Java Program to Check whether Undirected Graph is Connected using BFS

This Java program, to perform the bfs traversal of a given undirected graph in the form of the adjacency matrix and check for the connectivity of the graph.the bfs traversal makes use of a queue.

Here is the source code of the Java program to check the connectivity of the undirected graph using BFS. The Java program is successfully compiled and run on a Linux system. The program output is also shown below.

import java.util.InputMismatchException;
import java.util.LinkedList;
import java.util.Queue;
import java.util.Scanner;
 
public class UndirectedConnectivityBFS
{
    private Queue<Integer> queue;
 
    public UndirectedConnectivityBFS()
    {
        queue = new LinkedList<Integer>();
    }
 
    public void bfs(int adjacency_matrix[][], int source)
    {
        int number_of_nodes = adjacency_matrix.length - 1;
 
        int[] visited = new int[number_of_nodes + 1];
        int i, element;
        visited = 1;
        queue.add(source);
        while (!queue.isEmpty())
        {
            element = queue.remove();
            i = element;
            while (i <= number_of_nodes)
            {
                if (adjacency_matrix[element][i] == 1 && visited[i] == 0)
                {
                    queue.add(i);
                    visited[i] = 1;
                }
                i++;
            }
        }  
        boolean connected = false; 
 
        for (int vertex = 1; vertex <= number_of_nodes; vertex++)
        {
            if (visited[vertex] == 1)
            {
                connected = true;
            } else
            {
                connected = false;
                break;
            }
        }
 
        if (connected)
        {
            System.out.println("The graph is connected");
        } else
        {
            System.out.println("The graph is disconnected");
        }
    }
 
    public static void main(String... arg)
    {
        int number_no_nodes, source;
        Scanner scanner = null;
 
        try
        {
            System.out.println("Enter the number of nodes in the graph");
            scanner = new Scanner(System.in);
            number_no_nodes = scanner.nextInt();
 
            int adjacency_matrix[][] = new int[number_no_nodes + 1][number_no_nodes + 1];
            System.out.println("Enter the adjacency matrix");
            for (int i = 1; i <= number_no_nodes; i++)
                for (int j = 1; j <= number_no_nodes; j++)
                    adjacency_matrix[i][j] = scanner.nextInt();
 
            for (int i = 1; i <= number_of_nodes; i++)
            {
                for (int j = 1; j <= number_of_nodes; j++)
                {
                    if (adjacency_matrix[i][j] ==  1 && adjacency_matrix[j][i] == 0)
                    {
                        adjacency_matrix[j][i] = 1;
                    }
                }
            }
 
            System.out.println("Enter the source for the graph");
            source = scanner.nextInt();
 
            UndirectedConnectivityBFS undirectedConnectivity= new UndirectedConnectivityBFS();
            undirectedConnectivity.bfs(adjacency_matrix, source);
 
        } catch (InputMismatchException inputMismatch)
        {
            System.out.println("Wrong Input Format");
        }
        scanner.close();
    }
}

$javac UndirectedConnectivityBFS.java
$java UndirectedConnectivityBFS
Enter the number of nodes in the graph
5
Enter the adjacency matrix
0 1 1 1 0
0 0 1 0 0
0 0 0 0 0
0 0 0 0 0
0 0 0 0 0
Enter the source for the graph
1
The graph is disconnected