Csharp/C Sharp/Language Basics/is

choose between two overloaded methods at run-time using the "is" keyword

 
using System;
public class BankAccount {
    virtual public void Withdraw() {
        Console.WriteLine("Call to BankAccount.Withdraw()");
    }
}
public class SavingsAccount : BankAccount {
    override public void Withdraw() {
        Console.WriteLine("Call to SavingsAccount.Withdraw()");
    }
}
public class MainClass {
    public static void Main(string[] strings) {
        BankAccount ba = new BankAccount();
        Test(ba);
        SavingsAccount sa = new SavingsAccount();
        Test(sa);
    }
    public static void Test(BankAccount baArgument) {
        if (baArgument is SavingsAccount) {
            SavingsAccount saArgument = (SavingsAccount)baArgument;
            saArgument.Withdraw();
        } else {
            baArgument.Withdraw();
        }
    }
}

is Checker

 
using System;
using System.Collections.Generic;
using System.Text;
class Checker {
    public void Check(object param1) {
        if (param1 is ClassA)
            Console.WriteLine("Variable can be converted to ClassA.");
        else
            Console.WriteLine("Variable can"t be converted to ClassA.");
        if (param1 is IMyInterface)
            Console.WriteLine("Variable can be converted to IMyInterface.");
        else
            Console.WriteLine("Variable can"t be converted to IMyInterface.");
        if (param1 is MyStruct)
            Console.WriteLine("Variable can be converted to MyStruct.");
        else
            Console.WriteLine("Variable can"t be converted to MyStruct.");
    }
}
interface IMyInterface {
}
class ClassA : IMyInterface {
}
class ClassB : IMyInterface {
}
class ClassC {
}
class ClassD : ClassA {
}
struct MyStruct : IMyInterface {
}
class Program {
    static void Main(string[] args) {
        Checker check = new Checker();
        ClassA try1 = new ClassA();
        ClassB try2 = new ClassB();
        ClassC try3 = new ClassC();
        ClassD try4 = new ClassD();
        MyStruct try5 = new MyStruct();
        object try6 = try5;
        Console.WriteLine("Analyzing ClassA type variable:");
        check.Check(try1);
        Console.WriteLine("\nAnalyzing ClassB type variable:");
        check.Check(try2);
        Console.WriteLine("\nAnalyzing ClassC type variable:");
        check.Check(try3);
        Console.WriteLine("\nAnalyzing ClassD type variable:");
        check.Check(try4);
        Console.WriteLine("\nAnalyzing MyStruct type variable:");
        check.Check(try5);
        Console.WriteLine("\nAnalyzing boxed MyStruct type variable:");
        check.Check(try6);
        Console.ReadKey();
    }
}

The is operator confirms that the employee is a manager.

 
using System;

public class Starter {
    public static void Main() {
        Manager person = new Manager("Accounting");
        Console.WriteLine("[Menu]\n");
        Console.WriteLine("Task 1");
        Console.WriteLine("Task 2");
        if (person is IManager) {
            IManager mgr = person;
            Console.WriteLine("\n[{0} Menu]\n",mgr.Department);
            Console.WriteLine("Task 3");
        }
    }
}
public interface IManager {
    string Department {
        get;
    }
}
public class Employee {
}
public class SalariedEmployee : Employee {
}
public class Manager : SalariedEmployee, IManager {
    public Manager(string dept) {
        propDepartment = dept;
    }
    private string propDepartment;
    public string Department {
        get {
            return propDepartment;
        }
    }
}

Using the is Keyword to Work with an Interface

 

using System;
   
public interface IPrintMessage
{
    void Print();
};
   
class Class1
{
    public void Print()
    {
        Console.WriteLine("Hello from Class1!");
    }
}
   
class Class2 : IPrintMessage
{
    public void Print()
    {
        Console.WriteLine("Hello from Class2!");
    }
}
   
class MainClass
{
    public static void Main()
    {
        PrintClass   PrintObject = new PrintClass();
   
        PrintObject.PrintMessages();
    }
}
   
class PrintClass
{
    public void PrintMessages()
    {
        Class1      Object1 = new Class1();
        Class2      Object2 = new Class2();
   
        PrintMessageFromObject(Object1);
        PrintMessageFromObject(Object2);
    }
   
    private void PrintMessageFromObject(object obj)
    {
        if(obj is IPrintMessage)
        {
            IPrintMessage PrintMessage;
   
            PrintMessage = (IPrintMessage)obj;
            PrintMessage.Print();
        }
    }
}