java - 在 Java 中从父类调用子类构造函数

Question

所以我正在学习 java 继承，但我遇到了一种我不知道如何解决的情况。

我想做的是从父类(super class)中调用子类构造函数。我不知道这是否有意义，但我会尝试用一个例子来解释我自己。

public class Phone {
    private String brand;
    private int weight;

    public Phone(String brand, int weight) {
        this.brand = brand;
        this.weight = weight;
    }

    public Phone(String brand, int weight, String tech) {
        // Here it is where I'm stuck
        // Call SmartPhone constructor with all the parameters
    }
}

public class SmartPhone extends Phone {
    private String tech;

    public SmartPhone(String Brand, int weight, String tech) {
        super(brand, weight);
        this.tech = tech;
    }
}

我为什么要这样做？

我希望能够不必在主要方面与智能手机打交道。
我希望能够做到:

Phone nokia = new Phone("Nokia", 295); // <- Regular Phone Instance
Phone iphone = new Phone("iPhone", 368, "4G"); // <- SmartPhone instance

Answer 1

Phone iphone = new Phone("iPhone", 368, "4G"); // <- SmartPhone instance

这毫无意义。如果你想要一个SmartPhone实例，你必须调用

Phone iphone = new SmartPhone("iPhone", 368, "4G");

您不能从父类(super class)构造函数调用子类构造函数。

如果你想让Phone的类型由传递的参数决定，你可以使用静态工厂方法:

public class PhoneFactory {

    public static Phone newPhone (String brand, int weight) {
        return new Phone(brand, weight);
    }

    public static Phone newPhone (String brand, int weight, String tech) {
        return new SmartPhone(brand, weight, tech);
    }
}

Phone nokia = PhoneFactory.newPhone("Nokia", 295); // <- Regular Phone Instance
Phone iphone = PhoneFactory.newPhone("iPhone", 368, "4G"); // <- SmartPhone instance