Java中跨类调用现有对象方法：参数传递的最佳实践

public class Car {
    private boolean engineOn;
    private double fuelLevel; // 油量，单位：升

    public Car(double initialFuel) {
        this.fuelLevel = initialFuel;
        this.engineOn = false; // 初始状态：引擎关闭
        System.out.println("Car created with " + String.format("%.2f", fuelLevel) + " liters of fuel.");
    }

    public void startEngine() {
        if (!engineOn && fuelLevel > 0) {
            engineOn = true;
            System.out.println("Engine started.");
        } else if (fuelLevel <= 0) {
            System.out.println("Cannot start engine: Out of fuel.");
        } else {
            System.out.println("Engine is already on.");
        }
    }

    public void stopEngine() {
        if (engineOn) {
            engineOn = false;
            System.out.println("Engine stopped.");
        } else {
            System.out.println("Engine is already off.");
        }
    }

    public void consumeFuel(double amount) {
        if (engineOn) { // 只有引擎开启时才能消耗燃油
            if (fuelLevel >= amount) {
                fuelLevel -= amount;
                System.out.println("Consumed " + String.format("%.2f", amount) + " liters of fuel. Remaining: " + String.format("%.2f", fuelLevel) + " liters.");
            } else {
                System.out.println("Not enough fuel to consume " + String.format("%.2f", amount) + " liters. Remaining: " + String.format("%.2f", fuelLevel) + " liters.");
                // 燃油耗尽，自动关闭引擎
                if (fuelLevel <= 0) {
                    stopEngine();
                }
            }
        } else {
            System.out.println("Engine is off. Cannot consume fuel.");
        }
    }

    public double getFuelLevel() {
        return fuelLevel;
    }

    public boolean isEngineOn() {
        return engineOn;
    }
}

public class FuelConsumptionService {

    /**
     * 根据汽车状态和持续时间计算并消耗燃油。
     *
     * @param car           需要进行油耗模拟的Car对象实例。
     * @param isMoving      汽车是否正在行驶。
     * @param durationMinutes 模拟的持续时间，单位：分钟。
     */
    public void calculateAndConsumeFuel(Car car, boolean isMoving, double durationMinutes) {
        if (car == null) {
            System.out.println("Error: Car object is null. Cannot calculate fuel consumption.");
            return;
        }

        if (!car.isEngineOn()) {
            System.out.println("Engine is off. No fuel consumption will occur.");
            return;
        }

        double ratePerMinute; // 每分钟油耗率
        if (isMoving) {
            ratePerMinute = 6.0; // 行驶状态下每分钟消耗6升
            System.out.println("Car is moving. Simulating moving fuel consumption...");
        } else {
            ratePerMinute = 0.8; // 引擎开启怠速状态下每分钟消耗0.8升
            System.out.println("Engine is on (idle). Simulating idle fuel consumption...");
        }

        double totalConsumption = ratePerMinute * durationMinutes;
        car.consumeFuel(totalConsumption); // 调用传入Car对象的consumeFuel方法
    }
}

public class Main {
    public static void main(String[] args) {
        // 1. 创建一个Car对象实例，初始油量50升
        Car myCar = new Car(50.0);
        System.out.println("Current fuel level: " + String.format("%.2f", myCar.getFuelLevel()) + " liters.");

        // 2. 创建FuelConsumptionService对象实例
        FuelConsumptionService fuelService = new FuelConsumptionService();

        // 3. 启动引擎
        myCar.startEngine();

        // 4. 场景1：怠速油耗模拟
        System.out.println("\n--- Scenario 1: Idle Consumption (5 minutes) ---");
        fuelService.calculateAndConsumeFuel(myCar, false, 5); // 模拟怠速5分钟
        System.out.println("Fuel level after idle: " + String.format("%.2f", myCar.getFuelLevel()) + " liters.");

        // 5. 场景2：行驶油耗模拟
        System.out.println("\n--- Scenario 2: Moving Consumption (10 minutes) ---");
        fuelService.calculateAndConsumeFuel(myCar, true, 10); // 模拟行驶10分钟
        System.out.println("Fuel level after moving: " + String.format("%.2f", myCar.getFuelLevel()) + " liters.");

        // 6. 停止引擎
        myCar.stopEngine();

        // 7. 场景3：引擎关闭，无油耗
        System.out.println("\n--- Scenario 3: Engine Off (2 minutes) ---");
        fuelService.calculateAndConsumeFuel(myCar, false, 2); // 引擎关闭，不应消耗燃油
        System.out.println("Fuel level with engine off: " + String.format("%.2f", myCar.getFuelLevel()) + " liters.");

        // 8. 场景4：油量不足的情况
        System.out.println("\n--- Scenario 4: Low Fuel Test ---");
        Car lowFuelCar = new Car(0.5); // 只有0.5升油
        lowFuelCar.startEngine(); // 尝试启动引擎
        fuelService.calculateAndConsumeFuel(lowFuelCar, false, 1); // 模拟怠速1分钟，油量不足
        System.out.println("Fuel level of lowFuelCar: " + String.format("%.2f", lowFuelCar.getFuelLevel()) + " liters.");
        lowFuelCar.startEngine(); // 再次尝试启动，此时引擎可能已关闭
    }
}