Class 17 Exception

8/4/2019 Class 17 Exception

1/15

Object Oriented Programmingwww.ru.ac.bd/cse/~az

Object OrientedProgramming

With Java


2/15

Object Oriented Programingwww.ru.ac.bd/cse/~az

2

Exception Handling

Exception ?

Instance that does not follow a rule

Error


3/15


3

Exception Handling

Suppose an error occurs while a Java program is running.

The error might be caused by

a file containing wrong information,

a flaky network connection, or

use of an invalid array index or

an attempt to use an object reference that hasn't yet been assignedto an object.


4/15


4

Exception Handling

If an operation cannot be completed because of an error, theprogram ought to either:

Return to a safe state and enable the user to execute other

commands;

or

Allow the user to save all his or her work and terminate the program

gracefully.

This may not be easy to do,


5/15


5

Exception Handling

The mission of exception handling is to transfer control

fromwhere the error occurred

toan error-handler that can deal with the situation.

To handle exceptional situations

you must take into account the errors and problems thatmay occur.

What sorts of problems do you need toconsider?


6/15


6

Exception Handling

What sorts of problems do you need toconsider?

User input errors

Int

char


7/15


7

Exception Handling


8/15


8


9/15


9

Exception Handling

To catch an exception,

you set up a try/catch block.

The simplest form of the try block is as follows:


10/15


10

Exception Handling

If any of the code inside the try block throws an exception of theclass specified in the catch clause, then,

1. The program skips the remainder of the code in the try block;

2. The program executes the handler code inside the catch clause.


11/15


11

Exception Handling

If none of the code inside the try block throws an exception, then

the program skips the catch clause.

If any of the code in a method throws an exception of a typeother than the one named in the catch clause,

this method exits immediately.


12/15


12


13/15


13

Exception Handling


14/15


14

finally block

Programs that obtain certain types of resources must return them~ to avoid ~ resource leaks


15/15


15

Exception Handling

Java guarantees that

a finally block will execute whether or not an exception is thrown in thecorresponding try block or any of its corresponding catch blocks.

Java also guarantees that

a finally block (if one is present) will execute if a try block exits by using a return, break or continue statement.

The finally block will notexecute if the application exits early froma try block by calling method System.exit.

Immediately terminates an application.

Documents

Class 17 Exception