Please see the spec.: http://download.oracle.com/otndocs/jcp/7224-javabeans-1.01-fr-spec-oth-JSpec/

For indexed properties the accessor type signatures are:
  void setter(int index, PropertyType value);  // indexed setter
  PropertyType getter(int index); // indexed getter
  void setter(PropertyType values[]); // array setter
  PropertyType[] getter(); // array getter


Consider an example:

import java.beans.*;
import java.util.Arrays;

public class Test {

    public static class C {

        private double x[] = new double[]{};

        @BeanProperty(description = "TEST_INDEXED", hidden = true, expert = false)
        public double getX(int i) throws IndexOutOfBoundsException {
            if (i >0 && i < x.length) { return x[i]; }
            else { throw new IndexOutOfBoundsException(); }
        }
        public void setX(int i, double v) throws IndexOutOfBoundsException {
            if (i >0 && i < x.length) { x[i] = v; }
            else { throw new IndexOutOfBoundsException(); }
        }
        
        @BeanProperty(description = "TEST", hidden = false, expert = true)
        public double[] getX() { return x; }
        public void setX(double a[]) { x = Arrays.copyOf(a, a.length); }
    }
    

    public static void main(String[] args) throws Exception {

        BeanInfo i = Introspector.getBeanInfo(C.class, Object.class);
        PropertyDescriptor pd[] = i.getPropertyDescriptors();
        
        for (PropertyDescriptor d: pd) {
            System.out.println(d.getShortDescription());
            System.out.println("hidden = " + d.isHidden());
            System.out.println("expert = " + d.isExpert());
            System.out.println("");
        }
    }
}


Output (Win 7, JDK9 b72):

TEST
hidden = true
expert = true

so,
1. the "hidden" value is seemingly invalid
2. how is it decided which property info should be used? could the info be somehow stored for both the alternatives?