As mentioned in Web Services and Null Values – Part I-II one should not return a Java wrapper type, e.g. Boolean, from a Web Service as this type is modeled as xsd:boolean in the WSDL file.
If the service returns a null value for an xsd:boolean the caller might get in throuble.
In .NET it’s not a problem to return a Boolean because it can’t be null. That’s because Boolean is a value type.
Whereas in Java boolean and Boolean are different types in .NET they are the same System::Boolean.
Java
boolean (native)
Boolean (java.lang.Boolean reference type)
C#
bool (System.Boolean value type)
Boolean (System.Boolean value type)