FilenotFound_Demo { public static void main(String args []){ File file=new File("E://file.txt"); FileReader fr = new FileReader (file); } } Output: C:\>javac FilenotFound_Demo.java FilenotFound_Demo.java:8: error: unreported exception FileNotFoundException ; must be caught or declared to be thrown FileReader fr = new FileReader (file); Example

9. Unchecked exceptions

10. Example public class Unchecked_Demo { public static void main(String args []){ int num []={1,2,3,4}; System.out.println ( num [5]); } } Output: Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException : 5 at Exceptions.Unchecked_Demo.main (Unchecked_Demo.java:8

11. Exception Handling Terms 1.Try – used to enclose a segment of code that may produce a exception 2.Catch – placed directly after the try block to handle one or more exception types 3.Throw – to generate an exception or to describe an instance of an exception 4.Finally – optional statement used after a try-catch block to run a segment of code regardless if a exception is generated

12. Try – Catch Block Try – used to enclose a segment of code that may produce a exception Catch – placed directly after the try block to handle one or more exception types try { statements; } catch(Exception ex) { perform operations before exits ; throw ex; }

13. Multiple catch statements try { <code segment that may throw an exception..> } catch ( IOException e) { System.out.println ( e.getMessage ()); } catch ( FileNotFoundException e ){ System.out.println ( “ FileNotFound ! ” ); }

14. Nested try-catch block try  {        statement  1;            try    {      statement  2 ; statement  3;      }   catch(Exception  e)   {    }   }   catch(Exception  e)  {  }   

15. By using Throw THROW -generate an exception or to describe an instance of an exception Define a class : public class EmptyStackException extends Exception { } Here is how you use the class: public class Stack { public Object Pop() throws EmptyStackException { if (Empty()) throw new EmptyStackException (); ... } } Note that you must use new to create an exception object; you cannot just throw an exception.

16. Example static class Exception2{ static int sum( int num1, int num2){ if (num1 == 0) throw new ArithmeticException ("First parameter is not valid"); else System.out.println ("Both parameters are correct!!"); return num1+num2 ; } public static void main(String args []){ int res=sum(1,12); System.out.println (res); System.out.println ("Continue Next statements"); } }

17. The finally try { statements; } catch(TheExceptionex ) { handling ex; } finally { finalStatements; }

18. Example public static void main(String[] arg ){ try{ int i = 10/0; } catch(Exception ex){ System.out.println ("Inside 1st catch Block"); } finally { System.out.println ("Inside 1st finally block"); } try{ int i = 10/10; } catch(Exception ex){ System.out.println ("Inside 2nd catch Block"); } finally { System.out.println ("Inside 2nd finally block"); } } Inside 1st catch Block Inside 1st finally block Inside 2nd finally block

19. Thanks All