NUHMAN.com

✅ Directed Graph in Java

💡 Characteristics:

• Edges have direction.
• If there's an edge from A → B, it's not implied that B → A exists.

🔧 Implementation

java

import java.util.*;

public class DirectedGraph {
    private Map<Integer, List<Integer>> adjList = new HashMap<>();

    public void addVertex(int vertex) {
        adjList.putIfAbsent(vertex, new ArrayList<>());
    }

    public void addEdge(int from, int to) {
        adjList.putIfAbsent(from, new ArrayList<>());
        adjList.putIfAbsent(to, new ArrayList<>());
        adjList.get(from).add(to); // One-way edge
    }

    public void printGraph() {
        for (var entry : adjList.entrySet()) {
            System.out.print("Vertex " + entry.getKey() + " → ");
            System.out.println(entry.getValue());
        }
    }

    public static void main(String[] args) {
        DirectedGraph graph = new DirectedGraph();
        graph.addVertex(1);
        graph.addVertex(2);
        graph.addVertex(3);

        graph.addEdge(1, 2);
        graph.addEdge(2, 3);
        graph.addEdge(1, 3);

        graph.printGraph();
    }
}

✅ Undirected Graph in Java

💡 Characteristics:

• Edges are bidirectional.
• If A is connected to B, then B is also connected to A.

🔧 Implementation

java

import java.util.*;

public class UndirectedGraph {
    private Map<Integer, List<Integer>> adjList = new HashMap<>();

    public void addVertex(int vertex) {
        adjList.putIfAbsent(vertex, new ArrayList<>());
    }

    public void addEdge(int v1, int v2) {
        adjList.putIfAbsent(v1, new ArrayList<>());
        adjList.putIfAbsent(v2, new ArrayList<>());

        adjList.get(v1).add(v2);
        adjList.get(v2).add(v1); // Reverse edge for undirected connection
    }

    public void printGraph() {
        for (var entry : adjList.entrySet()) {
            System.out.print("Vertex " + entry.getKey() + " ↔ ");
            System.out.println(entry.getValue());
        }
    }

    public static void main(String[] args) {
        UndirectedGraph graph = new UndirectedGraph();
        graph.addVertex(1);
        graph.addVertex(2);
        graph.addVertex(3);

        graph.addEdge(1, 2);
        graph.addEdge(2, 3);
        graph.addEdge(1, 3);

        graph.printGraph();
    }
}

🔁 Summary Table

FeatureDirected GraphUndirected GraphEdge DirectionOne-way (A → B)Two-way (A ↔ B)addEdge BehaviorAdds edge from from → to onlyAdds both v1 → v2 and v2 → v1Use CasesWeb Crawlers, Dependency GraphsSocial Networks, Road Maps