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What is a NullPointerException, and how do I fix it?（12个回答）
4天前关闭。
我尝试使用Optaplanner，并使用Optaplannerspring-boot-starter创建了一个简单的项目，以解决目前只有一个硬约束的简单VRP问题。
我的域模型非常简单，一个包含体积、重量容量的车辆类和包含体积和重量值的订单类。

@Getter
@Setter
@ToString
@PlanningEntity
public class Vehicle {

    @PlanningId
    private Long id;

    private int weightCapacity;
    private int volumeCapacity;
    private double guaranteeCheck;

    @PlanningListVariable(valueRangeProviderRefs = "orderRange")
    private List<Order> orders;

    public Vehicle() {
    }

    public Vehicle(long id, int volume, int weight) {
        this.id = id;
        this.volumeCapacity=volume;
        this.weightCapacity=weight;
    }

    public int getTotalVolumeCapacity() {
        int totalDemand = 0;
        for (Order order : orders) {
            totalDemand += order.getVolume();
        }
        return totalDemand;
    }

    public int getTotalWeightCapacity(){
        int totalDemand = 0;
        for (Order order : orders) {
            totalDemand += order.getWeight();
        }
        return totalDemand;
    }
}

@Getter
@Setter
@ToString
public class Order {
    private Long id;
    private String reference;
    private double weight;
    private double volume;
//    private double amount;
    private Location location;

    public Order() {
    }

    public Order(long id, int volume, int weight, Location location) {
        this.id = id;
        this.reference = this.id.toString();
        this.volume = volume;
        this.weight = weight;
        this.location = location;
    }
}

我创建了一个vrp解决方案类，如下所示：

@NoArgsConstructor
@AllArgsConstructor
@PlanningSolution
@Getter
@Setter
public class VehicleRoutingSolution {

    @ProblemFactCollectionProperty
    @ValueRangeProvider(id = "orderRange")
    private List<Order> orders;

    @ValueRangeProvider
    @PlanningEntityCollectionProperty
    private List<Vehicle> vehicles;

    @PlanningScore
    private HardSoftLongScore score;

    public VehicleRoutingSolution(List<Order> orders, List<Vehicle> vehicles) {
        this.orders = orders;
        this.vehicles = vehicles;
    }
}

这里的问题很简单，我试图根据一个硬约束为车辆分配订单，该硬约束基于quarkus quickstart官方示例制定如下：

public class VehicleRoutingConstraintProvider implements ConstraintProvider {
    @Override
    public Constraint[] defineConstraints(ConstraintFactory constraintFactory) {
        return new Constraint[]{
                // Hard constraints
                vehicleCapacity(constraintFactory),
                // Soft constraints
        };
    }


    protected Constraint vehicleCapacity(ConstraintFactory factory) {
        return factory.forEach(Vehicle.class)
                .filter(vehicle -> vehicle.getTotalVolumeCapacity() > vehicle.getVolumeCapacity())
                .penalizeLong(HardSoftLongScore.ONE_HARD,
                              vehicle -> vehicle.getTotalVolumeCapacity() - vehicle.getVolumeCapacity())
                .asConstraint("vehicleCapacity");
    }
}

当我启动求解程序在数据集上查找解决方案时，它显示以下问题：
Cannot invoke "java.util.List.size()" because the return value of "org.optaplanner.core.impl.domain.variable.descriptor.ListVariableDescriptor.getListVariable(Object)" is null
我在想，要么是我的一个解决方案变量没有正确初始化，要么是最新版本（自4月22日起可用）发生了变化。
求解器执行代码如下：

List<Order> orders = createOrdersDataSet();
        List<Vehicle> vehicles = createVehicleDataSet();

        UUID problemId = UUID.randomUUID();
        VehicleRoutingSolution problem = new VehicleRoutingSolution(orders, vehicles);
        // Submit the problem to start solving
        SolverJob<VehicleRoutingSolution, UUID> solverJob = solverManager.solve(problemId, problem);
        VehicleRoutingSolution solution;
        try {
            // Wait until the solving ends
            solution = solverJob.getFinalBestSolution();
        } catch (InterruptedException | ExecutionException e) {
            throw new IllegalStateException("Solving failed.", e);
        }

        log.info("Your best score is: {}", solution.getScore());