# Graph Representation using Java ArrayList

• Difficulty Level : Hard
• Last Updated : 16 Apr, 2019

Prerequisite : Graph and its representations

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Following is adjacency list representation of the above graph.

The idea is to use ArrayList of ArrayLists.

 `// Java code to demonstrate Graph representation``// using ArrayList in Java``import` `java.util.*;`` ` `class` `Test {`` ` `    ``static` `void` `addEdge(ArrayList > adj,``                        ``int` `u, ``int` `v)``    ``{``        ``adj.get(u).add(v);``        ``adj.get(v).add(u);``    ``}`` ` `    ``static` `void` `printAdjacencyList(ArrayList > 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 > adj = ``new` `ArrayList >(V);``        ``for` `(``int` `i = ``0``; i < V; i++)``            ``adj.add(``new` `ArrayList());`` ` `        ``// 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);``    ``}``}`
Output:
```Adjacency list of 0
1 4
0 2 3 4
1 3
1 2 4
0 1 3
```

Similar Implementation using a separate Class for Graph.

 `// Java code to demonstrate Graph representation``// using ArrayList in Java``import` `java.util.*;`` ` `class` `Graph {``    ``ArrayList > adj;``    ``int` `V;``    ``Graph(``int` `v)``    ``{``        ``V = v;``        ``adj = ``new` `ArrayList >(V);``        ``for` `(``int` `i = ``0``; i < V; i++)``            ``adj.add(``new` `ArrayList());``    ``}`` ` `    ``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();``    ``}``}`
Output:
```Adjacency list of 0
1 4
0 2 3 4