java中类的定义和使用 类的声明和实例化全过程

public class Car {
    // 属性
    private String brand;
    private String model;
    private int year;

    // 构造函数
    public Car(String brand, String model, int year) {
        this.brand = brand;
        this.model = model;
        this.year = year;
    }

    // 方法
    public void startEngine() {
        System.out.println("Starting the engine of " + this.brand + " " + this.model);
    }

    // getter 和 setter 方法
    public String getBrand() {
        return brand;
    }

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

    // 其他getter和setter方法省略...
}

Car myCar = new Car("Tesla", "Model S", 2022);

myCar.startEngine(); // 输出: Starting the engine of Tesla Model S
System.out.println(myCar.getBrand()); // 输出: Tesla

public class ElectricCar extends Car {
    private double batteryCapacity;

    public ElectricCar(String brand, String model, int year, double batteryCapacity) {
        super(brand, model, year);
        this.batteryCapacity = batteryCapacity;
    }

    public void charge() {
        System.out.println("Charging " + this.getBrand() + " " + this.getModel());
    }

    public double getBatteryCapacity() {
        return batteryCapacity;
    }
}

ElectricCar myElectricCar = new ElectricCar("Tesla", "Model 3", 2022, 75.0);
myElectricCar.charge(); // 输出: Charging Tesla Model 3
System.out.println(myElectricCar.getBatteryCapacity()); // 输出: 75.0