install "MATLAB Compiler" & "MATLAB Compiler SDK" from : MATLAB -> APPS -> Get More Apps (Search that keywords in the add-on manager and install)
open MATLAB -> APPS -> Library Compiler
Add all your functions(.m files) from EXPORTED DUNCTIONS section
Optional : create samples for your functions from samples tab, it will generate sample java code for you
Pick "Java Package" from TYPE section
Submit Package Button
In the generated directory, there is an another directory named "for_redistribution_files_only", add this folder to your java appliction as library
Add MATLAB_PATH/R2020b(version)/toolbox/javabuilder/jar/javabuilder.jar to your java application as library