Java 继承 - 可以简化将父类(super class)对象传递到子类的过程吗？

Question

我们知道

String s = new Object();

会导致错误:

incompatible types: Object cannot be converted to String

因此，从下面的例子来看，我们不能这样做:

Car car = new Vehicle();

但是 Java 有这样的东西会有什么问题:

父类(super class):

    public class Vehicle {
        String color;
        int numberOfWheels;
        int maxSpeed;
        // etc.
    }

子类:

    public class Car extends Vehicle {

        String engineType;
        String transmissionType;
        int numberOfDoors;
        // etc.

        Car(Vehicle vehicle) {
                            // the theoretical idea of passing
                            // the superclass object within a subclass
            super = vehicle;
        }
    }

'super = vehicle;'将允许我们传递先前设置的父类(super class)(车辆)的所有值 一次到新的子类(汽车)。 用法是:

    public class App {

        public static void main(String[] args) {

            Vehicle vehicle = new Vehicle();
            vehicle.color = "GREEN";
            vehicle.maxSpeed = 100;
            vehicle.numberOfWheels = 4;

            Car car = new Car(vehicle);

                                        // this would print: GREEN
            System.out.println("Car color is: " + car.color);
        }
    }

也许已经有一种类似的简单方法。

“启蒙那些还在黑暗中的人……”

Answer 1

您可以做类似的事情，但您仍然需要提供 Car 特定信息(作为 Car 构造函数的参数，或默认值，或两者的结合)。

一种相当常见的方法是在 Vehicle 中为 Vehicle 定义一个复制构造函数:

public Vehicle(Vehicle other) {
    this.color = other.color;
    this.numberOfWheels = other.numberOfWheels;
    this.maxSpeed = other.maxSpeed;
}

然后在 Car 中，您使用该复制构造函数，然后充实 Car 详细信息:

public Car(Vehicle v/*, and possibly car-specified args...*/) {
    super(v);
    // ...fill in `Car`-specific information
}