i am new to JAVA. I think all my code is corect. I dont actually know what is wrong with my code but it shows error.
Error:
Exception in thread "main" java.lang.NullPointerException: Cannot invoke "F28DA_CW2.FlightsReader.getAirports()" because "this.flightReader" is null
at F28DA_CW2.FlyingPlanner.leastCost(FlyingPlanner.java:206)
at F28DA_CW2.FlyingPlannerMainPartBC.main(FlyingPlannerMainPartBC.java:29)
Below is the code i am working on:
Main file
import java.io.FileNotFoundException;
public class FlyingPlannerMainPartBC {
public static void main(String[] args) throws FlyingPlannerException, FileNotFoundException {
FlyingPlanner fi;
fi = new FlyingPlanner();
try {
fi.populate(new FlightsReader());
// Implement here your user interface using the methods of Part B. You could
// optionally expand it to use the methods of Part C.
} catch (FileNotFoundException | FlyingPlannerException e) {
e.printStackTrace();
}
FlightsReader flightReader = new FlightsReader();
flightReader.getAirports();
flightReader.getFlights();
FlyingPlanner pr = new FlyingPlanner();
System.out.println(pr.leastCost("EDI", "DXB")); // line: 29
}
}
a snippet of the error source.
@Override
public Journey leastCost(String from, String to) throws FlyingPlannerException {
// TODO Auto-generated method stub
HashSet<String[]> airports = flightReader.getAirports(); //line206
HashSet<String[]> flights = flightReader.getFlights();
DefaultDirectedWeightedGraph<String, DefaultWeightedEdge> leastCost = new DefaultDirectedWeightedGraph<>(
DefaultWeightedEdge.class);
for (String[] flight : flights) {
leastCost.addVertex(flight[1]);
leastCost.addVertex(flight[3]);
leastCost.addEdge(flight[1], flight[3]);
leastCost.setEdgeWeight(flight[1], flight[3], Integer.parseInt(flight[5]));
}
DijkstraShortestPath<String, DefaultWeightedEdge> dijkstraAlg = new DijkstraShortestPath<>(leastCost);
GraphPath<String, DefaultWeightedEdge> shortestPath = dijkstraAlg.getPath(from, to);
int totalCost = 0;
int totalHop = 0;
int totalTime = 0;
for (DefaultWeightedEdge defaultWeightedEdge : shortestPath.getEdgeList()) {
totalCost = totalCost + (int) leastCost.getEdgeWeight(defaultWeightedEdge);
totalHop = totalHop + 1;
String v1 = leastCost.getEdgeSource(defaultWeightedEdge);
String v2 = leastCost.getEdgeTarget(defaultWeightedEdge);
System.out.println(totalHop + ". " + v1 + "--->" + v2);
}
Journey journey = new Journey();
journey.setTotalCost(totalCost);
journey.setTotalHop(totalHop);
System.out.println(totalCost);
System.out.println(totalHop);
return journey;
}
Last the Scanner file that reads the file (where i think is completely fine)
import java.io.File;
import java.io.FileNotFoundException;
import java.util.HashSet;
import java.util.Scanner;
public class FlightsReader {
private static final File flightsDatasetFolder = new File("FlightsDataset");
private static final File flightsDatasetFlights = new File(flightsDatasetFolder, "flights.csv");
private static final File flightsDatasetAirports = new File(flightsDatasetFolder, "airports.csv");
private HashSet<String[]> airports;
private HashSet<String[]> flights;
public FlightsReader() throws FileNotFoundException, FlyingPlannerException {
this.airports = new HashSet<String[]>();
this.flights = new HashSet<String[]>();
// Adding flights, and building list of needed airport
HashSet<String> airportsNeeded = new HashSet<String>();
Scanner flightsScanner = new Scanner(flightsDatasetFlights);
while (flightsScanner.hasNextLine()) {
String line = flightsScanner.nextLine();
String[] fields = line.split(",");
String from = fields[1];
String to = fields[3];
airportsNeeded.add(from);
airportsNeeded.add(to);
this.flights.add(fields);
}
flightsScanner.close();
// Adding airports
Scanner airportsScanner = new Scanner(flightsDatasetAirports);
while (airportsScanner.hasNextLine()) {
String line = airportsScanner.nextLine();
String[] fields = line.split(",");
if (airportsNeeded.contains(fields[0])) {
this.airports.add(fields);
}
}
airportsScanner.close();
}
/**
* Returns a hash set of airport details (0: airport code, 1: city, 2: airport
* name)
*/
public HashSet<String[]> getAirports() {
return this.airports;
}
/**
* Returns a hash set of flight details (0: flight code, 1: airport code of
* departure, 2: departure time GMT, 3: airport code of arrival, 4: arrival time
* GMT, 5: flight cost)
*/
public HashSet<String[]> getFlights() {
return this.flights;
}
}
I think the flight reader codes works well. I not really sure what the problem is.
Thank you to any kind JAVA master out there that could help me.
