Java - 为什么发送具体实现到通用接口,因为参数不能编译? [英] Java - why does sending concrete implementation to a generic interaface as parameter does not compile?
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问题描述
为什么 doSomething2()
和 doSomething3()
不能在Java中编译?
(丰田继续Car
和 Car实现ICar
)
public static void main(String [] args){
Map< String,Toyota> toyotas = new HashMap<>();
doSomething0(toyotas);
doSomething1(toyotas);
doSomething2(toyotas);
doSomething3(toyotas);
}
private static void doSomething0(Map< String,?extends Car> cars){}
private static void doSomething1(Map< String,?extends ICar> cars){ } b $ b private static void doSomething2(Map< String,Car> cars){}
public static void main(String [] args){
Map< String,Toyota> toyotas = new HashMap<>();
doSomething4(toyotas);
Toyota t = toyotas.get(hello); // b
private static void doSomething4(Map< String,Car> cars){
cars.put(Hello,new Honda());
}
Why
doSomething2()
anddoSomething3()
don't compile in Java?(
Toyota extends Car
andCar implements ICar
)public static void main(String[] args) { Map<String, Toyota> toyotas = new HashMap<>(); doSomething0(toyotas); doSomething1(toyotas); doSomething2(toyotas); doSomething3(toyotas); } private static void doSomething0(Map<String, ? extends Car> cars) {} private static void doSomething1(Map<String, ? extends ICar> cars) {} private static void doSomething2(Map<String, ICar> cars) {} private static void doSomething3(Map<String, Car> cars) {}
解决方案Because:
public static void main(String[] args) { Map<String, Toyota> toyotas = new HashMap<>(); doSomething4(toyotas); Toyota t = toyotas.get("hello"); // boom } private static void doSomething4(Map<String, Car> cars) { cars.put("Hello", new Honda()); }
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