Implement a Stock class

# Introduction

In this challenge, we will create a Java class named "Stock" to accurately represent and track the rise and fall of a stock. The class will have specific data fields such as stock code, stock name, and previous and current stock values. We will also implement a method to calculate and retrieve the percentage change in the stock value. Finally, we will write a test class to validate the implementation of the Stock class by creating an instance of it and displaying the percentage change in value.