Exception handling is of 2 types:
- System-level exceptions
- Application-level exceptions
System-level exceptions are the exceptions thrown by the system. These exceptions are thrown by the CLR. E.g. exception thrown due to failure in database connection or network connection.
Application-level exceptions are thrown by user-created applications. E.g. exceptions thrown due to arithmetic operations or referencing any null object.
InvalidCastException Class
using System;
class InvalidCastError
{
static void Main(string[] args)
{
try
{
float numOne = 3.14F;
Object obj = numOne;
int result = (int)obj;
Console.WriteLine("Value of numOne = {0}", result);
}
catch (InvalidCastException objEx)
{
Console.WriteLine("Message : {0} ", objEx.Message);
Console.WriteLine("Error: {0}", objEx);
}
catch (Exception ex)
{
Console.WriteLine(ex);
}
}
}
ArrayTypeMismatchException Class
using System;
class ArrayMisMatch
{
static void Main(string[] args)
{
string[] names = { "James", "Jack", "Peter" };
int[] id = { 10, 11, 12 };
double[] salary = { 1000, 2000, 3000 };
float[] bonus = new float[3];
try
{
salary.CopyTo(bonus, 0);
}
catch (ArrayTypeMismatchException objType)
{
Console.WriteLine("Error: {0}", objType);
}
catch (Exception objEx)
{
Console.WriteLine("Error : {0}", objEx);
}
}
}
NullReferenceException Class
using System;
class Employee
{
private string _empName;
private int _empID;
public Employee()
{
_empName = "David";
_empID = 101;
}
static void Main(string[] args)
{
Employee objEmployee = new Employee();
Employee objEmp = objEmployee;
objEmployee = null;
try
{
Console.WriteLine("Employee Name: " + objEmployee._empName);
Console.WriteLine("Employee ID: " + objEmployee._empID);
}
catch (NullReferenceException objNull)
{
Console.WriteLine("Error: {0}", objNull);
}
catch (Exception objEx)
{
Console.WriteLine("Error : {0}", objEx);
}
}
}
Public Methods of System.Exception Class
using System;
class ExceptionMethods
{
static void Main(string[] args)
{
byte numOne = 200;
byte numTwo = 5, result = 0;
try
{
result = checked((byte)(numOne * numTwo));
Console.WriteLine("Result = {0}", result);
}
catch (Exception objEx)
{
Console.WriteLine("Error Description : {0}", objEx.ToString());
Console.WriteLine("Exception : {0}", objEx.GetType());
}
}
}
Public Properties Of System.Exception class
using System;
class ExceptionMethods
{
static void Main(string[] args)
{
byte numOne = 200;
byte numTwo = 5, result = 0;
try
{
result = checked((byte)(numOne * numTwo));
Console.WriteLine("Result = {0}", result);
}
catch (OverflowException objEx)
{
Console.WriteLine("Message : {0}", objEx.Message);
Console.WriteLine("Source : {0}", objEx.Source);
Console.WriteLine("TargetSite : {0}", objEx.TargetSite);
Console.WriteLine("StackTrace : {0}", objEx.StackTrace);
}
catch (Exception objEx)
{
Console.WriteLine("Error : {0}", objEx.ToString());
}
}
}
Finally Keyword
using System;
class InvalidCastError
{
static void Main(string[] args)
{
try
{
float numOne = 3.14F;
Console.WriteLine("Value of numOne = {0}", numOne);
}
catch (InvalidCastException objEx)
{
Console.WriteLine("Message : {0} ", objEx.Message);
Console.WriteLine("Error: {0}", objEx);
}
catch (Exception ex)
{
Console.WriteLine(ex);
}
finally
{
Console.WriteLine("End of program");
}
}
}
Throw keyword - ArgumentNullException()
using System;
using System.Collections.Generic;
using System.Text;
namespace ConsoleApplication4
{
class Program
{
static void thro(string name)
{
if (name == null)
throw new ArgumentNullException();
else
Console.WriteLine(name);
}
static void Main(string[] args)
{
try
{
string name;
name = null;
thro(name);
}
catch (ArgumentNullException ex)
{
System.Console.WriteLine(ex);
}
}
}
}
Nested try catch
using System;
using System.Collections.Generic;
using System.Text;
namespace ConsoleApplication4
{
class Program
{
static void Main(string[] args)
{
string[] names = { "John", "James" };
int numOne = 0;
int result;
try
{
try
{
result = 133/numOne;
}
catch(ArithmeticException ae)
{
System.Console.WriteLine(ae);
}
names[2] = "aptech";
}
catch(IndexOutOfRangeException ie)
{
System.Console.WriteLine();
System.Console.WriteLine(ie);
}
}
}
}
User defined exception
Example 1
using System;
using System.Collections.Generic;
using System.Text;
namespace ConsoleApplication4
{
class Program : Exception
{
public Program()
{
Console.WriteLine("Age should be between 17 and 100");
}
}
class handleExp
{
public static void Main()
{
int val;
val = Int32.Parse(Console.ReadLine());
try
{
if (val < 17 || val > 100)
{
throw new Program();
}
else
{
