Exceptions and Defensive Coding

Throw and Catch

A method can throw an exception and a caller can catch it.

Throw and Catch

ThrowCatch.cs 
using System;

class Program
{
    static string AgeGroup(int age)
    {
        if (age < 0)
        {
            throw new ArgumentException("age");
        }

        if (age < 18)
        {
            return "minor";
        }

        return "adult";
    }

    static void Main()
    {
        int age = ;
        string group = "unknown";

        try
        {
            group = AgeGroup(age);
        }
        catch (ArgumentException)
        {
            group = "invalid";
        }

        Console.WriteLine($"age={age}");
        Console.WriteLine($"group={group}");
    }
}

using System;

class Program
{
    static string AgeGroup(int age)
    {
        if (age < 0)
        {
            throw new ArgumentException("age");
        }

        if (age < 18)
        {
            return "minor";
        }

        return "adult";
    }

    static void Main()
    {
        int age = ;
        string group = "unknown";

        try
        {
            group = AgeGroup(age);
        }
        catch (ArgumentException)
        {
            group = "invalid";
        }

        Console.WriteLine($"age={age}");
        Console.WriteLine($"group={group}");
    }
}

using System;

class Program
{
    static string AgeGroup(int age)
    {
        if (age < 0)
        {
            throw new ArgumentException("age");
        }

        if (age < 18)
        {
            return "minor";
        }

        return "adult";
    }

    static void Main()
    {
        int age = ;
        string group = "unknown";

        try
        {
            group = AgeGroup(age);
        }
        catch (ArgumentException)
        {
            group = "invalid";
        }

        Console.WriteLine($"age={age}");
        Console.WriteLine($"group={group}");
    }
}
throw `throw` reports a problem that the caller should handle.