Package org.jnetstream.lang.npl.type

NPL language data type definitions.

See:
Description

Interface Summary

DataOperations	Interface that defines various operations that can be performed on a particular data type.
DataType	Factory and compiler definitions for data types in NPL language.

Class Summary

AbstractDataType

Enum Summary

DataOperations.DataOperation

Package org.jnetstream.lang.npl.type Description

NPL language data type definitions. This package allows new data types to be added to NPL language. The default implementation supplies all the standard data types part of the core NPL language, but this package provides interfaces and classes which can be used to add new data type to NPL language.

Steps required to add a new data type

There are only 3 steps that are required in order to add a completely new data type to NPL.

1. Create a data type controller/factory.
2. Create or define which object to hold the data you would like to use
3. Register the data type controller defined in step 1 with the NplRuntime

Each data type within NPL consists of atleast 2 objects. The first object is a controller for the all instances of this particular data type. There is only a single controller object required. The controller object is allocated only once for the registry and then referenced by compiled NPL programs to perform certain work on various data types. The second object is allocated to hold actual data and this is also the object that the public API normally exposes. This data object does not have to implement any special interfaces. This object will be returned as the value from various getter methods of the compiled NPL definitions.

Example: adding a new data type

In this example we are going to add a new NPL data type that holds images. A packet containing GIF data in its payload can utilize our new data type to not only read the GIF data out of the packet, but can display it in some graphical window, outside the NPL scope of course.

Here is how we are going to setup our data type. Since java SE already contains a nice API to read images, we will use the imageio package as the basis for our new type. What we do need to do is create a ImageDataType class that extends the AbstractDataType that provides the basic implementation of all the DataType methods, this is the controller. The controller is the object that will create instances of variables and fields referenced in NPL definition, it will know how to read the data out of the packet's data buffer and initialize any new instances of the jpeg object we are going to use from the standard java SE.

[Under construction - MWB - March 2007]