Exception handling in java

Topics : Exception handling in java
created by……
Md .shohel Rana
Roll:140135
2nd year 2nd semester
Dept. of Cse

Exception Handling
An exception is an abnormal condition in which the
normal execution of code gets hampered at run
time.
The error handling mechanism that is called
exception handling.

When occur Exception in a program
Some of the common runtimes errors
1) Dividing a number by zero
2) Accessing an element that is out of bounds of an array
3) Using negative value as array size
4) Converting string to integer
5) File error
6) Corrupting memory

Why we use exception handling macanisum
 Notify the error
 Save all work
 Allow graceful termination of a program

try, catch, finally keywords
the code which might throw some exceptions should be
kept in try block.
the catch block can hava the code to handle the
exception
finally block can be used to clean up code or release
some resources that are utilized in the program

using try,catch and finally keywords
There are three forms of try statement:
1) try-catch
A try block followed by one or more catch blocks.
2) try-finally
A try block followed by a finally blocks.
3) try-catch-finally
A try blocks followed by one or more catch blocks followed by a finally block.

 Syntax:
Try{
//code that might cause an exception is kept here
}catch(ExceptionType obj){
//when an exception occurs, the control comes here
} catch(ExceptionType obj){
}

 Syntax:
Try{
}finally{
//release some resources here
}

 Syntax:
Try{
}catch(ExceptionType obj){
}finally{
//release some resources here
}

try,catch and finally-Rules
 When there is a try block, catch or finally block should be
there
 There should not be any statements between try and catch
and finally
 Finally block is optional.
 Only one finally block for a try block.
 There can be multiple catch blocks for a try block.

Types of Exception
Exception
Built-in
Exception
User-defined
Exception

Some java Pre-defined /Built-in exception class
Java.lang.Exception is a super class for all pre-defined exception class.
1. Exception ---------------------------------------------------> Base class for all exception objects.
2. SystemException------------------------------------------> Base class for all runtime errors.
3. ArithmeticException-------------------------------------> Arithmetic error.
4. ArrayIndexOutOfBoundsException-----------------> array index out of bounds
5. NegativeArraySizeException--------------------------> Array created with a negative size.
6. NullPointerException------------------------------------->invalid use of a null reference.
7. FileNotFoundException---------------------------------> when file is not found
8. ClassNotFoundException----------------------------- >when class is not found
9. NumberFormatException------------------------------> invalid conversion of a string ot a number format

NumberFormatException
1) -----correct
String str1="10";
System.out.println("this is string :"+str1);
int x=Integer.parseInt(str1);
System.out.println("after convart string to int: "+x*x);
2)-----exception
String str2="ten";
int y=Integer.parseInt(str2);
System.out.println("this is string :"+str2);

IndexOutOfBoundsException
-------there are two types………..
1. ArrayIndexOutOfBoundsException
2. StringIndexOutOfBoundsException
……………………………………………..
int [] marks={3,4,5};
System.out.println(marks[4]); //Wrong index number
………………………………………………
String str="hello";
System.out.println(str.charAt(5)); //Wrong character index number

FileNotFoundException
try {
File inputfile=new File("c:file.txt");
FileReader f=new FileReader(inputfile);
}
catch (FileNotFoundException e) {
System.out.println("file not found");
}

User-defined Exceptions
 Most of the times when we are developing an application in java, we
often feel a need to create and throw our own exceptions.These
exceptions are known as user-defined or custom exceptions.
Point ot remember:
1. user-defined exception needs to inherit (extends) Exception class in
order to act as an exception.
2. throw keyword is used to throw such exceptions.

Using super() keyword
Part-1:
class DemoException extends Exception
{
public DemoException(String p)
{
super("i got an exception "+p); //call the main Exception class
}
}

Part-2:
public class userDef {
public static void main(String args[])
{
int balance = 100, withdraw = 1000;
if (balance < withdraw) {
try{
DemoException e = new DemoException("money is short");
throw e; //this throw the main exception class not DemoException class
}
catch(DemoException e) {
System.out.println("insufficient balancenn" + e);
}
}
else {
System.out.println("Draw & enjoy Sir, Best wishes of the day");
} }
}

The End
..………………………………………………………………………………

Exception handling in java

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