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);
            
        }
}