Use .NET Framework DLL enum type in Java app

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 .NET Framework DLL as if they were available in Java, 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 Java code.

Custom .NET Framework DLL with enum type

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

Snippet below represents the sample code from .NET Framework DLL which contains enum type.

namespace TestClass
{
	public class TestClass
	{
		public TestClass() { }

		public enum Fruit
		{
		    Apple,
		    Banana,
		    Orange,
		    Mango
		}
		
		public static System.Collections.Generic.List<Fruit> Fruits = new System.Collections.Generic.List<Fruit>();
		
		public static string AddFruitsToList(Fruit[] fruits)
		{
		    Fruits.AddRange(fruits);
		    return string.Format("{0} fruits on the list", Fruits.Count);
		}
	}
}
public enum Fruit
{
    Apple,
    Banana,
    Orange,
    Mango
}

public static System.Collections.Generic.List<Fruit> Fruits = new System.Collections.Generic.List<Fruit>();

public static string AddFruitsToList(Fruit[] fruits)
{
    Fruits.AddRange(fruits);
    return string.Format("{0} fruits on the list", Fruits.Count);
}

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

import com.javonet.sdk.*;

public class SampleProgram {

    private static final String resourcesDirectory = ".";
    public static void main(String []args) {

        // use activate only once in your app
        Javonet.activate("your-license-key");
        
        // create called runtime context
        RuntimeContext calledRuntime = Javonet.inMemory().clr();
        
        // set up variables
        String libraryPath = resourcesDirectory + "/TestClass.dll";
        
        // load custom library
        calledRuntime.loadLibrary(libraryPath);
        
        // get enum
        InvocationContext enumType = calledRuntime.getType("TestClass.TestClass+Fruit");
        
        // create enum's items
        InvocationContext fruit1 = calledRuntime.getEnumItem(enumType, "Mango");
        InvocationContext fruit2 = calledRuntime.getEnumItem(enumType, "Orange");
        
        //get items' names and values
        String fruit1Name = (String) fruit1.getEnumName().execute().getValue();
        String fruit2Name = (String) fruit2.getEnumName().execute().getValue();
        Integer fruit1Value = (Integer) fruit1.getEnumValue().execute().getValue();
        Integer fruit2Value = (Integer) fruit2.getEnumValue().execute().getValue();
        
        // write result to console
        System.out.println(fruit1Name + ": " + fruit1Value + ", " + fruit2Name + ": " + fruit2Value);
     }
}namespace TestClass
{
	public class TestClass
	{
		public TestClass() { }

		public enum Fruit
		{
		    Apple,
		    Banana,
		    Orange,
		    Mango
		}
		
		public static System.Collections.Generic.List<Fruit> Fruits = new System.Collections.Generic.List<Fruit>();
		
		public static string AddFruitsToList(Fruit[] fruits)
		{
		    Fruits.AddRange(fruits);
		    return string.Format("{0} fruits on the list", Fruits.Count);
		}
	}
}
// use activate only once in your app
Javonet.activate("your-license-key");

// create called runtime context
RuntimeContext calledRuntime = Javonet.inMemory().clr();

// set up variables
String libraryPath = resourcesDirectory + "/TestClass.dll";

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

// get enum
InvocationContext enumType = calledRuntime.getType("TestClass.TestClass+Fruit");

// create enum's items
InvocationContext fruit1 = calledRuntime.getEnumItem(enumType, "Mango");
InvocationContext fruit2 = calledRuntime.getEnumItem(enumType, "Orange");

//get items' names and values
String fruit1Name = (String) fruit1.getEnumName().execute().getValue();
String fruit2Name = (String) fruit2.getEnumName().execute().getValue();
Integer fruit1Value = (Integer) fruit1.getEnumValue().execute().getValue();
Integer fruit2Value = (Integer) fruit2.getEnumValue().execute().getValue();

// write result to console
System.out.println(fruit1Name + ": " + fruit1Value + ", " + fruit2Name + ": " + fruit2Value);

This snippet uses in memory runtime bridging to load the .NET Framework DLL 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 .NET Framework DLL method:

import com.javonet.sdk.*;

public class SampleProgram {

    private static final String resourcesDirectory = ".";
    public static void main(String []args) {

        // use activate only once in your app
        Javonet.activate("your-license-key");
        
        // create called runtime context
        RuntimeContext calledRuntime = Javonet.inMemory().clr();
        
        // set up variables
        String libraryPath = resourcesDirectory + "/TestClass.dll";
        String className = "TestClass.TestClass";
        
        // load custom library
        calledRuntime.loadLibrary(libraryPath);
        
        // get enum
        InvocationContext enumType = calledRuntime.getType("TestClass.TestClass+Fruit");
        
        // create enum's items
        InvocationContext apple = calledRuntime.getEnumItem(enumType, "Apple");
        InvocationContext mango = calledRuntime.getEnumItem(enumType, "Mango");
        
        // create fruits arrays
        InvocationContext[] fruits1ToAdd = new InvocationContext[] {apple, mango};
        
        // get type from runtime
        InvocationContext calledRuntimeType = calledRuntime.getType(className).execute();
        
        // invoke type's method
        InvocationContext response = calledRuntimeType.invokeStaticMethod("AddFruitsToList", (Object)fruits1ToAdd).execute();
        
        // get value from response
        String result = (String) response.getValue();
        
        // write result to console
        System.out.println(result);
     }
}namespace TestClass
{
	public class TestClass
	{
		public TestClass() { }

		public enum Fruit
		{
		    Apple,
		    Banana,
		    Orange,
		    Mango
		}
		
		public static System.Collections.Generic.List<Fruit> Fruits = new System.Collections.Generic.List<Fruit>();
		
		public static string AddFruitsToList(Fruit[] fruits)
		{
		    Fruits.AddRange(fruits);
		    return string.Format("{0} fruits on the list", Fruits.Count);
		}
	}
}
// use activate only once in your app
Javonet.activate("your-license-key");

// create called runtime context
RuntimeContext calledRuntime = Javonet.inMemory().clr();

// set up variables
String libraryPath = resourcesDirectory + "/TestClass.dll";
String className = "TestClass.TestClass";

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

// get enum
InvocationContext enumType = calledRuntime.getType("TestClass.TestClass+Fruit");

// create enum's items
InvocationContext apple = calledRuntime.getEnumItem(enumType, "Apple");
InvocationContext mango = calledRuntime.getEnumItem(enumType, "Mango");

// create fruits arrays
InvocationContext[] fruits1ToAdd = new InvocationContext[] {apple, mango};

// get type from runtime
InvocationContext calledRuntimeType = calledRuntime.getType(className).execute();

// invoke type's method
InvocationContext response = calledRuntimeType.invokeStaticMethod("AddFruitsToList", (Object)fruits1ToAdd).execute();

// get value from response
String result = (String) response.getValue();

// write result to console
System.out.println(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 .NET Framework DLL 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.