Implementing three functions at once into another evolution optimizer

Ive installed the Differential Evolution (DE) optimizer according to the instructions at https://github.com/skarjoko/differential-evolution/blob/master/Main.java and just running the code in eclipse works great and easily allows me to optimize the function examples.

Now to my problem: in the default mode, DE only performs singular function optimizations (e.g. f (x1) = y1), throwing away only the value of one function.

The model I need to optimize consists of three functions (e.g. f (x1) = y1, f (x2) = y2, f (x3) = y3)) and I need one value for each function separately. How do I get started implementing these three functions in DE?

Background information about the model: The model I have to optimize consists of three possible fractions of people who may or may not accept the behavior (the proportion of people who have just learned about the innovation, the proportion of people who intend to innovate, and the proportion of people who already use innovation). The diffusion of acceptance is modeled on a temporal and spatial discrete basis based on an agent.

Thank you in advance for your help!