Download jar file or use maven. psjava requires Java 1.6 (or above)
<dependency>
<groupId>org.psjava</groupId>
<artifactId>psjava</artifactId>
<version>0.1.19</version>
</dependency>// Let's construct a graph.
MutableDirectedWeightedGraph<String, Integer> graph = MutableDirectedWeightedGraph.create();
graph.insertVertex("A");
graph.insertVertex("B");
graph.insertVertex("C");
graph.addEdge("A", "C", 10);
graph.addEdge("A", "B", 15);
graph.addEdge("B", "C", -10); // negative weight is allowed in Johnson's algorithm
graph.addEdge("C", "A", 5);
// Let's get the shortest paths of all pairs.
// Johnson's algorithm is a combination of Bellman Ford's and Dijkstra's algorithm.
AllPairShortestPath johnson = GoodJohnsonAlgorithm.getInstance();
AllPairShortestPathResult<String, Integer, DirectedWeightedEdge<String, Integer>> res = johnson.calc(graph, IntegerNumberSystem.getInstance());
int distanceAToB = res.getDistance("A", "B"); // must be 15
int distanceBToC = res.getDistance("B", "A"); // must be -5
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