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See Also
NullityThe null keyword is a literal that represents a null reference, one that does not refer to any object. null is the default value of reference-type variables. Ordinary value types cannot be null, except for nullable value types.
The following example demonstrates some behaviors of the null keyword:
class Program{ class MyClass { public void MyMethod() { } } static void Main() { // Set a breakpoint here to see that mc = null. // However, the compiler considers it "unassigned." // and generates a compiler error if you try to // use the variable. MyClass mc; // Now the variable can be used, but... mc = null; // ... a method call on a null object raises // a run-time NullReferenceException. // Uncomment the following line to see for yourself. // mc.MyMethod(); // Now mc has a value. mc = new MyClass(); // You can call its method. mc.MyMethod(); // Set mc to null again. The object it referenced // is no longer accessible and can now be garbage-collected. mc = null; // A null string is not the same as an empty string. string s = null; string t = String.Empty; // Logically the same as "" // Equals applied to any null object returns false. Console.WriteLine("t.Equals(s) is {0}", t.Equals(s)); // Equality operator also returns false when one // operand is null. Console.WriteLine("Empty string {0} null string", s == t ? "equals": "does not equal"); // Returns true. Console.WriteLine("null == null is {0}", null == null); // A value type cannot be null // int i = null; // Compiler error! // Use a nullable value type instead: int? i = null; // Keep the console window open in debug mode. }}C# language specification
For more information, see the C# Language Specification. The language specification is the definitive source for C# syntax and usage.
