I was tring to use that method addGarbage to add an object from the class Garbage to a Garbage linked list.

void addGarbage(List<Garbage> list){
  Garbage garbage = new Garbage();
  list.add(garbage);
}

addGarbage(GarbageList); 

the add method works when using other types, and the GarbageList was declared as a List of the type Garbage.

Here’s its declaration:

List<Garbage> GarbageList = new List<>();

And here is the add method (that works):

void add(T data) {
    Node<T> newNode = new Node<T>(data);
    if (head == null) {
      head = newNode;
    } else {
      Node end = head;
      while (end.next != null) {
        end = end.next;
      }
      end.next = newNode;
    }
  }