Reference implementation of a "collection" where elements are accessible by a positional offset.

Path.java

public class Path {
    private List<Element> elements = new ArrayList<>();
    
    public class Element {
        public double lenght;
    }
    
    public void addElement(Element element) {
        elements.add(element);
    }
    
    public Element getElementAtOffset(double offset) {
        double pos = 0;
        for (Element element: elements) {
            pos += element.lenght;
            if (pos >= offset)
                return element;
        }
        return null;
    }
}