Requirement

In this Assignment, you should write a class that, given a circles radius, has methods that return the circles area, diameter, and circumference.
In case you have forgotten, the equations for a circles area, diameter, and circumference is given below.

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area = rr
diameter = 2r
circumference = 2r

Based on Chapter 3, Programming Challenge # 8 Circle class in your textbook. Your output is given below.

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Enter the radius of a circle: 5.3
The circle's area is            88.2472631
The circle's diameter is        10.6
The circle's circumference is   33.300854

Write a separate class called CircleDemo with a main method that asks the user for the circles radius, creates a Circle object, and then reports the circles area, diameter, and circumference using the circles getter methods.

Analysis

本题需要的数学背景见Pi，需要实现一个Circle类，以及对应的方法，如setRadius()，getRadius()，getArea()，getDiameter()，getCircumference()。
本题较为简单，注意数据类型，精度以及输入输出格式即可。

Tips

下面是ClicleDemo类的实现

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class CircleDemo {
  private double radius;
  private static final PI = 3.14159;

  public CircleDemo() {}

  public void setRadius() {
    this.radius = radius;
  }

  public double getRadius() {
    return this.radius;
  }

  public double getArea() {
    return CircleDemo.PI * this.radius * this.radius;
  }

  public double getDiameter() {
    return 2 * this.radius;
  }

  public double getCircumference() {
    return 2 * CircleDemo.PI * this.radius;
  }
}