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VB.NET Nullable

Use nullables to allow an integer to be null. Call GetValueOrDefault and use the Value property.

Nullable. Consider an Integer in VB.NET. It cannot be null—it can only have a numeric value. But we can wrap the Integer inside a nullable Structure, which can logically be Nothing.NothingStructure

With properties and functions, we can test a Nullable. We specify a nullable type by adding a question mark after the type name. For the value, we can access Value.Property

An example. Here we see a nullable Integer named "element." We use the Integer in various ways. We use the Nothing value to indicate "null" in the VB.NET language.

HasValue: This property returns true or false. It indicates whether an underlying value is contained in the nullable.

Boolean

GetValueOrDefault: This function safely returns the underlying value. If the nullable has no value, it returns the value type's default.

Value: This property will throw an exception if the nullable has no value. Prefer GetValueOrDefault to avoid exceptions.

VB.NET program that uses nullable integer Module Module1 Sub Main() ' A nullable can be Nothing. Dim element As Integer? = Nothing Console.WriteLine("HASVALUE: {0}", element.HasValue) Console.WriteLine("GETVALUEORDEFAULT: {0}", element.GetValueOrDefault()) ' Use an Integer value for the nullable Integer. element = 100 Console.WriteLine("VALUE: {0}", element.Value) Console.WriteLine("GETVALUEORDEFAULT: {0}", element.GetValueOrDefault()) End Sub End Module Output HASVALUE: False GETVALUEORDEFAULT: 0 VALUE: 100 GETVALUEORDEFAULT: 100

Notes, null. In VB.NET the keyword "Nothing" is used to indicate null. This makes types like nullable somewhat confusing, because they are based on C# terms.

A summary. What is a null Integer or other null value type? A null thing can be used to indicate an uninitialized value—we can have uninitialized, or an actual number set.

In this way, nullable types can help eliminate ambiguous parts of programs. We do not need to use -1 as a special value meaning "not set." We can use null.
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