I think you are using controlP5 am i right ?

If you wanna use a method on each slider object you have to :

• Use an array or an ArrayList to store your sliders and then loop for each slider object,

OR

• Call the setWindow method when you create a new Slider object.

Look at this example for the second solution (i'd use the first one which provide more flexibility).

1. import controlP5.*;
2. ControlP5 cP5;
3. 
   
4. void setup() {
5.   size(200, 200);
6.   cP5 = new ControlP5(this);
7.   for (int i = 0; i<8; i++) {
8.     // setValue can be replace by setWindow or any Slider's method
9.     ((Slider)cP5.addSlider("slider0" + i, 0, 1, 0, i*15, 40, 10)).setValue(random(1));
10.   }
11. }
12. 
    
13. void draw() {
14. }

I think you can use groups or some controlP5 to do this as well

I go for method 1.

Thanks