public class LinkedL {
    private int numberOfElements = 0;
    private Element firstObj;

    LinkedL(Element firstObj){
        this.firstObj = firstObj;
    }

    public void addToBeginning(Element obj){
        obj.setNextEl(firstObj);
        firstObj = obj;
        numberOfElements++;
    }

    public void addToEnding(Element obj){
        Element obj2 = firstObj;
        Element obj1 = obj2;
        while (obj1.getNextEl() != null){
            obj1 = obj2.getNextEl();
            obj2 = obj1;
        }
        obj1.setNextEl(obj);
        numberOfElements++;
    }

    public void addToMiddle(Element obj){
        int counter = 1;
        Element obj2 = firstObj;
        Element obj1 = obj2;
        if (numberOfElements > 1) {
            while (counter != numberOfElements / 2) {
                obj1 = obj2.getNextEl();
                obj2 = obj1;
                counter++;
            }
        }
        obj.setNextEl(obj1.getNextEl());
        obj1.setNextEl(obj);
    }

    public void deleteFirst(){
        Element obj;
        obj = firstObj.getNextEl();
        firstObj = obj;
    }

    public void deleteMiddle(){
        Element next = firstObj;
        Element previous = next;
        int counter = 1;
        if (numberOfElements > 1) {
            while (counter != numberOfElements / 2) {
                previous = next.getNextEl();
                next = previous;
                counter++;
            }
            next = previous.getNextEl();
            previous.setNextEl(next.getNextEl());
        }
    }

    public void deleteLast(){
        Element obj2 = firstObj;
        Element obj1 = obj2;
        Element previous = obj2;
        while (obj1.getNextEl() != null){
            obj1 = obj2.getNextEl();
            previous = obj2;
            obj2 = obj1;
        }
        previous.setNextEl(null);
    }

    public void firstElementChanging(Element obj){
        obj.setNextEl(firstObj.getNextEl());
        firstObj = obj;
    }

    public void middleElementChanging(Element obj){
        Element obj2 = firstObj;
        Element obj1 = obj2;
        int counter = 1;

        if (numberOfElements > 1) {
            while (counter != numberOfElements / 2) {
                obj1 = obj2.getNextEl();
                counter++;
                obj2 = obj1;
            }
            obj2 = obj1.getNextEl();
            obj.setNextEl(obj2.getNextEl());
            obj1.setNextEl(obj);
        }
    }

    public void lastElementChanging(Element obj){
        Element obj2 = firstObj;
        Element obj1 = obj2;
        Element previous = obj2;
        while (obj1.getNextEl() != null){
            previous = obj2;
            obj1 = obj2.getNextEl();
            obj2 = obj1;
        }
        previous.setNextEl(null);
    }

    public int sum(){
        int result = firstObj.getData();
        Element obj2 = firstObj;
        Element obj1 = obj2;
        while (obj1.getNextEl() != null){
            obj1 = obj2.getNextEl();
            result = result + obj1.getData();
            obj2 = obj1;
        }
        return result;
    }

    public int index(int data){
        Element obj2 = firstObj;
        Element obj1 = obj2;
        int counter = 0;
        while (obj1.getData() != data){
            obj1 = obj2.getNextEl();
            obj2 = obj1;
            counter++;
        }
        return counter;
    }

    public int getElement(int index){
        Element obj2 = firstObj;
        Element obj1 = obj2;
        int counter = 0;
        while (counter != index){
            obj1 = obj2.getNextEl();
            obj2 = obj1;
            counter++;
        }
        return obj1.getData();
    }
}