Problem Adding incremented class member variable to arraylist inside loop

Trying to add an incremented class member variable 'nNodeIndex' to arraylist, but at the end of the loop all the values stored are identical to the last iteration increment??

Class with member variable:

import java.util.ArrayList;

public class Graph {

    private static ArrayList<GraphNode> Nodes = new ArrayList<GraphNode>();
    private static ArrayList<GraphEdge> Edges = new ArrayList<GraphEdge>();

    private static boolean diGraph;
    private static int nNodeIndex;

    private boolean uniqueEdge(int from, int to)
    {
        for(int i=0; i< Edges.size(); i++){
          if(Edges.get(i).from() == from && Edges.get(i).to() == to)
              return false;
        }
        return true;
    }

    private void removeInvalidEdges(int nodeIndex)
    {
        for(int i=0; i<Edges.size(); i++)
        {
            if(Edges.get(i).from() == nodeIndex)
                Edges.remove(i);
            if(Edges.get(i).to() == nodeIndex)
                Edges.remove(i);                    
        }
    }

    Graph(boolean directionalGraph)
    {
        diGraph     = directionalGraph;
        nNodeIndex  = 1;
    }

    public GraphNode getNode(int nodeIndex)
    {
        return Nodes.get(nodeIndex);
    }

    public int getIndexByVector(int x, int y)
    {
        for(int i=0; i<Nodes.size(); i++)
        {
            if(Nodes.get(i).x() == x && Nodes.get(i).y() == y)
                return i;
        }
        return -1;
    }

    public int nextFreeNodeIndex(){ return nNodeIndex; }

    public void addNode(GraphNode node)
    {
        if(Nodes.size() > 0)
            Nodes.add(node.index()-1, node);
        else
            Nodes.add(node);

        nNodeIndex++;  
    }

    public void removeNode(int index)
    {
        Nodes.get(index).setIndex(-1);

        removeInvalidEdges(index);
    }

    public void addEdge(GraphEdge edge)
    {
        if(uniqueEdge(edge.from(), edge.to()))
            Edges.add(edge);

        if(!diGraph)
        {
            if(uniqueEdge(edge.to(), edge.from()))
                Edges.add(new GraphEdge(edge.to(), edge.from()));
        }
    }

    public void removeEdge(GraphEdge edge)
    {
        for(int i=0; i<Edges.size(); i++)
            if(Edges.get(i).from() == edge.from() &&
               Edges.get(i).to() == edge.to())
            {
                Edges.remove(i);
            }
    }

    public int totalNodes(){ return Nodes.size(); }

    public int totalEdges(){ return Edges.size(); }

    public int nActiveNodes()
    {
        int count = 0;

        for(int i=0; i<Nodes.size(); i++)
        {
            if(Nodes.get(i).inde开发者_C百科x() != -1 )
                count++;
        }

        return count;
    }

    public void reset()
    {
        nNodeIndex = 1;
        Nodes.clear();
        Edges.clear();
    }

}

Use within main class:

  for(int row = 1; row <= boardWidth; row++){
       for(int col = 1; col <= boardHeight; col++){
          graph.addNode(new GraphNode(graph.nextFreeNodeIndex(), row, col));
       }
   }

Graph Node class:

public class GraphNode extends Square {

    private static int indexNum;

    GraphNode(int n, int x, int y)
    {
        super(x,y);
        indexNum = n;
    }

    public int index(){ return indexNum; }
    public void setIndex(int index){ indexNum = index; }
}

Do you need to show us the GraphNode class? I wonder if the node index held by it (set by the first parameter passed in its constructor) is a static variable.