new Constraint (C# Reference)
The new constraint specifies that any type argument in a generic class declaration must have a public parameterless constructor. To use the new constraint, the type cannot be abstract.
Apply the new constraint to a type parameter when your generic class creates new instances of the type, as shown in the following example:
When you use the new() constraint with other constraints, it must be specified last:
For more information, see the C# Language Specification. The language specification is the definitive source for C# syntax and usage.