Working with n-D Java arrays from Python package

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 Python package. Every array from Python package 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 Python package like they were available in Java but invocation must be performed through Javonet SDK API.

Custom Python package with arrays handling

With Javonet it is possible to reference any custom Python package and interact with arrays declared on types defined within that module almost the same as with any other Java library.

Snippet below represents the sample code from Python package that has methods which return or process the arrays:

def get_1d_array(self):
	return ["one", "two", "three", "four", "five"]

def get_2d_array(self):
	return [["S00", "S01"], ["S10","S11"]]

def add_array_elements_and_multiply(self, my_array, my_value):
	return sum(my_array) * my_value

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

Get element of Java 2D array from Python package

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

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

// set up variables
// path to directory with .py files
String libraryPath = resourcesDirectory;
String className = "TestClass.TestClass";

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

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

// create type's instance
InvocationContext instance = calledRuntimeType.createInstance(0, 1).execute();

// invoke instance's method
InvocationContext array = instance.invokeInstanceMethod("get_2d_array").execute();

// two ways to get index from array
InvocationContext response1 = array.getIndex(1, 1).execute();
InvocationContext response2 = array.getIndex((Object) new Integer[]{0, 1}).execute();

// get value from response
String result1 = (String) response1.getValue();
String result2 = (String) response2.getValue();

// write result to console
System.out.println(result1);
System.out.println(result2);

In the snippet above, get2DArray method is used to get reference to 2D array from Python package. 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 Java 2D array from Python package

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

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

// set up variables
// path to directory with .py files
String libraryPath = resourcesDirectory;
String className = "TestClass.TestClass";

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

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

// create type's instance
InvocationContext instance = calledRuntimeType.createInstance(0, 1).execute();

// invoke instance's method
InvocationContext array = instance.invokeInstanceMethod("get_2d_array").execute();

// set index in array
array.setIndex(new Integer[]{0, 1}, "new value").execute();

// get index from array
InvocationContext response = array.getIndex(0, 1).execute();

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

// write result to console
System.out.println(result);

In the snippet above, get2DArray method is used to get reference to 2D array from Python package. 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
RuntimeContext calledRuntime = Javonet.inMemory().python();

// set up variables
// path to directory with .py files
String libraryPath = resourcesDirectory;
String className = "TestClass.TestClass";

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

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

// create type's instance
InvocationContext instance = calledRuntimeType.createInstance(0, 1).execute();

// invoke instance's method
InvocationContext array = instance.invokeInstanceMethod("get_2d_array").execute();


// get array's size
Integer size = (Integer) array.getSize().execute().getValue();

// get array's rank
Integer rank = (Integer) array.getRank().execute().getValue();

// write result to console
System.out.println("Size: " + size);
System.out.println("Rank: " + rank);

In the snippet above, get2DArray method is used to get reference to 2D array from Python package. 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 Python package 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