请问为什么第13行中的错误是未报告的异常，必须在声明声明为pr的情况下将其捕获

class Demo {
    public static void main(String args[]) {
        try {
            int x = 43 / 0;
        } catch (ArithmeticException ob) {
            throw ob;
        }

        try {
            int x = 43 / 0;
        } catch (Exception ob) {
            throw ob;
        }
        Exception ob = new Exception();
        throw ob;
        // Line 13 unreported exception Exception; must be caught or declared to be thrown
    }
}