New to Java

I have been messing with ArrayList for awhile and today well working on this zombie game I'm making for class I got an error that I have never seen before and do not understand why I get this here is the code:

import java.util.ArrayList;

public class Room
{
    private String description;
    public HashMap<String, Room> exits;
    public static Room currentRoom;
    public ArrayList<Room> roomList = new ArrayList();
    
    public Room(String description) 
    {
        this.description = description;
        exits = new HashMap<String, Room>();
        roomList.add(this);
    }
    
    public void placeRandomZombies()
    {
        int listSize = roomList.size;
    }

And the error:

size has private access in java.util.ArrayList

Your help is much greatful