New Constraint

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:

 class ItemFactory<T> where T : new()
    {
        public T GetNewItem()
        {
            return new T();
        }
    }

When you use the new() constraint with other constraints, it must be specified last:

 public class ItemFactory2<T> where T : IComparable, new()
    {
    }

public class MyClass<T> where T : new()
{
    protected T GetObject()
    {
        return new T();
    }
}

T could be a class that does not have a default constructor: in this case new T() would be an invalid statement. The new() constraint says that T must have a default constructor, which makes new T() legal.

You can apply the same constraint to a generic method:

public static T GetObject<T>() where T : new()
{
    return new T();
}

If you need to pass parameters:

protected T GetObject(params object[] args)
{
    return (T)Activator.CreateInstance(typeof(T), args);
}