UNO components are Java archive (JAR) files (Java components) or dynamic link libraries (C++ components), with the ability to instantiate objects which can integrate themselves into the UNO environment. For this purpose, components must contain certain static methods (Java) or export functions (C++) to be called by a UNO service manager. In the following, these methods are called component operations.
There must be a method to supply single-service factories for each object implemented in the component. Through this method, the service manager can get a single factory for a specific object and ask the factory to create the object contained in the component. Furthermore, there has to be a method which writes registration information about the component, which is used when a component is registered with the service manager. In C++, an additional function is necessary that informs the component loader about the compiler used to build the component.
The component operations are always necessary in components and they are language specific. Later, when Java and C++ are discussed, we will show how to write them.
The illustration shows a component which contains three implemented objects. Two of them, srv1 and srv2 implement a single service specification (Service1 and Service2), whereas srv3_4 supports two services at once (Service3 and Service4).
The objects implemented in a component must support a number of core UNO interfaces to be fully usable from all parts of the OpenOffice.org application. These core interfaces are discussed in the next section. The individual functionality of the objects is covered by the additional interfaces they export. Usually these interfaces are enclosed in a service specification.
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