Understanding How to Retrieve New Variable Values from an Inherited Class in Kotlin

Learn how to correctly access and utilize variable values in inherited classes through Kotlin. Understand the importance of calling super functions in inheritance.
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How to Get New Variable Value from an Inherited Class: A Kotlin Guide

Inheritance is one of the main pillars of Object-Oriented Programming (OOP), providing a way to create a new class based on an existing class. But sometimes, especially in languages like Kotlin, the process of accessing inherited variables can become confusing, especially when overridden methods are involved. In this post, we’ll unpack a common issue related to this and provide a clear solution.

The Problem

In the provided example, we have a Parent class and a Child class that inherits from it. The class has a protected variable z, which is intended to be assigned a value within a private method called getMyAge(). However, when getMyAge() is overridden in the Child class, the output leads to null. Here’s the relevant portion of the code causing confusion:

[[See Video to Reveal this Text or Code Snippet]]

Why Is This Happening?

The key reason for getting a null value lies in the fact that the Child class's version of getMyAge() does not call the getMyAge() method from the Parent class. Without this call, the variable z remains unset since the original logic to assign a value to z is never executed.

The Solution

To rectify this issue, you need to ensure that the overridden getMyAge() method in the Child class calls the getMyAge() method from the Parent class. Here’s how to correctly implement it:

Step-by-Step Implementation

Keep the Structure of the Parent Class: This class defines how z is calculated.

[[See Video to Reveal this Text or Code Snippet]]

Override the Method in the Child Class:
Here, you ensure that you call the parent’s getMyAge() method. This action allows z to be assigned the proper value before you attempt to print it.

[[See Video to Reveal this Text or Code Snippet]]

What This Accomplishes

Key Takeaways

Understand Visibility Modifiers: Protected variables are accessible in inherited classes but their values need to be set through methods if they are not initialized in the constructor or another method.

Debugging: When encountering null or unexpected values, check to ensure your parent methods are being invoked.

By following these guidelines, you can effectively manage inherited variables and ensure they behave as expected. Enjoy coding in Kotlin, and remember to leverage the power of inheritance wisely!