Java class 7

What is Exception Handling?
• Exception is the one that stops the execution
of the program unexpectedly.
• The process of handling these exceptions is
called Exception Handling.

Exception Handling Mechanism
Exception can be handled in 3 ways:
• try block
• Catch block
• Finally block

Exception Classes
Throwable
Error
Exception
Runtime
Exceptions
Compile – enforced
Exception
Object
1
2

Try and Catch block
try
{
//code where you think exception would occur
}
catch(Exception_Class reference)
{
//Catch the exception and displays that exception
}

Try – Catch example
public class Try_Catch {
public static void main(String[] args) {
int y=0;
try {
System.out.println(5/y);
}
catch(Exception e) {
System.out.println(“Divide By Zero Exception”);
}
}
}

Multiple Catches
• When there is a chance
of getting different
types of exceptions we
use multiple catch
block for a try block.
try
{
//statements
}
{
//statements for one type of exception
}
{
//statements for other type of exception
}

Multiple- Catch Example
package com.edureka.exception.multiplecatch;
class Multiple_Catch {
int n;
int array[]=new int[3];
Multiple_Catch(int n)
{
try{
if(n==0)
System.out.println(5/n);
else{
array[3]=n;
System.out.println(array);
}
}
catch(ArrayIndexOutOfBoundsException
arrayexception)
{
System.out.println(arrayexception);
}
catch(ArithmeticException divideexception)
{
System.out.println(divideexception);
}
}
}

Multiple- Catch Example
package com.edureka.exception.multiplecatch;
class Main {
public static void main(String[] args)
{
Multiple_Catch multiplecatch1= new Multiple_Catch(0);
Multiple_Catch multiplecatch2= new Multiple_Catch(5);
}
}

What is throw keyword?
• throw is a keyword which is used to call the sub class of an
exception class.
• This keyword is also used to throw the exception occurred in try
block to catch block.
try{
throw new Exception_class(“message”);
}
catch(Exception_class reference){
//statements
}

Example using throw keyword
package com.edureka.exception.throwkeyword;
public class Student {
Student(int studentid, String name){
try{
if(studentid==0)
throw new Exception("id can not be zero");
else
System.out.println("The id of "+name+"
is:"+studentid);
}
catch (Exception e) {
System.out.println(e);
}
}
}
package com.edureka.exception.throwkeyword;
public class Main {
public static void main(String[] args) {
Student student1 = new Student(0,"STUDENT1");
Student student2 = new Student(1,"STUDENT2");
}
}

What is throws keyword?
• throws is a keyword applied to methods for
which an exception has raised during its
execution.
returntype method_name throws Exception_Class
{
// statements
}

Example using throws keyword
package com.edureka.throwskeyword;
public class GiveInput {
void takeInput() throws IOException
{
BufferedReader reader=new
BufferedReader(new
InputStreamReader(System.in));
System.out.println("Enter your name");
String name=reader.readLine();
System.out.println("Your name is: "+name);
}
}
package com.edureka.throwskeyword;
public class Main {
public static void main(String[] args) throws
IOException {
GiveInput input=new GiveInput();
input.takeInput();
}
}

Uses of finally keyword
• When we want a set of statements to be executed
even after an exception has occurred then we use
finally block.
• finally
{
//statements that needs to be executed after
exception
}

Types of Exception
• Run-time Exceptions.
• Compile Enforced Exception

Run-Time Exceptions
• Are also called as Unchecked Exception.
• These exceptions are handled at run-time i.e by JVM
after they have occurred by using try and catch
block.
• Eg: ArrayIndexOutOfBoundsException,
ArithmeticException
NullPointerException

Complier-enforced Exceptions
• Are also called as Checked Exceptions.
• These exceptions are handled by java complier
before they occur by using throws keyword.
• Eg: IOException,
FileNotFoundException

User-defined Exceptions
• Across built-in exceptions user can also
define his own exceptions.
• It can be done by defining a class that extends
Exception class and creating a constructor of
the class (user-defined) with string argument
to print that message when exception occurs.

Advantages of Exception
• The program will still execute even if an exception
arises i.e finally block.
• If you can't handle the exception JVM will handle the
exception if we use throws keyword.
• We can differentiate the exceptions that have
occurred.

Errors and Error Handling
 Design-time error: These are the errors that occur while
designing the programs.
Eg: Syntax errors
These errors will be shown with a red mark in eclipse IDE so
that you can easily find and correct it.

Errors and Error Handling
 Logical error: These are the errors done by programmer. The
programs with these errors will run but does not produce
desired results.
Eg: getting division of two numbers as output but expected is
multiplication of numbers.
These errors can be rectified by understanding the logic and
checking whether it is works out correctly or not.

Java class 7

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Java class 7