Graph Representation using Java ArrayList

Prerequisite : Graph and its representations

In this article, we will be discussing Adjacency List representation of Graph using ArrayList in Java.

Following is adjacency list representation of the above graph.

Adjacency List Representation of Graph



The idea is to use ArrayList of ArrayLists.

filter_none

edit
close

play_arrow

link
brightness_4
code

// Java code to demonstrate Graph representation
// using ArrayList in Java
import java.util.*;
  
class Test {
  
    static void addEdge(ArrayList<ArrayList<Integer> > adj,
                        int u, int v)
    {
        adj.get(u).add(v);
        adj.get(v).add(u);
    }
  
    static void printAdjacencyList(ArrayList<ArrayList<Integer> > adj)
    {
        for (int i = 0; i < adj.size(); i++) {
            System.out.println("Adjacency list of " + i);
            for (int j = 0; j < adj.get(i).size(); j++) {
                System.out.print(adj.get(i).get(j) + " ");
            }
            System.out.println();
        }
    }
  
    public static void main(String[] args)
    {
        // Creating a graph with 5 vertices
        int V = 5;
        ArrayList<ArrayList<Integer> > adj = new ArrayList<ArrayList<Integer> >(V);
        for (int i = 0; i < V; i++)
            adj.add(new ArrayList<Integer>());
  
        // Adding edges one by one.
        addEdge(adj, 0, 1);
        addEdge(adj, 0, 4);
        addEdge(adj, 1, 2);
        addEdge(adj, 1, 3);
        addEdge(adj, 1, 4);
        addEdge(adj, 2, 3);
        addEdge(adj, 3, 4);
        printAdjacencyList(adj);
    }
}

chevron_right


Output:

Adjacency list of 0
1 4 
Adjacency list of 1
0 2 3 4 
Adjacency list of 2
1 3 
Adjacency list of 3
1 2 4 
Adjacency list of 4
0 1 3

Similar Implementation using a separate Class for Graph.

filter_none

edit
close

play_arrow

link
brightness_4
code

// Java code to demonstrate Graph representation
// using ArrayList in Java
import java.util.*;
  
class Graph {
    ArrayList<ArrayList<Integer> > adj;
    int V;
    Graph(int v)
    {
        V = v;
        adj = new ArrayList<ArrayList<Integer> >(V);
        for (int i = 0; i < V; i++)
            adj.add(new ArrayList<Integer>());
    }
  
    void addEdge(int u, int v)
    {
        adj.get(u).add(v);
        adj.get(v).add(u);
    }
  
    void printAdjacencyList()
    {
        for (int i = 0; i < adj.size(); i++) {
            System.out.println("Adjacency list of " + i);
            for (int j = 0; j < adj.get(i).size(); j++) {
                System.out.print(adj.get(i).get(j) + " ");
            }
            System.out.println();
        }
    }
}
  
class Test {
  
    public static void main(String[] args)
    {
        // Creating a graph with 5 vertices
        int V = 5;
  
        Graph g = new Graph(V);
  
        // Adding edges one by one.
        g.addEdge(0, 1);
        g.addEdge(0, 4);
        g.addEdge(1, 2);
        g.addEdge(1, 3);
        g.addEdge(1, 4);
        g.addEdge(2, 3);
        g.addEdge(3, 4);
        g.printAdjacencyList();
    }
}

chevron_right


Output:

Adjacency list of 0
1 4 
Adjacency list of 1
0 2 3 4 
Adjacency list of 2
1 3 
Adjacency list of 3
1 2 4 
Adjacency list of 4
0 1 3


My Personal Notes arrow_drop_up

Check out this Author's contributed articles.

If you like GeeksforGeeks and would like to contribute, you can also write an article using contribute.geeksforgeeks.org or mail your article to contribute@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.

Please Improve this article if you find anything incorrect by clicking on the "Improve Article" button below.




Article Tags :
Practice Tags :


1


Please write to us at contribute@geeksforgeeks.org to report any issue with the above content.