Using enum type from JAR library in C

This article provides an introduction to cross-technology handling of enum type. In programming, an enum (short for enumeration) type is a special data type that enables for a variable to be a set of predefined constants. The variable must be equal to one of the values that have been predefined for it. Enums are used to create our own data types, just like classes. They are particularly useful when we want to represent a fixed set of constants, such as days of the week, states, colors, directions, and more. This makes the code more readable and less prone to errors.

Javonet allows you to reference and use modules or packages written in (Java/Kotlin/Groovy/Clojure, C#/VB.NET, Ruby, Perl, Python, JavaScript/TypeScript) like they were created in your technology. If have not yet created your first project check Javonet overview and quick start guides for your technology.

With Javonet, you can interact with enum types from JAR library as if they were available in C#, but interaction must be performed through the Javonet SDK API. This allows you to handle and manipulate enum values, pass them to methods, and return them from methods, all while maintaining the type safety and readability of your C# code.

Custom JAR library with enum type in C

With Javonet it is possible to reference any custom JAR library and interact with its methods declared on types defined within that module almost the same as with any other C# library.

Snippet below represents the sample code from JAR library which contains enum type.

public enum Fruit {
	Apple,
	Banana,
	Orange,
	Mango
}

public static ArrayList<Fruit> Fruits = new ArrayList<Fruit>();

public static String addFruitsToList(Fruit[] fruits) {
	Fruits.addAll(Arrays.asList(fruits));
	return String.format("%d fruits on the list", Fruits.size());
}

Javonet SDK contains various methods to interact with enums and consume the results in C#:

// use Activate only once in your app
Javonet.Activate("your-license-key");

// create called runtime context
var calledRuntime = Javonet.InMemory().Jvm();

// set up variables
string libraryPath = resourcesDirectory + "/TestClass.jar";

// load custom library
calledRuntime.LoadLibrary(libraryPath);

//get enum
var enumType = calledRuntime.GetType("TestClass$Fruit");

//create enum items
var fruit1 = calledRuntime.GetEnumItem(enumType, "Mango");
var fruit2 = calledRuntime.GetEnumItem(enumType, "Orange");

//get items' names and values
var fruit1Name = (string)fruit1.GetEnumName().Execute().GetValue();
var fruit2Name = (string)fruit2.GetEnumName().Execute().GetValue();
var fruit1Value = (int)fruit1.GetEnumValue().Execute().GetValue();
var fruit2Value = (int)fruit2.GetEnumValue().Execute().GetValue();


// write result to console
System.Console.WriteLine("{0}: {1}, {2}: {3}", fruit1Name, fruit1Value, fruit2Name, fruit2Value);

This snippet uses in memory runtime bridging to load the JAR library and next retrieves reference to specific enum type. Then two enum items are created. Their values and names are checked.

Enum items can be passed to JAR library method:

// use Activate only once in your app
Javonet.Activate("your-license-key");

// create called runtime context
var calledRuntime = Javonet.InMemory().Jvm();

// set up variables
string libraryPath = resourcesDirectory + "/TestClass.jar";
string className = "TestClass";

// load custom library
calledRuntime.LoadLibrary(libraryPath);

//get enum
var enumType = calledRuntime.GetType("TestClass$Fruit");

//create enum items
var apple = calledRuntime.GetEnumItem(enumType, "Apple");
var mango = calledRuntime.GetEnumItem(enumType, "Mango");

// create fruits array
InvocationContext[] fruitsList = { apple, mango };

// get type from the runtime
var calledRuntimeType = calledRuntime.GetType(className);

// invoke type's static method
var response = calledRuntimeType.
               InvokeStaticMethod("addFruitsToList", (object)fruitsList).
               Execute();

// get value from response
string result = (string)response.GetValue();

// write result to console
System.Console.WriteLine(result);

In this example, two enum items are created, too. Then array of enums is created and passed to method which adds enum items to list.

The same operation can be performed remotely by just changing the new Runtime Context invocation from in memory to tcp that will create and interact with your JAR library objects on any remote node, container or service that hosts Javonet Code Gateway. This way you can preserve the same logic in your application and instantly switch between monolithic and microservices architecture without the need to implement the integration layer based on web services or other remote invocation methods.

Read more about use cases and software architecture scenarios where Javonet runtime bridging technology can support your development process.