A graph is a data structure that consists of a set of vertices (also known as nodes) and a set of edges that connect these vertices. Each edge represents a relationship or connection between two vertices. Graphs can be directed, where the edges have a specific direction, or undirected, where the edges have no direction. Graphs are commonly used in computer science to model complex systems, such as social networks, transportation networks, and computer networks. They are also used in algorithms for tasks such as shortest path finding, network flow optimization, and clustering. Keep reading below to learn how to use a Graph in Java.

Looking to get a head start on your next software interview? Pickup a copy of the best book to prepare: Cracking The Coding Interview!

Buy Now On Amazon

How to use a Graph in Java with example code

Java is a popular programming language used for developing a wide range of applications. One of the most common tasks in Java programming is working with graphs. In this blog post, we will discuss how to use a graph in Java with example code.

A graph is a collection of nodes (also known as vertices) and edges that connect these nodes. Graphs are used to represent complex relationships between objects or entities. In Java, graphs can be implemented using various data structures such as arrays, linked lists, and hash tables.

To use a graph in Java, you first need to define the data structure that will hold the nodes and edges. One common way to do this is by using an adjacency list. An adjacency list is a collection of linked lists, where each linked list represents the edges connected to a particular node.

Here is an example code snippet that demonstrates how to create an adjacency list in Java:

import java.util.*;

public class Graph {
private int V;
private LinkedList[] adjList;

public Graph(int V) {
this.V = V;
adjList = new LinkedList[V];
for (int i = 0; i < V; i++) { adjList[i] = new LinkedList<>();

public void addEdge(int src, int dest) {

public void printGraph() {
for (int i = 0; i < V; i++) { System.out.print(i + ": "); for (int j : adjList[i]) { System.out.print(j + " "); } System.out.println(); } } }

In this example, we define a class called Graph that has an array of linked lists to represent the adjacency list. The addEdge() method is used to add edges to the graph, and the printGraph() method is used to print the graph.

To use this graph, you can create an instance of the Graph class and add edges to it using the addEdge() method. Here is an example code snippet that demonstrates how to use the Graph class:

public static void main(String[] args) {
Graph graph = new Graph(5);
graph.addEdge(0, 1);
graph.addEdge(0, 4);
graph.addEdge(1, 2);
graph.addEdge(1, 3);
graph.addEdge(1, 4);
graph.addEdge(2, 3);
graph.addEdge(3, 4);


In this example, we create a graph with 5 nodes and add edges between them using the addEdge() method. We then print the graph using the printGraph() method.

In conclusion, using a graph in Java is a common task that can be accomplished using various data structures such as adjacency lists. By following the example code provided in this blog post, you can easily create and use graphs in your Java programs.

What is a Graph in Java?

In conclusion, a graph in Java is a powerful data structure that allows us to represent complex relationships between objects. It is a collection of vertices or nodes that are connected by edges, which can be directed or undirected. Graphs can be used to solve a wide range of problems, from finding the shortest path between two points to modeling social networks and transportation systems. Java provides a variety of libraries and frameworks for working with graphs, including the Java Collections Framework and popular third-party libraries like JGraphT and GraphStream. By understanding the basics of graphs in Java, developers can build more efficient and effective applications that can handle complex data structures and relationships.

Elevate your software skills

Contact Us