Java/W3/Car/Car.java

public class Car {
    private final String licensePlate; // 车牌号（不可变）
    private String brand;              // 品牌
    private String model;              // 型号
    private double dailyRent;         // 日租金
    private boolean isRented;          // 是否已租出

    // 静态变量：统计车辆总数
    private static int totalCars = 0;

    // 全参构造方法
    public Car(String licensePlate, String brand, String model, double dailyRent) {
        this.licensePlate = licensePlate;
        this.brand = brand;
        this.model = model;
        setDailyRent(dailyRent); // 通过setter赋值，自动校验
        this.isRented = false;   // 初始状态为未租出
        totalCars++;             // 每创建一个对象，总数+1
    }

    // 三参构造方法（日租金默认300）
    public Car(String licensePlate, String brand, String model) {
        this(licensePlate, brand, model, 300.0);
    }

    // Getter/Setter
    public String getLicensePlate() {
        return licensePlate;
    }

    public String getBrand() {
        return brand;
    }

    public void setBrand(String brand) {
        this.brand = brand;
    }

    public String getModel() {
        return model;
    }

    public void setModel(String model) {
        this.model = model;
    }

    public double getDailyRent() {
        return dailyRent;
    }

    public void setDailyRent(double dailyRent) {
        if (dailyRent > 0) {
            this.dailyRent = dailyRent;
        } else {
            System.out.println("日租金必须大于0，设置失败！");
        }
    }

    public boolean isRented() {
        return isRented;
    }

    // 业务方法：租车
    public void rentCar() {
        if (isRented) {
            System.out.println("车辆已租出，无法再次租出！");
        } else {
            isRented = true;
            System.out.println("车辆租出成功！");
        }
    }

    // 业务方法：还车
    public void returnCar() {
        if (!isRented) {
            System.out.println("车辆未被租用，无需归还！");
        } else {
            isRented = false;
            System.out.println("车辆归还成功！");
        }
    }

    // 业务方法：计算租金
    public double calculateRent(int days) {
        return dailyRent * days;
    }

    // 静态方法：获取车辆总数
    public static int getTotalCars() {
        return totalCars;
    }

    // 打印车辆信息
    public void displayInfo() {
        System.out.println("车牌号：" + licensePlate +
                "，品牌：" + brand +
                "，型号：" + model +
                "，日租金：" + dailyRent +
                "元/天，状态：" + (isRented ? "已租出" : "可租"));
    }
}