面向对象设计中概念与实例的区分：解决共享对象状态混乱问题

class Car {
    int volume; // 油量
    String model; // 型号

    public Car(int volume, String model) {
        this.volume = volume;
        this.model = model;
    }
}

class Person {
    String name;
    Car car; // 每个人都有一辆“车”

    public Person(String name, Car car) {
        this.name = name;
        this.car = car;
    }

    public void decreaseVolume() {
        if (this.car != null) {
            this.car.volume--;
        }
    }
}

Car car1 = new Car(100, "Ford100");
Person p1 = new Person("Alice", car1);
Person p2 = new Person("Bob", car1);

// Bob的车油量减少
p2.decreaseVolume();

// 1. 定义汽车型号/类别
class CarCategory {
    String brand;       // 品牌
    String model;       // 型号
    int maxVolume;      // 最大油箱容量

    public CarCategory(String brand, String model, int maxVolume) {
        this.brand = brand;
        this.model = model;
        this.maxVolume = maxVolume;
    }

    // Getter methods
    public String getBrand() { return brand; }
    public String getModel() { return model; }
    public int getMaxVolume() { return maxVolume; }
}

// 2. 定义具体的汽车实例
class Car {
    CarCategory category;   // 关联的汽车型号，强制在构造时指定
    String serialNumber;    // 序列号，唯一标识一辆车
    int currentVolume;      // 当前油量，这是实例的独立状态
    String color;           // 颜色
    Person owner;           // 车主

    public Car(CarCategory category, String serialNumber, String color, Person owner) {
        if (category == null) {
            throw new IllegalArgumentException("CarCategory cannot be null.");
        }
        this.category = category;
        this.serialNumber = serialNumber;
        this.currentVolume = category.getMaxVolume(); // 初始油量可以设置为最大容量
        this.color = color;
        this.owner = owner;
    }

    public void decreaseVolume(int amount) {
        if (currentVolume - amount >= 0) {
            this.currentVolume -= amount;
        } else {
            this.currentVolume = 0;
            System.out.println("Warning: Fuel tank is empty!");
        }
    }

    // Getter methods
    public CarCategory getCategory() { return category; }
    public String getSerialNumber() { return serialNumber; }
    public int getCurrentVolume() { return currentVolume; }
    public String getColor() { return color; }
    public Person getOwner() { return owner; }
    public void setOwner(Person owner) { this.owner = owner; }
}

// 3. Person类与具体的Car实例关联
class Person {
    String name;
    // 一个人可以有多辆车，使用集合存储
    // List<Car> cars; 
    // 或者如果一个人只有一辆主车
    Car primaryCar; 

    public Person(String name, Car primaryCar) {
        this.name = name;
        this.primaryCar = primaryCar;
        if (primaryCar != null) {
            primaryCar.setOwner(this); // 确保Car实例知道它的owner
        }
    }

    public void driveCar(int distance) {
        if (primaryCar != null) {
            int fuelConsumption = distance / 10; // 假设每10单位距离消耗1单位油量
            System.out.println(name + " is driving " + primaryCar.getCategory().getModel() + " (SN: " + primaryCar.getSerialNumber() + ") for " + distance + " units.");
            primaryCar.decreaseVolume(fuelConsumption);
            System.out.println("Remaining fuel for " + name + "'s car: " + primaryCar.getCurrentVolume());
        } else {
            System.out.println(name + " does not have a primary car to drive.");
        }
    }

    // Getter methods
    public String getName() { return name; }
    public Car getPrimaryCar() { return primaryCar; }
}

// 定义一个汽车型号
CarCategory fordFocusCategory = new CarCategory("Ford", "Focus", 50);

// 创建两辆具体的汽车实例，它们都属于"Ford Focus"型号
Car aliceCar = new Car(fordFocusCategory, "SN001", "Blue", null);
Car bobCar = new Car(fordFocusCategory, "SN002", "Red", null);

// 创建两个人，并将各自的汽车分配给他们
Person alice = new Person("Alice", aliceCar);
Person bob = new Person("Bob", bobCar);

// Alice开车，消耗油量
alice.driveCar(100); // Alice's car fuel: 40

// Bob开车，消耗油量
bob.driveCar(50);   // Bob's car fuel: 45

// 检查各自的油量
System.out.println("Alice's car current fuel: " + alice.getPrimaryCar().getCurrentVolume()); // Output: 40
System.out.println("Bob's car current fuel: " + bob.getPrimaryCar().getCurrentVolume());     // Output: 45