This is show how the Java Monad is composed of.

mondads simple.java

import java.util.ArrayList;
import java.util.List;
import java.util.function.Function;

interface Functor<T, F extends Functor<?,?>> {
    <R> F map (Function<T, R> f);
}
class FList<T> implements Functor<T, FList<?>> {

    private final List<T> list;
    FList(List<T> value){
        this.list = List.copyOf(value);
    }
    @Override
    public <R> FList<?> map(Function<T, R> f) {
        var result = new ArrayList<R>(this.list.size());
        for (T t: list){
            result.add(f.apply(t));
        }
        return new FList<>(result);
    }


}