Csharp/CSharp Tutorial/Operator/is

"is" operator for value data type: int, long and float

<source lang="csharp">class MainClass {

 public static void Main()
 {
   int myInt = 0;
   bool compatible = myInt is int;
   System.Console.WriteLine("myInt is int = " + compatible);
   compatible = myInt is long;
   System.Console.WriteLine("myInt is long = " + compatible);
   compatible = myInt is float;
   System.Console.WriteLine("myInt is float = " + compatible);
 }

}</source>

myInt is int = True
myInt is long = False
myInt is float = False

is operator in class hiearchy

<source lang="csharp">using System;

class A {} class B : A {}

class MainClass {

 public static void Main() { 
   A a = new A(); 
   B b = new B(); 

   if(a is A) 
      Console.WriteLine("a is an A"); 
   if(b is A)  
     Console.WriteLine("b is an A because it is derived from A"); 
   if(a is B)  
     Console.WriteLine("This won"t display -- a not derived from B"); 
   if(b is B) 
     Console.WriteLine("B is a B"); 
   if(a is object) 
     Console.WriteLine("a is an object"); 
 } 

}</source>

a is an A
b is an A because it is derived from A
B is a B
a is an object

Test if someObject is, or is derived from, a TextReader using the is operator

<source lang="csharp">using System; using System.IO; class MainClass {

   public static void Main() 
   {
       Object someObject = new StringReader("This is a StringReader");
       
       if (someObject is TextReader) 
       {
           Console.WriteLine(
               "is: someObject is a TextReader or a derived class");
       }
   }

}</source>

is: someObject is a TextReader or a derived class

Type operators: Is

Testing a Type with "is".

You can determine whether an object is of a certain type by using the "is" operator.

Its general form is shown here:

<source lang="csharp">expr is type</source>

Use is in Console.WriteLine

<source lang="csharp">using System; public class MainClass {

   static void Main() {
       String derivedObj = "Dummy";
       Object baseObj1 = new Object();
       Object baseObj2 = derivedObj;
       Console.WriteLine( "baseObj2 {0} String", baseObj2 is String ? "is" : "isnot" );
       Console.WriteLine( "baseObj1 {0} String", baseObj1 is String ? "is" : "isnot" );
       Console.WriteLine( "derivedObj {0} Object", derivedObj is Object ? "is" : "isnot" );
   }

}</source>

baseObj2 is String
baseObj1 isnot String
derivedObj is Object

Use "is" to avoid an invalid cast.

<source lang="csharp">using System;

class A {} class B : A {}

class CheckCast {

 public static void Main() { 
   A a = new A(); 
   B b = new B(); 

   if(a is B)
     b = (B) a; 
 } 

}</source>

Working with Interfaces: is operator

<source lang="csharp">using System; interface Printable {

   void MarginX(float factor);
   void MarginY(float factor);

} public class Component {

   public Component() {}

} public class TextField: Component, Printable {

   public TextField(string text)
   {
       this.text = text;
   }
   // implementing Printable.MarginX()
   public void MarginX(float factor)
   {
       Console.WriteLine("MarginX: {0} {1}", text, factor);
       // scale the object here.
   }
   
   // implementing Printable.MarginY()
   public void MarginY(float factor)
   {
       Console.WriteLine("MarginY: {0} {1}", text, factor);
       // scale the object here.
   }
   
   private string text;

} class Test {

   public static void Main()
   {
       Component[] dArray = new Component[100];
       
       dArray[0] = new Component();
       dArray[1] = new TextField("A");
       dArray[2] = new TextField("B");
       
       foreach (Component d in dArray)
       {
           if (d is Printable)
           {
               Printable scalable = (Printable) d;
               scalable.MarginX(0.1F);
               scalable.MarginY(10.0F);
           }
       }
   }

}</source>

MarginX: A 0.1
MarginY: A 10
MarginX: B 0.1
MarginY: B 10