Cannot reference from static content

Question

Ok, so I was working on wrapping the main program and the classes together and I come up with that error...TopSort.java:40: non-static method addVertex(java.lang.String) cannot be referenced from a static context. I know why I am getting the error, I am just not sure what to do about it. When I first wrote the main, I was literally adding in the newVertexs, doing it like this...
Graph theGraph = new Graph();
theGraph.addVertex("A"); // 0
theGraph.addVertex("B"); // 1
and that all worked great. Now I am adding in the text file and have to read the data from the file so I am doing it like this
String toke1 = toke.nextToken();
if (toke1.equals("vertex"))
     newVertex = toke.nextToken();
     Graph.addVertex(newVertex);
but it throws the nonstatic error. How on earth do I go about modifying the class/main in order to circumvent that error?
Main -
[import java.io.*;
import java.util.*;
public class TopSort
public static void main (String args[])
     File sourceFile = new File(args[0]); // access the file
        if (sourceFile.exists() == false)                                          
          System.err.println("Oops: " + sourceFile + ": No such file");
          System.exit(1);
        System.out.println(args[0] + " is the name of the file you chose");
        Graph theGraph = new Graph();
        String newVertex, startEdge, endEdge;
        try //open the file, read the file into a string and then into the list
             FileReader fr = new FileReader(sourceFile);
             BufferedReader br = new BufferedReader(fr);
          String input;
          while ((input = br.readLine()) != null)
             StringTokenizer toke = new StringTokenizer(input);
             while (toke.hasMoreTokens())
                       String toke1 = toke.nextToken();
                       if (toke1.equals("vertex"))
                       newVertex = toke.nextToken();
                       Graph.addVertex(newVertex);
                       else if (toke1.equals("edge"))
                       startEdge = toke.nextToken();
                       endEdge = toke.nextToken();
                       System.out.println(startEdge + endEdge);
               }//close inner while
          }//close outer while
          br.close();
     }//close try
     catch (IOException e)
        System.out.println("Whoops, there's a mistake somewhere.");
}Class
class Vertex
   public String label;        // label (e.g. 'A')
   public Vertex(String newVertex)   // constructor
      { label = newVertex; }
   }  // end class Vertex
class Graph
   private final int MAX_VERTS = 20;
   private Vertex vertexList[]; // list of vertices
   private int adjMat[][];      // adjacency matrix
   private int nVerts;          // current number of vertices
   private String sortedArray[];
   public Graph()               // constructor
      vertexList = new Vertex[MAX_VERTS];
                                          // adjacency matrix
      adjMat = new int[MAX_VERTS][MAX_VERTS];
      nVerts = 0;
      for(int j=0; j<MAX_VERTS; j++)      // set adjacency
         for(int k=0; k<MAX_VERTS; k++)   //    matrix to 0
            adjMat[j][k] = 0;
      sortedArray = new String[MAX_VERTS];  // sorted vert labels
      }  // end constructor
   public void addVertex(String newVertex)
      vertexList[nVerts++] = new Vertex(newVertex);
   public void addEdge(int start, int end)
      adjMat[start][end] = 1;
   public void displayVertex(int v)
      System.out.print(vertexList[v].label);
   public void topo()  // toplogical sort
      int orig_nVerts = nVerts;  // remember how many verts
      while(nVerts > 0)  // while vertices remain,
         // get a vertex with no successors, or -1
         int currentVertex = noSuccessors();
         if(currentVertex == -1)       // must be a cycle
            System.out.println("ERROR: Graph has cycles");
            return;
         // insert vertex label in sorted array (start at end)
         sortedArray[nVerts-1] = vertexList[currentVertex].label;
         deleteVertex(currentVertex);  // delete vertex
         }  // end while
      // vertices all gone; display sortedArray
      System.out.print("Topologically sorted order: \n ");
      for(int j=0; j<orig_nVerts; j++)
         System.out.print( sortedArray[j]);
      System.out.println("");
      }  // end topo
   public int noSuccessors()  // returns vert with no successors
      {                       // (or -1 if no such verts)
      boolean isEdge;  // edge from row to column in adjMat
      for(int row=0; row<nVerts; row++)  // for each vertex,
         isEdge = false;                 // check edges
         for(int col=0; col<nVerts; col++)
            if( adjMat[row][col] > 0 )   // if edge to
               {                         // another,
               isEdge = true;
               break;                    // this vertex
               }                         //    has a successor
            }                            //    try another
         if( !isEdge )                   // if no edges,
            return row;                  //    has no successors
      return -1;                         // no such vertex
      }  // end noSuccessors()
   public void deleteVertex(int delVert)
      if(delVert != nVerts-1)      // if not last vertex,
         {                         // delete from vertexList
         for(int j=delVert; j<nVerts-1; j++)
            vertexList[j] = vertexList[j+1];
                                   // delete row from adjMat
         for(int row=delVert; row<nVerts-1; row++)
            moveRowUp(row, nVerts);
                                   // delete col from adjMat
         for(int col=delVert; col<nVerts-1; col++)
            moveColLeft(col, nVerts-1);
      nVerts--;                    // one less vertex
      }  // end deleteVertex
   private void moveRowUp(int row, int length)
      for(int col=0; col<length; col++)
         adjMat[row][col] = adjMat[row+1][col];
   private void moveColLeft(int col, int length)
      for(int row=0; row<length; row++)
         adjMat[row][col] = adjMat[row][col+1];
   }  // end class Graph
////////////////////////////////////////////////////////////////

Answer 1

I don't think I quite understand what you mean by
that, would you elucidate? Sorry, serious brain
fry...Sure; your addVertex() method isn't declared static. This means that you cannot call it as a class method, which was what you were doing when you wrote "Graph.addVertex()". Class members (as defined by the keyword static) refer to methods and variables that pertain to the overall class as a whole, as opposed to instance members that pertain to individual (instantiated) objects of that class.
For example, look at the java.lang.Integer class. It has static methods like parseInt() and instance methods like intValue(). The instance method (intValue()) requires that you have instantiated an Integer object from which to get the value. You can't just call Integer.intValue(), because there's no value for the overall Integer class!
Likewise, it doesn't make sense to require you to have an actual Integer object to parse a String to an int value. An actual Integer object wouldn't have anything to do with the process. Thus the parseInt() method is static, meaning you can call Integer.parseInt() to get the value of an int from a String.
Hope this helps!
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