Editing Comparison of C Sharp and Java (section)

=== {{anchor|Nullable types}}Lifted (nullable) types ===
C# allows value/primitive/simple types to be "lifted" to allow the special {{mono|null}} value in addition to the type's native values. A type is lifted by adding a {{code|?}} suffix to the type name; this is equivalent to using the {{code|Nullable<T>}} [[Generic programming|generic]] type, where {{mono|T}} is the type to be lifted. Conversions are implicitly defined to convert between values of the base and the lifted type. The lifted type can be compared against {{mono|null}} or it can be tested for {{mono|HasValue}}. Also, lifted operators are implicitly and automatically defined based on their non-lifted base, where – with the exception of some Boolean operators – a null argument will propagate to the result.

Java does not support type lifting as a concept, but all of the built-in primitive types have corresponding wrapper types, which do support the {{mono|null}} value by virtue of being reference types (classes).

According to the Java spec, any attempt to dereference the {{mono|null}} reference must result in an exception being thrown at run-time, specifically a {{mono|NullPointerException}}. (It would not make sense to dereference it otherwise, because, by definition, it points to no object in memory.) This also applies when attempting to [[Auto-unboxing|unbox]] a variable of a wrapper type, which evaluates to {{mono|null}}: the program will throw an exception, because there is no object to be unboxed – and thus no boxed value to take part in the subsequent computation.

The following example illustrates the different behavior. In C#, the lifted*operator propagates the {{mono|null}} value of the operand; in Java, unboxing the null reference throws an exception.

Not all C# lifted operators have been defined to propagate {{mono|null}} unconditionally, if one of the operands is {{mono|null}}. Specifically, the [[Boolean operator (computer programming)|Boolean operator]]s have been lifted to support [[ternary logic]] thus keeping impedance with [[SQL]].

The Java Boolean operators do not support ternary logic, nor is it implemented in the base class library.