Working with n-D C++ arrays from JAR library

This article provides an introduction to cross-technology handling of multidimensional arrays. Data structures are one of the essential aspects of every piece of software. Any application constantly process various information, that very often require specific grouping and access strategies. This aspect is addressed by arrays and more advanced collection types. By using the Javonet framework, users gain ability to easily and effectively work with data structures originating from JAR library. Every array from JAR library is treated as reference.

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.
ith Javonet you can interact with arrays from JAR library like they were available in C++ but invocation must be performed through Javonet SDK API.

Custom JAR library with arrays handling

With Javonet it is possible to reference any custom JAR library and interact with arrays 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 that has methods which return or process the arrays:

public String[] get1DArray() {
	return new String[]{"one", "two", "three", "four", "five"};
}

public String[][] get2DArray() {
	return new String[][]{{"S00", "S01"},{"S10", "S11"}};
}

public double addArrayElementsAndMultiply(Double[] myArray, double myValue) {
	Double sum = 0.0;
	for (Double value : myArray) {
		sum += value;
	}
	return sum * myValue;
}

Javonet SDK contains various methods to interact with arrays and consume the results in C++:

Get element of C++ 2D array from JAR library

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

// create called runtime context
auto calledRuntime = Javonet::InMemory()->Jvm();

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

// load custom library
calledRuntime->LoadLibrary(libraryPath);

// get type from the runtime
auto calledRuntimeType = calledRuntime->GetType(className);

// create type's instance
auto instance = calledRuntimeType->CreateInstance();

// invoke instance's method
auto array = instance->InvokeInstanceMethod("get2DArray")->Execute();

// get index from array
auto response1 = array->GetIndex({ 1, 1 })->Execute();
std::vector<std::any> indexes = { 0, 0 };
auto response2 = array->GetIndex(indexes)->Execute();

// get value from response
auto result1 = std::any_cast<std::string>(response1->GetValue());
auto result2 = std::any_cast<std::string>(response2->GetValue());

// write result to console
std::cout << result1 << std::endl;
std::cout << result2 << std::endl;

In the snippet above, get2DArray method is used to get reference to 2D array from JAR library. Method getIndex is used to get element from the array. Depending on calling technology there is one or more ways to get element from array.

Set element of C++ 2D array from JAR library

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

// create called runtime context
auto calledRuntime = Javonet::InMemory()->Jvm();

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

// load custom library
calledRuntime->LoadLibrary(libraryPath);

// get type from the runtime
auto calledRuntimeType = calledRuntime->GetType(className);

// create type's instance
auto instance = calledRuntimeType->CreateInstance();

// invoke instance's method
auto array = instance->InvokeInstanceMethod("get2DArray")->Execute();

// set element in array
array->SetIndex(std::vector<std::any>{1, 1}, "new value")->Execute();

// get index from array
auto response = array->GetIndex({ 1, 1 })->Execute();

// get value from response
auto result = std::any_cast<std::string>(response->GetValue());

// write result to console
std::cout << result << std::endl;

In the snippet above, get2DArray method is used to get reference to 2D array from JAR library. Method setIndex is used to set element of the array.

Get size and rank of 2D array

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

// create called runtime context
auto calledRuntime = Javonet::InMemory()->Jvm();

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

// load custom library
calledRuntime->LoadLibrary(libraryPath);

// get type from the runtime
auto calledRuntimeType = calledRuntime->GetType(className)->Execute();

// create type's instance
auto instance = calledRuntimeType->CreateInstance()->Execute();

// invoke instance's method
auto array = instance->InvokeInstanceMethod("get2DArray")->Execute();

// three ways to get elements from array
auto response1 = array->GetSize()->Execute();
auto response2 = array->GetRank()->Execute();

// get value from response
auto result1 = std::any_cast<int>(response1->GetValue());
auto result2 = std::any_cast<int>(response2->GetValue());

// write result to console
std::cout << result1 << std::endl;
std::cout << result2 << std::endl;

In the snippet above, get2DArray method is used to get reference to 2D array from JAR library. Method getSize is used to get number of elements of the array.
Method getRank is used to get number of dimensions of the array.

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.

Additional references