MatrixGraphs.java

public class MatrixGraphs {

	public static void main(String args[]) {
		AdjacencyMatrixGraph graph = new AdjacencyMatrixGraph(10);
		graph.addEdge(1, 2);
		graph.addEdge(1, 5);
		graph.addEdge(2, 5);
		graph.addEdge(1, 2);
		graph.addEdge(2, 3);
		graph.addEdge(3, 4);
		graph.addEdge(4, 1);
		graph.addEdge(2, 3);
		System.out.println(graph);
	}

}

class AdjacencyMatrixGraph {
	private int _numberOfVertices;
	private int _numberOfEdges;
	private int[][] _adjacency;

	static final int EDGE_EXIST = 1;
	static final int EDGE_NONE = 0;

	public AdjacencyMatrixGraph(int givenNumberOfVertices) {
		this.setNumberOfVertices(givenNumberOfVertices);
		this.setNumberOfEdges(0);
		this.setAdjacency(new int[givenNumberOfVertices][givenNumberOfVertices]);
		for (int i = 0; i < givenNumberOfVertices; i++) {
			for (int j = 0; j < givenNumberOfVertices; j++) {
				this.adjacency()[i][j] = AdjacencyMatrixGraph.EDGE_NONE;
			}
		}
	}

	private void setNumberOfVertices(int newNumberOfVertices) {
		this._numberOfVertices = newNumberOfVertices;
	}

	public int numberOfVertices() {
		return this._numberOfVertices;
	}

	private void setNumberOfEdges(int newNumberOfEdges) {
		this._numberOfEdges = newNumberOfEdges;
	}

	public int numberOfEdges() {
		return this._numberOfEdges;
	}

	private void setAdjacency(int[][] newAdjacency) {
		this._adjacency = newAdjacency;
	}

	private int[][] adjacency() {
		return this._adjacency;
	}

	private boolean adjacencyOfEdgeDoesExist(int from, int to) {
		return (this.adjacency()[from][to] != AdjacencyMatrixGraph.EDGE_NONE);
	}

	public boolean vertexDoesExist(int aVertex) {
		if (aVertex >= 0 && aVertex < this.numberOfVertices()) {
			return true;
		} else {
			return false;
		}
	}

	public boolean edgeDoesExist(int from, int to) {
		if (this.vertexDoesExist(from) && this.vertexDoesExist(to)) {
			return (this.adjacencyOfEdgeDoesExist(from, to));
		}

		return false;
	}

	/**
     * This method adds an edge to the graph between two specified
     * vertices 
     *
     * @param from the data of the vertex the edge is from
     * @param to the data of the vertex the edge is going to
     * @return returns true if the edge did not exist, return false if it already did
     */
	public boolean addEdge(int from, int to) {
		if (this.vertexDoesExist(from) && this.vertexDoesExist(to)) {
			if (!this.adjacencyOfEdgeDoesExist(from, to)) {
				this.adjacency()[from][to] = AdjacencyMatrixGraph.EDGE_EXIST;
				this.adjacency()[to][from] = AdjacencyMatrixGraph.EDGE_EXIST;
				this.setNumberOfEdges(this.numberOfEdges() + 1);
				return true;
			}
		}

		return false;
	}

	 /**
     * this method removes an edge from the graph between two specified
     * vertices 
     *
     * @param from the data of the vertex the edge is from
     * @param to the data of the vertex the edge is going to
     * @return returns false if the edge doesn't exist, returns true if the edge exists and is removed
     */
	public boolean removeEdge(int from, int to) {
		if(!this.vertexDoesExist(from) || !this.vertexDoesExist(to)) {
			if (this.adjacencyOfEdgeDoesExist(from, to)) {
				this.adjacency()[from][to] = AdjacencyMatrixGraph.EDGE_NONE;
				this.adjacency()[to][from] = AdjacencyMatrixGraph.EDGE_NONE;
				this.setNumberOfEdges(this.numberOfEdges() - 1);
				return true;
			}
		}
		return false;
	}

    /**
     * this gives a list of vertices in the graph and their adjacencies
     * 
     * @return returns a string describing this graph
     */
	public String toString() {
		String s = new String();
		s = "    ";
		for (int i = 0; i < this.numberOfVertices(); i++) {
			s = s + String.valueOf(i) + " ";
		}
		s = s + " \n";

		for (int i = 0; i < this.numberOfVertices(); i++) {
			s = s + String.valueOf(i) + " : ";
			for (int j = 0; j < this.numberOfVertices(); j++) {
				s = s + String.valueOf(this._adjacency[i][j]) + " ";
			}
			s = s + "\n";
		}
		return s;
	}

}