C# - throw keyword:

We have seen in the previous section how to handle exceptions which are automatically raised by CLR. Here, we will see how to raise an exception manually.

An exception can be raised manually by using the throw keyword. Any type of exceptions which is derived from Exception class can be raised using the throw keyword.

static void Main(string[] args)
{
    Student std = null;

    try
    {
        PrintStudentName(std);
    }
    catch(Exception ex)
    {
        Console.WriteLine(ex.Message );
    }                      

    Console.ReadKey();
}

private static void PrintStudentName( Student std)
{
    if (std  == null)
        throw new NullReferenceException("Student object is null.");
        
    Console.WriteLine(std.StudentName);
}

In the above example, PrintStudentName() method raises NullReferenceException if Student object is null.

Please notice that throw creates an object of any valid exception type using the new keyword. The throw keyword cannot be used with any other type which does not derive from the Exception class.

Learn how to create custom exception type in the next section.