Connected components code

import java.util.List;
import java.util.ArrayList;

class ConnectedComponents {
    private boolean[] visited; // visited[v] = true if v connected to s
    private int[] id; // id[v] = id of component containing v
    private int count;
    
    /** find connected components in G  */
    public ConnectedComponents(Graph G) {
        // initialize data structures
        this.visited = new boolean[G.V()];
        this.id = new int[G.V()];
        this.count = 0; // number of components
        
        // run DFS from one vertex in each component
        for(int v = 0; v < G.V(); v++) {
            if(!visited[v]) {
                dfs(G, v);
                count++;   
            }
        }
    }
    
    /** are v and w connected? */
    boolean connected(int v, int w) {
        return id[v] == id[w];
    }
    
    /** number of connected components */
    int count() {
        return count;
    }
    
    /** component identifier for v */
    int id(int v) {
        return id[v];
    }
    
    private void dfs(Graph G, int v) {
        // all vertices discovered in same call of dfs have same id
        visited[v] = true;
        id[v] = count;
        for (int w : G.adj(v)) {
            if(!visited[w]) {
                dfs(G, w);
            }
        }
    }
    
    private static Graph prepareGraph() {
        int[][] edges = new int[][] {
            // {13, 13} V & E
            {0, 5},
            {4, 3},
            {0, 1},
            {9, 12},
            {6, 4},
            {5, 4},
            {0, 2},
            {11, 12},
            {9, 10},
            {0, 6},
            {7, 8},
            {9, 11},
            {5, 3}
		};
		
		Graph G = new Graph(13, 13);
		// add all edges 
		for(int i = 0; i < edges.length; i++) {
		    int v = edges[i][0];
		    int w = edges[i][1];
		    G.addEdge(v, w);
		}
		return G;
    }
    
    static class Graph {
        private final int V; // number of vertices
        private final int E; // number of edges
        private final List[] adj; // adjacency lists... 0 to V-1
        
        /** create an empty graph with V vertices */
        public Graph(int V, int E) {
            this.V = V;
            this.E = E;
            this.adj = new ArrayList[V]; // create empty graph with V vertices
            for(int i = 0; i < V; i++) {
                adj[i] = new ArrayList<>();
            }
        }
        
        /** add an edge v-w */
        public void addEdge(int v, int w) {
            // add edge v-w (parallel edges and self-loops allowed)
            adj[v].add(w);
            adj[w].add(v);
        }
        
        /** vertices adjacent to v */
        public Iterable adj(int v) {
            return adj[v];
        }
        
        /** number of vertices */
        public int V() {
            return V;
        }
        
        /** number of edges */
        public int E() {
            return E;
        }
    }
    
    public static void main (String[] args) {
	    System.out.println("Test connected components ");
		ConnectedComponents cc = new ConnectedComponents(prepareGraph());
		System.out.println("Number of connected components: " + cc.count());
		System.out.println("Id of 3 = " + cc.id(3));
		System.out.println("Id of 8 = " + cc.id(8));
		System.out.println("Id of 11 = " + cc.id(11));
		System.out.println("Is 0 & 3 connected? " + cc.connected(0, 3));
		System.out.println("Is 7 & 8 connected? " + cc.connected(7, 8));
		System.out.println("Is 10 & 11 connected? " + cc.connected(10, 11));
		System.out.println("Is 0 & 8 connected? " + cc.connected(0, 8));
		System.out.println("Is 7 & 3 connected? " + cc.connected(7, 3));
		System.out.println("Is 10 & 7 connected? " + cc.connected(10, 7));
	}
}

Output
Test connected components 
Number of connected components: 3
Id of 3 = 0
Id of 8 = 1
Id of 11 = 2
Is 0 & 3 connected? true
Is 7 & 8 connected? true
Is 10 & 11 connected? true
Is 0 & 8 connected? false
Is 7 & 3 connected? false
Is 10 & 7 connected? false