We have seen built-in exception classes at various places. However, you often like to raise an exception when the business rule of your application gets violated. So, for this you can create a custom exception class by deriving Exception or ApplicationException class.
The .Net framework includes ApplicationException class since .Net v1.0. It was designed to use as a base class for the custom exception class. However, Microsoft now recommends Exception class to create a custom exception class.
For example, create InvalidStudentNameException class in a school application, which does not allow any special character or numeric value in a name of any of the students.
Example: ApplicationException
class Student
{
public int StudentID { get; set; }
public string StudentName { get; set; }
}
[Serializable]
class InvalidStudentNameException : Exception
{
public InvalidStudentNameException()
{
}
public InvalidStudentNameException(string name)
: base(String.Format("Invalid Student Name: {0}", name))
{
}
}
Now, you can raise InvalidStudentNameException in your program whenever the name contains special characters or numbers. Use the throw keyword to raise an exception.
Example: throw custom exception
class Program
{
static void Main(string[] args)
{
Student newStudent = null;
try
{
newStudent = new Student();
newStudent.StudentName = "James007";
ValidateStudent(newStudent);
}
catch(InvalidStudentNameException ex)
{
Console.WriteLine(ex.Message );
}
Console.ReadKey();
}
private static void ValidateStudent(Student std)
{
Regex regex = new Regex("^[a-zA-Z]+$");
if (regex.IsMatch(std.StudentName))
throw new InvalidStudentNameException(std.StudentName);
}
}
Output:
Invalid Student Name: James000
Thus, you can create custom exception classes to differentiate from system exceptions.
Points to Remember :
Exception is a base class for any type of exception class in C#.
Derive Exception class to create your own custom exception classes.
