Java 类泛型

Question

这个问题已经有答案了:

Is List<Dog> a subclass of List<Animal>? Why are Java generics not implicitly polymorphic? (19 个回答)

已关闭 5 年前。

如果我要使用以下代码，我有什么选择？

class Garage<X>{}

class Vehicle {}

class Car extends Vehicle {}

class Bike extends Vehicle {}

class A {
    public static void main(String[] args) {
        Garage<Car> car = new Garage<>();
        Garage<Bike> bike = new Garage<>();
        Garage<Vehicle> vehicle = new Garage<>();
        //what are the options to do this?
        vehicle=car;
        vehicle=bike;
    }
}

我追求的是尝试upcast(？)汽车和自行车到车辆。对于这种泛型类类型，这是否可能？

Answer 1

为了做你想做的事，你需要改变

Garage<Vehicle> vehicle = new Garage<>();

至

Garage<? extends Vehicle> vehicle = new Garage<>();