Thread: help with using Java ArrayList

I'm learning to build an directed graph data structure using adjacency lists, so I thought I'd use LinkedLists to ensure efficient linked list used and I wanted to use an array of Linked list, but I had trouble so I decided to use ArrayList of LinkedList of type Integer, but compiler complains about generics.

The problem I have is having a wrapper that adds a new vertex to the current end of a LL (so it's a wrapper for addLast(Elem e) which is really a LinkedList method)

import java.util.*;
import java.lang.*;
 
class Graph//implemented via adjacency lists
{
	public Graph(int size)
	{
		this.size = size;
		l = new LinkedList(size);
	}
 
	public void add_to_end(Integer i)//problem here...
	{
		this.l.add(i);//PROBLEM: this.l is a Linked List data member but compiler complains...
	}
 
 
	public void print(){return;}//prints each index (so each adjacent node for a given node)
 
 
	public void dft(){return;}//Depth-first traversal of current graph
 
 
	public void bft(){return;}//breadth-first " "
 
 
	public int get_size(){return this.size;}
 
	private int size;//number of vertices
	private ArrayList l;
}
 
public class Graphs_runner
{	
	public static void main(String[] args)
	{
	}
}