Simplest graph implementation in Java (30 lines)

This class Graph implements simplified Graph ADT without removals It can be used to practise in writing Depth first search (DFT) and Breadth first search (BFT)

List of nodes (vertices) have to be passed in constructor, but edges can be added later.

Only for educational purposes! :)

Usage

Create an instance

String[] nodes = {"A", "B", "C"};
List<String> nodesList = Arrays.asList(nodes);
Graph<String> graph = new Graph<>(nodesList);

Add edges

graph.addNeighbor("A", "B");
graph.addNeighbor("A", "C");
graph.addNeighbor("C", "A");

Do whatever you want

//print all nodes
for(Node<String> n: graph.getNodes()){
    System.out.println(n.element);
}

//print number of vertices that are adjacent to A
System.out.println(graph.getNode("A").neighbors.size());

//mark node as visited
graph.getNode("A").visited = true;

//maybe something like this
dfs(graph.getNodes().get(0));