Console.WriteLine("welcome to polling booth");
}
}
catch (Program obj)
{
Console.WriteLine(obj.Message);
}
}
}
}
Example 2
using System;
using System.Collections.Generic;
using System.Text;
namespace ConsoleApplication4
{
class Program : Exception
{
public Program(string msg): base(msg)
{
Console.WriteLine("Constructor invoked");
}
}
class handleExp
{
public static void Main()
{
int value;
try
{
value = Int32.Parse(Console.ReadLine());
if (value < 10 || value > 100)
throw new Program("this exception is going to be thrown by the program");
else
Console.WriteLine(value);
}
catch (Program obj)
{
Console.WriteLine(obj.Message);
}
}
}
}
Tester-Doer Pattern
using System;
using System.Collections.Generic;
using System.Text;
namespace ConsoleApplication4
{
class NumberDoer
{
public void Process(int numOne, int numTwo)
{
try
{
if (numTwo == 0)
{
throw new DivideByZeroException("Value of divisor is zero");
}
else
{
Console.WriteLine("Quotient: " + (numOne / numTwo));
Console.WriteLine("Remainder: " + (numOne % numTwo));
}
} catch (DivideByZeroException objDivide)
{
Console.WriteLine("Error {0}: " + objDivide);
}
}
}
class handleExp
{
NumberDoer objDoer = new NumberDoer();
public void AcceptDetails()
{
int dividend = 0;
int divisor = 0;
Console.WriteLine("Enter the value of dividend");
try
{
dividend = Convert.ToInt32(Console.ReadLine());
}
catch (FormatException objForm)
{
Console.WriteLine("Error : {0}" + objForm);
}
Console.WriteLine("Enter the value of divisor:");
try
{
divisor = Convert.ToInt32(Console.ReadLine());
}
catch (FormatException objFormat)
{
Console.WriteLine("Error: {0}" + objFormat);
}
if ((dividend > 0) || (divisor > 0))
{
objDoer.Process(dividend, divisor);
}
else
{
Console.WriteLine("Invalid Input");
}
}
public static void Main()
{
handleExp objTester = new handleExp();
objTester.AcceptDetails();
}
}
}
TryParse Pattern
using System;
using System.Collections.Generic;
using System.Text;
namespace ConsoleApplication4
{
class Product
{
private int _quantity;
private float _price;
private double _sales;
string _productName;
public Product()
{
_productName = "Motherboard";
}
public void AcceptDetails()
{
Console.WriteLine("Enter the number of " + _productName + " sold");
try
{
_quantity = Int32.Parse(Console.ReadLine());
}
catch (FormatException objFormat)
{
Console.WriteLine("Error {0}: " + objFormat);
return;
}
Console.WriteLine("Enter the price of the product");
if (float.TryParse((Console.ReadLine()), out _price) == true)
{
_sales = _price * _quantity;
}
else
{
Console.WriteLine("Invalid price inserted");
}
Console.WriteLine("Product Name: " + _productName);
Console.WriteLine("Product Price: " + _price);
Console.WriteLine("Quantity sold: " + _quantity);
Console.WriteLine("Total Sale Value: " + _sales);
}
static void Main(string[] args)
{
Product objGoods = new Product(); objGoods.AcceptDetails();
}
}
}
System.TypeInitializationException Class
using System;
class TypeInitError
{
static TypeInitError()
{
throw new ApplicationException("This program throws TypeInitializationException error.");
}
static void Main(string[] args)
{
try
{
TypeInitError objType = new TypeInitError();
}
catch (System.TypeInitializationException objEx)
{
Console.WriteLine("ERROR: {0}", objEx);
}
catch (Exception objEx)
{
Console.WriteLine("Error : {0}", objEx);
}
}
}
The throw statement
using System;
class RethrowException
{
static void Main(string[] args)
{
string[] customerNames = new string[3];
int[] age = new int[3];
try
{
try
{
for (int i = 0; i < customerNames.Length; i++)
{
Console.WriteLine("Enter the name of the customer: ");
customerNames[i] = Console.ReadLine();
Console.Write("Enter the age of the Customer:");
age[i] = Convert.ToInt32(Console.ReadLine());
}
}
catch (FormatException objEx)
{
Console.WriteLine("Invalid input");
//throw;
}
}
catch (Exception objEx)
{
Console.WriteLine("Error thrown by the inner catch block caught in the outer catch block");
}
}
}
Custom Exception
using System;
class NewCustom : Exception
{
public NewCustom(string msg) : base(msg)
{
}
static void Main(string[] args)
{
int dividend = 133;
int divisor;
int result = 0;
Console.WriteLine("Enter the value of divisor");
try
{
divisor = Convert.ToInt32(Console.ReadLine());
if (divisor == 0)
{
throw new NewCustom("Zero not allowed here");
}
if (divisor < 0)
{
throw new NewCustom("Please enter a positive number");
}
Console.WriteLine("You entered: " + divisor.ToString());
result = dividend / divisor;
}
catch (NewCustom objEx)
{
Console.WriteLine("Error :" + objEx.Message);
}
Console.WriteLine("Result of division: " + result);
}
}
