//to represent a nonempty list of ImageFile objects
public class ConsListImageFile implements IListImageFile{

  public ImageFile first;
  public IListImageFile rest;

  public ConsListImageFile(ImageFile first, IListImageFile rest){
    this.first=first;
    this.rest=rest;
  }

  //does this non-empty list contain that ImageFile   
  public boolean contains(ImageFile that){ 
    return this.first.sameImageFile(that) ||
    this.rest.contains(that); 
  } 
}