topological sort

A topological sort
of a dag G  is a linear ordering of all its vertices such that if G contains an
edge(u,v) then u appears before in the ordering. (If the graph contains a cycle,
then no linear ordering is possible.)

 package element_graph;

 import java.util.LinkedList;

 public class deapth_first_search {
     public static int time = 0;
     private static class vertex{
         private LinkedList<vertex> link;
         private String name;
         private String color;
         private vertex p;
         private int d,f;
         public vertex(String na,LinkedList<vertex> lin){
             name = na;
             link = lin;
             color = "white";
             p = null;
             d = 0;   //discover time
             f = 0;
         }
     }
     public static void DFS(vertex v){
         if(v.color == "white"){
             time = time + 1;
             v.d = time;   //discover time
             v.color = "gray";
             for (vertex u : v.link) {
                 if(u.color == "white"){
                     u.p = v;
                     DFS(u);
                 }
             }
             v.color = "black";
             time = time +1;
             v.f = time;
             System.out.println(v.name+v.f);
         }
     }
     public static void printpath(vertex s,vertex v){
         if(v == s){
             System.out.println(s.name);
         }
         else if(v.p == null){  //will not get s
             System.out.println("no way");
         }
         else{
             printpath(s,v.p);
             System.out.println(v.name+v.f);
         }
     }
      public static void main(String[] args) {
             LinkedList<vertex> sl = new LinkedList<vertex>();

             LinkedList<vertex> rl = new LinkedList<vertex>();

             LinkedList<vertex> vl = new LinkedList<vertex>();

             LinkedList<vertex> wl = new LinkedList<vertex>();

             LinkedList<vertex> tl = new LinkedList<vertex>();

             LinkedList<vertex> xl = new LinkedList<vertex>();

             LinkedList<vertex> ul = new LinkedList<vertex>();

             LinkedList<vertex> yl = new LinkedList<vertex>();

             vertex sv = new vertex("s",sl);
             vertex rv = new vertex("r",rl);
             vertex vv = new vertex("v",vl);
             vertex wv = new vertex("w",wl);
             vertex tv = new vertex("t",tl);
             vertex xv = new vertex("x",xl);
             vertex uv = new vertex("u",ul);
             vertex yv = new vertex("y",yl);
             sl.add(rv);
             sl.add(wv);
             //rl.add(sv);
             rl.add(vv);
             vl.add(rv);
             wl.add(xv);
             wl.add(tv);
             //wl.add(sv);
             tl.add(xv);
             tl.add(uv);
             //tl.add(wv);
             //xl.add(tv);
             xl.add(uv);
             xl.add(yv);
             //xl.add(wv);
             //xl.add(tv);
             //xl.add(xv);
             //xl.add(yv);
             //xl.add(uv);
             //xl.add(xv);
              DFS(sv);
             // printpath(sv,tv);

         }
 }