在overriden方法中删除throws，编译器在调用时需要try / catch块 [英] Removing throws in overriden method, compiler wants a try/catch block when invoking

问题描述

我有一个子类，我重写了继承的父方法：我从方法声明中删除了throws子句。

I have a subclass and I am overriding the inherited parent method: I am removing the throws clause from the method declaration.

现在，使用多态，我的实例是运行时类型应该确定方法实现;然而，当我尝试编译时，编译器抱怨并想要一个围绕方法调用的try / catch块，就像调用超类方法而不是子类版本一样？

Now, using polymorphism, the my instance's runtime type should determine the method implementation; yet, the compiler complains and wants a try/catch block around the method invocation when I try to compile, as if the superclass method is being invoked and not the subclass version?

我知道我可以删除throws声明或缩小已检查的异常，这可以在覆盖时抛出。为什么这仍然抛出异常？

I'm aware that I can remove the throws declaration or narrow down the checked exception which can be thrown when overriding. Why is this still throwing the exception?

class A{
    void foo()throws Exception{throw new Exception();}
}    

class SubB extends A{
    @Override
    void foo(){  System.out.println("B");  
}

public static void main(String[] args) {
    A a = new SubB();
    a.foo(); //compiler reports: unhandled exception type Exception 
}

推荐答案

编译器发送 A ，其中 抛出异常。如果您告诉编译器它是一个实际的 SubB 对象，它将停止抱怨

The compiler ses an A which does throw an Exception. If you however told the compiler it's an actual SubB object it will stop complaining

SubB b = new SubB();
b.foo();

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