Exception

What is exception

An unwanted event/situation that disturbs normal flow of program is called exception.

OR

A situation Occurs where our program get terminated

		Exception Handling
-----------------
A situation Occurs where our program get terminated so rest program is not executed
in oreder to execute this program
we have to handle it

By using try  catch Block we can handle 
Exception

Thats is Called Exception Handling

We cant Repair Exception
But We can Handle it with help try and catch

Exception Handling
try
catch
throws
finally
throw


try{
	// Risky Buggy  Guarded Code
}catch()
{
	
}

What is the Hierachy Of Exception

			 Object
			   |
			Throwable
			   |
	---------------------------------							  
                                   
Exception                           Error
	|							  	 |        
	|- IOException                   |-StackOverFlowError
	|- SQLException                  |-VirtualMachineError
	|- ClassNotFoundException        |-OutOfMemoryError
	|-RunTimeException
		|
		|- ArithmaticException
		|-NullPointerException
		|- IndexOutOfBoundException
		|			|
		|			| -ArrayIndexOutOfBoundException

    
Error
-----

+ Errors are non recoverable
+ Errors Occur due to lack of system resorces
+ Ex- VMError, StackOverFlowError,OutOfMemoryError

package p2;

// java.lang.StackOverflowError
public class Demo {
	int j;
	int k;
	int m;

	public static void main(String[] args) {

		try {
			// main(args);
		} catch (Exception e) {

		}

	}

}

	(RumtimeException are implicitely propageted)

Exception are of 2 Types:

+Checked Exception :
--------------------------
* These are the exception checked at compile time.
*Its mandatoty to hadle


+Unchecked Exception : 
---------------------
[is a exception which are unable to checkk at compile time]
These are occured at run time.
All RunTimeExceptions are Unchecked Exception



Checked Exception


	File f=new File("ABC.txt");

	f.createNewFile();

// Note
error: unreported exception IOException; must be caught or declared to be thrown
                f.createNewFile();


*** Problem *****

package p3;

import java.io.File;
import java.io.IOException;

public class Test {
	
	public static void main(String[] args) throws IOException{
		
		f1();
		
	}

	private static void f1() throws IOException {
		
		File f=new File("ABC.txt");
		/*try {
				f.createNewFile();
		}catch(IOException e) {
			
		}*/
		
		f.createNewFile();
		
		System.out.println("Cool");
	}

}


*************************************

package p3;

import java.io.File;
import java.io.IOException;

public class Test {
	
	public static void main(String[] args) {
		/*
		try {
		f1();
		}catch(InterruptedException | IOException e)
		{
			
		}
		*/
		
		try {
			f1();
		}catch (Exception e) {  // Generic Exception
			
		}
		
		
		
	}

	private static void f1() throws InterruptedException, IOException  {
		
		Thread.sleep(5000);  //InterrputedException
		
		
		File f=new File("ABC.txt");

		f.createNewFile(); // IOException

		System.out.println("Cool");
	}

}

***********************************

We can use throws keyword with function
for ex

private static void f1() throws InterruptedException, IOException

we can throws multiple Exception.

*************************************
throw
------
By using throw we can rethrow exception
for ex throw new ArithmeticException();

and we can throw only one exception at a time.


Best Case to Use Throw keyword to create our 
own Exception


---------------------------------------------

finally
------------- 
It is Block
This Block Always Executes.

** we have to use finally with
try with finally
try{
	
}finally{
	
}
or
try catch finally
try{
	
}catch(){

}finally{
	
}

Only one case finally block not executed
System.exit(0);


----------------------------------------------

try with Resources

package p5;

import java.util.InputMismatchException;
import java.util.Scanner;

// try with resources
public class Test {
	
	public static void main(String[] args) {
		
		int n;
		
		/*
		 * Scanner sc=new Scanner(System.in); n=sc.nextInt(); System.out.println(n);
		 */
	
		
		try(Scanner sc1=new Scanner(System.in);){
			
			System.out.println("Enter num");
			n=sc1.nextInt();

			System.out.println(n);
			
		}catch (InputMismatchException e) {
		}		
		
	}

}


************************************
Exception Propagation Means
Delegate Responsibility of exception to calller

*******Customized Exception***********

package p6;

import java.util.Scanner;

class InvalidAge extends RuntimeException {


	public InvalidAge(String s) {
		super(s);
		
	}

	

}

public class Test {

	public static void main(String[] args) {

		int age;
		System.out.println("Enter Age");
		Scanner sc = new Scanner(System.in);
		age = sc.nextInt();

		checkAge(age);

	}

	private static void checkAge(int age) {

		if (age < 18) {
			try {
				throw new InvalidAge("Invalid Age Below 18");
			} catch (InvalidAge e) {
				System.out.println(e.getMessage());
			}
		} else {

			System.out.println("Perfect Age");
		}

	}

}