Nullable Class

Supports a value type that can be assigned null. This class cannot be inherited.

Namespace:   System
Assembly:  mscorlib (in mscorlib.dll)

public static class Nullable
public ref class Nullable abstract sealed 
type Nullable = class end
Public NotInheritable Class Nullable
System_CAPS_pubmethod System_CAPS_static Compare

Compares the relative values of two Nullable objects.

System_CAPS_pubmethod System_CAPS_static Equals

Indicates whether two specified Nullable objects are equal.

System_CAPS_pubmethod System_CAPS_static GetUnderlyingType

Returns the underlying type argument of the specified nullable type.


A type is said to be nullable if it can be assigned a value or can be assigned null, which means the type has no value whatsoever. By default, all reference types, such as String, are nullable, but all value types, such as Int32, are not.

In C# and Visual Basic, you mark a value type as nullable by using the ? notation after the value type. For example, int? in C# or Integer? in Visual Basic declares an integer value type that can be assigned null.

The Nullable class provides complementary support for the Nullable structure. The Nullable class supports obtaining the underlying type of a nullable type, and comparison and equality operations on pairs of nullable types whose underlying value type does not support generic comparison and equality operations.

Boxing and Unboxing

When a nullable type is boxed, the common language runtime automatically boxes the underlying value of the Nullable object, not the Nullable object itself. That is, if the property is true, the contents of the property is boxed. If the HasValue property is false, null is boxed. When the underlying value of a nullable type is unboxed, the common language runtime creates a new Nullable structure initialized to the underlying value.

Version Information
Universal Windows Platform
Available since 4.5
.NET Framework
Available since 2.0
Portable Class Library
Supported in: portable .NET platforms
Available since 2.0
Windows Phone Silverlight
Available since 7.0
Windows Phone
Available since 8.1
Thread Safety

Any public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe.

Return to top