C# Keywords Tutorial Part 56: null

A crucial idea in Microsoft’s well-known object-oriented programming language C# is the “null” keyword. It is a unique value that stands in for an uninitialized reference to an object or the lack of any value. We will go through the fundamentals of the C# “null” keyword and its practical applications in this blog article.

What is the “null” keyword?

In C#, the “null” keyword is a literal value that represents a null reference, meaning that the variable does not point to an object in memory. It is the default value for reference types, such as classes, interfaces, and delegates. In contrast, value types, such as integers and booleans, cannot be assigned a null value.

When a variable is declared but not initialized, its value is automatically set to null. For example:

string myString; // implicitly set to null

You can also explicitly assign a null value to a variable using the “null” keyword:

string myString = null;

In addition, you can use the “??”, or null-coalescing operator, to provide a default value for a null reference:

string myString = null;
string myOtherString = myString ?? "default value"; // myOtherString will be "default value"

Why is the “null” keyword important?

The “null” keyword is important because it helps prevent runtime errors caused by uninitialized variables. If you try to access a member of a null reference, such as a property or a method, you will get a “NullReferenceException” at runtime:

string myString = null;
int length = myString.Length; // throws a NullReferenceException

To avoid this, you can check if a reference is null before using it:

string myString = null;
if (myString != null)
{
    int length = myString.Length;
}

In addition, the “null” keyword is often used in C# to indicate that a method or property may return null. For example, the “Find” method of the List<T> class returns null if the element is not found:

List<string> myList = new List<string>() { "foo", "bar", "baz" };
string foundString = myList.Find(s => s.StartsWith("qux")); // returns null