Matlab Builder JA is a tool that allows you to compile Matlab functions into a Java Archive (JAR) file, which can be used in Java applications. However, Matlab Builder JA is a commercial product and is not available for free.

There is a free alternative to Matlab Builder JA called MATLAB Compiler SDK, which also allows you to compile Matlab functions into Java classes and JAR files. However, the SDK has some limitations compared to the full Matlab Builder JA product, such as a smaller set of supported Matlab functions and a lack of some deployment options.

To use Matlab Compiler SDK, you need a Matlab license and a license for the Compiler SDK itself. You can obtain a trial license for the SDK from MathWorks, the company behind Matlab. After the trial period, you need to purchase a license to continue using the SDK.

Alternatively, you can consider using other free and open-source tools that allow you to integrate Matlab with Java, such as the Matlab Control Toolbox for Java or JMatLink. These tools provide a different set of features compared to Matlab Builder JA and Matlab Compiler SDK, but may be sufficient for some use cases.