Скачать или смотреть Why is Circle Class in Java Not Returning the Expected Area?

Discover the reasons why your Java `Circle` class might be returning an area of 0.0 instead of the expected value, and learn the best practices for calculating the area of a circle correctly.
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This video is based on the question https://stackoverflow.com/q/67498408/ asked by the user 'Vedprakash Maliarya' ( https://stackoverflow.com/u/15903594/ ) and on the answer https://stackoverflow.com/a/67498801/ provided by the user 'Renis1235' ( https://stackoverflow.com/u/7954021/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Understanding the Issue with the Circle Class in Java

If you're learning Java and have tried to create a class to calculate the area of a circle, you might have faced a frustrating problem: the area is being calculated incorrectly—returning 0.0 instead of the expected value like 78.5 for a radius of 5. This is a common stumbling block for beginners, and in this post, we'll break down the problem and provide a solution that both works and follows best practices in Java coding.

The Problem

In your code, you've created a Circle class with a field for the radius but are encountering unexpected behavior when trying to calculate the area. Let's take a look at the existing code that you are trying to use:

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

When you run this code and enter 5 as the radius, the output you see is:

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

Why is this Happening?

The issue lies in how the area is calculated within the Circle class. The calculation for the area Math.PI * r * r is done at the point of variable declaration, using the initial value of r, which is 0.0 (the default for uninitialized double values in Java). Since the variable r hasn't been set yet (you are assigning it later in the main method), the area calculation translates to:

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

This results in 0.0, leading to your unexpected output.

The Solution

To fix this issue, we need to calculate the area dynamically instead of during variable initialization. Let's implement some changes that adhere to best practices in Java.

Revised Circle Class

Here's a recommended structure for the Circle class:

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

Updated Main Class

Now, let's update the main method accordingly:

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

Summary of Changes

Calculate Area Dynamically: The area is now calculated within a method, ensuring it uses the current value of the radius.

Use Constructor for Initialization: The constructor assigns the input radius upon object creation.

Encapsulation: The radius field is marked private, following best practices for encapsulation.

By implementing these changes, your Java code should now correctly calculate and display the area of the circle based on the radius you input. This approach not only fixes the issue but also paves the way for better programming practices in object-oriented programming.

Now, you can run your program again, enter 5, and see the expected result of 78.53981633974483 for the area of the circle. Happy coding!