How can I get an element from linked list with given index in java?

Question

I'm learning about link-list in Java. and I'm want to write a method to give the value of node based on given index

I write a function, but it does not pass some of testcases, and I dont know why?. what is wrong with my logic?

//waypoint.java

public class Waypoint {
    int x  ;
    int y  ;
    public int getX()
    {
        return this.x;
    }
    public int getY()
    {
        return this.y;
    }
    public void setXY(int x, int y)
    {
        this.x = x;
        this.y = y;
    }

// TourElement.java

public class TourElement {
 private Waypoint points;
 private TourElement next;
  public void setWaypoint( Waypoint points)
 {
   this.points = points; 
 }
  public void setTourElement(TourElement next)
  {
      this.next = next;
  }
 Waypoint getWaypoint()
 {
     return this.points;
 }

 TourElement getNext()
 {
     return this.next;
 }

int getNoOfWaypoints()//  return the number of waypoints in the list
{
    int count = 1;
    TourElement current = getNext();
    while(current.next != null)
    {
        count++;
        current = current.next;
        System.out.println(count);
    }
    return count;
} 

// here is method I'm strucking with:

Waypoint getWaypointAt(int index)
{
   int totalElement = getNoOfWaypoints();
   int count = 0;
   TourElement current = getNext();
   if(index < totalElement && index >= 0)
   {
       while (current.next != null)
      {
        if(count == index)
          {
              return getWaypoint();
          }
         count++;
          current = current.next;
         }

       }
   return null;
}

//the testcase: //case 1: pass

public void test0GetWaypointAt_First() {
        TourElement elem = createElementList(new int[][] {{0, 0}, {1, 1}, {2, 2}});
        Waypoint expected = createWaypoint(0, 0);
        assertArrayEquals(expected.toArray(), elem.getWaypointAt(0).toArray());
    }

//case 2 and case 3: failed

public void test0GetWaypointAt_Snd() {
        TourElement elem = createElementList(new int[][] {{0, 0}, {1, 1}, {2, 2}});
        Waypoint expected = createWaypoint(1, 1);
        assertArrayEquals(expected.toArray(), elem.getWaypointAt(1).toArray());
    }

    @Test
    public void test0GetWaypointAt_Last() {
        TourElement elem = createElementList(new int[][] {{0, 0}, {1, 1}, {2, 2}});
        Waypoint expected = createWaypoint(2, 2);
        assertArrayEquals(expected.toArray(), elem.getWaypointAt(2).toArray());
    }

I dont know the reason. Please help me. Thank you so much in advance

Answer 1

Structure you've build with list seems ok, about your method getWaypointAt I see at least two problems:

First problem

   TourElement current = getNext();

getNext() is already the next element in your list, so you're skipping the first element all the time. It should be

   TourElement current = this;

Second problem

    return getWaypoint();

It returns waypoint from the head all the time. Should be

    return current.getWaypoint();

Seems like your first test should fail as well. I don't see the way you build elements in createElementList, it could be a reason why it pass.