完成したプログラムだと思っていたところにたどり着きましたが、今ではjavaがこれを引っ張っています。
私が得るエラーは次のとおりです。
Exception in thread "main" java.lang.NullPointerException
at hirecardemo.HireCar.isAvailable(HireCar.java:68)
at hirecardemo.HireCarDemo.runSimulation(HireCarDemo.java:49)
at hirecardemo.HireCarDemo.main(HireCarDemo.java:25)
Java Result: 1
メインクラス：
package hirecardemo;
import java.util.Random;
public class HireCarDemo {
public static void main(String[] args) {
HireCar car0 = new HireCar("Toyota", "AV77 FGJ", 6000, 12300, 41500);
HireCar car1 = new HireCar("Mercedes", "DI99 FTZ", 6700, 7000, 91800);
HireCar car2 = new HireCar("Toyota", "FG82 FTP", 25000, 12000, 72000);
HireCar car3 = new HireCar("Vauxhall", "TW56 LTS", 10000, 11000, 19001);
HireCar car4 = new HireCar("Ford", "TD85 LTU", 13000, 12300, 12000);
HireCar car5 = new HireCar("Susuki", "GU12 UTJ", 12000, 10000, 50000);
HireCar[] fleet = {car0, car1, car2, car3, car4, car5};
int minMileage = 1000;
int maxMileage = 60000;
int numberOFevents = 12;
String [] results = HireCarDemo.runSimulation(fleet, numberOFevents,
minMileage, maxMileage);
for(int i = 0; i < numberOFevents; i++) {
System.out.println(results[i]);
}
}
/**
* @param fleet the fleet of hire cars
* @param numberOFevents the size of the events table to be generated
* @param minMileage the assumed minimum mileage driven by any hired
* car
* @param maxMileage the assumed maximum mileage driven by any hired
* car
* @return table of events generated during the simulation
*/
public static String[] runSimulation(HireCar [] fleet, int numberOFevents,
int minMileage, int maxMileage) {
int n = fleet.length; // Number of cars in the fleet.
Random carGenerator = new Random();
String [] events = new String [numberOFevents];
for(int i = 0; i < numberOFevents; i++) {
int randomNumber = carGenerator.nextInt(n-1);
if(fleet[randomNumber].isAvailable() == true)
{
fleet[randomNumber].hireOut();
events[i] = fleet[randomNumber].getRegNumber() + " <HIRE OUT>";
}
else if(fleet[randomNumber].isOnHire() == true)
{
Random mileage = new Random();
int randomMileage = mileage.nextInt(maxMileage - minMileage);
if(fleet[randomNumber].isBeingServiced() == true)
{
events[i] = fleet[randomNumber].getRegNumber() +
" <RETURN FROM HIRE>" + " <SEND FOR SERVICE>";
} else {
events[i] = fleet[randomNumber].getRegNumber() +
" <RETURN FROM HIRE>";
}
}
else
{
fleet[randomNumber].makeAvailable();
events[i] = fleet[randomNumber].getRegNumber() +
" <RETURN FROM SERVICE>";
}
}
return events;
}
}
これに伴う私の別のクラスは次のとおりです。
//******************************************************************************
// HireCar.java Author: Ryan Holder
//
// Represents the car hire company's fleet of cars and the information on them.
//******************************************************************************
package hirecardemo;
public class HireCar {
private String manufacturer, regNumber, carStatus;
private int mileage, serviceInterval, lastService; // All in miles.
private boolean serviceDue() {
if((mileage- lastService) >= serviceInterval) {
this.sendForService();
return true;
} else {
return false;
}
}
private void sendForService() {
carStatus = "Servicing";
}
//--------------------------------------------------------------------------
// Default Constructor: Sets information for a new car.
//--------------------------------------------------------------------------
public HireCar(String demoManufacturer, String demoRegNumber) {
manufacturer = demoManufacturer;
regNumber = demoRegNumber;
carStatus = "Available";
serviceInterval = 0;
lastService = 0;
mileage = 0;
}
public HireCar(String demoManufacturer, String demoRegNumber,
int demoMileage, int demoServiceInterval, int lastInterval) {
manufacturer = demoManufacturer;
regNumber = demoRegNumber;
mileage = demoMileage;
}
public void setMileage(int demoMileage) {
mileage = demoMileage;
}
public void setServiceInterval(int demoServiceInterval) {
serviceInterval = demoServiceInterval;
}
public void setLastService(int demoLastService) {
lastService = demoLastService;
}
public String getRegNumber() {
return regNumber;
}
public void makeAvailable() {
carStatus = "Available";
}
public boolean isAvailable() {
if(carStatus.equals("Available") || carStatus.equals("Return from Service")) {
return true;
} else {
return false;
}
}
public boolean isOnHire() {
if(carStatus.equals("On Hire")) {
return true;
} else {
return false;
}
}
public boolean isBeingServiced() {
if(carStatus.equals("Being Serviced")) {
return true;
} else {
return false;
}
}
public void hireOut() {
carStatus = "On Hire";
}
public void returnFromHire() {
if(this.serviceDue() == true) {
carStatus = "Being Serviced";
} else {
carStatus = "Available For Hire";
}
}
public void returnFromService() {
carStatus = "Return From Service";
}
public String ToString() {
return("Manufacturer: <" + this.manufacturer + ">/n "
+ "Registration Number: <" + this.regNumber + ">/n"
+ "Mileage: <" + this.mileage + ">/n"
+ "Service Interval: <" + this.serviceInterval + "</n"
+ "Last Service: <" + this.lastService + "</n"
+ "Status: <" + this.carStatus + "</n");
}
}