编写一个自定义的异常类，包含一个product( )方法（用于两个数相乘），如果product( )方法中的两个参数的乘积小于0，则抛出一个自定义异常类的对象，输出错误信息和乘积的值。另外要求product( )方法要用throws关键字声明该方法要抛出自定义异常-Write a custom exception class that contains a product () method (for multiplying two numbers), if product () method of the product of the two parameters is less than 0, then throw a custom exception class object, output an error message and the product value. Also required product () method throws keyword to declare the method to use to throw custom exception