GraphBFS.java

import java.util.ArrayList;
import java.util.LinkedList;
import java.util.Queue;

public class GraphBFS {

    private Graph G;
    private boolean[] visited;

    private ArrayList<Integer> order = new ArrayList<>();

    public GraphBFS(Graph G){

        this.G = G;
        visited = new boolean[G.V()];
        for(int v = 0; v < G.V(); v ++)
            if(!visited[v])
                bfs(v);
    }

    private void bfs(int s){

        Queue<Integer> queue = new LinkedList<>();
        queue.add(s);
        visited[s] = true;
        while(!queue.isEmpty()){
            int v = queue.remove();
            order.add(v);

            for(int w: G.adj(v))
                if(!visited[w]){
                    queue.add(w);
                    visited[w] = true;
                }
        }
    }

    public Iterable<Integer> order(){
        return order;
    }

    public static void main(String[] args){

        Graph g = new Graph("g.txt");
        GraphBFS graphBFS = new GraphBFS(g);
        System.out.println("BFS Order : " + graphBFS.order());
    }
}