Define a class of Point in the 3D space, with consideration of varying constructors.

Define a class of Point in the 3D space, with consideration of varying constructors.

Define a class of Ball using the Point defined in Q1. The methods include the calculation of perimeter, area, and the distance to another ball or point.

Declare a point and a couple of balls, then sort the balls by the distance to the given point in the ascending order.

提供题目的中文意思，大概是类的定义。