# Task 

An abstract class called ``Shape`` has been created for you. It contains two abstract methods: ``calculateArea()`` and ``calculatePerimeter()``. Your task is to implement two classes: ``Rectangle`` and ``Circle``. You need to inherit these classes from the abstract class ``Shape`` and **override** its methods.
Here's a brief guide:

* For the ``Circle`` class, you will need fields such as `radius`, and for the `Rectangle` class, you will need fields like `width` and `height`. These fields and their constructors are **already provided for you**. Use these fields when overriding the methods.

* If you don't have strong geometry knowledge, here's a quick reference with formulas you need to use:
   *  Circle Area: **Pi * radius * radius**;
   * Circle Perimeter: **2 * PI * radius**;
   * Rectangle Area: **width * height**;
   * Rectangle Perimeter: **2 * (width + height)**.

To use the value of π (PI), make use of the ``Math`` library. You can use ``Math.PI`` to access the value of π.







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  <li>
    Use the <code>@Override</code> annotation to override both methods from the
    abstract class <code>Shape</code>: <code>calculateArea()</code> and
    <code>calculatePerimeter()</code>.
  </li>
  <li>
    For the <code>Circle</code>, utilize the <b>formulas I mentioned above</b>.
    To access the value of π, use <code>Math.PI</code>.
  </li>
  <li>Use the syntax <code>return "formula to calculate";</code>.</li>
  <li>
    Click the <b>Run Tests</b> button to check the correctness of your solution.
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// Circle class:
@Override
public double calculateArea() {
    return Math.PI * radius * radius;
}

@Override
public double calculatePerimeter() {
    return 2 * Math.PI * radius;
}

// Rectangle class:
@Override
public double calculateArea() {
    return width * height;
}

@Override
public double calculatePerimeter() {
    return 2 * (width + height);
}</textarea
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Those who know OOP can program well. That's what many programmers say. Get ready for an important part of your Java learning journey, mastering which will greatly boost your programming skills in general. You will learn how to effectively use the Java development environment, the principles of Object-Oriented Programming (OOP), and best practices in OOP. You will learn to make your code flexible and deepen your knowledge of previously covered topics. Let's get started!


Finally, we can start learning Object-Oriented Programming (OOP) in Java. It will be challenging, but I'm confident that you'll succeed! In this section, we'll cover all the principles of OOP, explain why OOP is important. You'll learn how to inherit classes, overload and override methods, encapsulate data from other classes, and work with abstraction. Moreover, you'll reinforce all these theoretical concepts with practical exercises, working on assignments in your IDE. You'll gain a wealth of knowledge, both practical and theoretical, so let's get started!

In the previous section, we concluded that all Object-Oriented Programming is mainly built on abstraction. However, an abstract class has one significant limitation – you can inherit from only one abstract class. But what if we need more?
Interfaces come to the rescue. In this section, you will learn what an interface is, why it's necessary, how to use it correctly, and you will continue practicing Object-Oriented Programming. Let's turn you into a professional!

Challenge: Abstraction

Task