java - Scanner 类放在哪里

Question

作为 Java 的新学生，我一直在练习编写方法，然后从不同的类中调用它们。我想知道如何由用户输入确定半径。我知道我需要使用 Scanner 类，但我不确定将 Scanner 导入哪个类以及在哪里放置以下代码。

Scanner userInput = new Scanner(System.in);
System.out.println("Please enter radius");
int radius = userInput.nextInt();

第一个文件 - 我的方法

package circle;

public class Circle {
  private double radius;
  final double pi;

  public Circle(double radiusIn, double piIn) {
    radius = radiusIn;
    pi = piIn;
  }

  public double getRadius() {
    return radius;
  }

  public double calculateDiameter() {
    return radius + radius;
  }

  public double calculateCircumference() {
    return 2 * pi * radius;
  }

  public double calculateArea() {
    return pi * radius * radius;
  }
}

第二个文件

package circle;

public class CircleTest {
  public static void main(String[] args) {
    Circle myCircle;
    myCircle = new Circle(3, 3.14159);
    System.out.println("Circle radius is " + myCircle.getRadius());
    System.out.println("Circle diameter is " + myCircle.calculateDiameter());
    System.out.println("Circle circumference is "
        + myCircle.calculateCircumference());
    System.out.println("Circle area is " + myCircle.calculateArea());
  }
}

Answer 1

通常，您可以在需要的地方声明变量，在这种情况下，这意味着在 main 方法中进行其余的用户交互。

package circle;

public class CircleTest {
  public static void main(String[] args) {
    Circle myCircle;

    Scanner userInput = new Scanner(System.in);
    System.out.println("Please enter radius");
    int radius = userInput.nextInt();

    myCircle = new Circle(radius);
    System.out.println("Circle radius is " + myCircle.getRadius());
    System.out.println("Circle diameter is " + myCircle.calculateDiameter());
    System.out.println("Circle circumference is "
        + myCircle.calculateCircumference());
    System.out.println("Circle area is " + myCircle.calculateArea());
  }
}

此外，Math.PI 是 pi 的更精确的近似值。使用它而不是依赖用户传递正确的值:

package circle;

public class Circle {
  private double radius;


  public Circle(double radiusIn) {
    radius = radiusIn;
  }

  public double getRadius() {
    return radius;
  }

  public double calculateDiameter() {
    return radius + radius;
  }

  public double calculateCircumference() {
    return 2 * Math.PI * radius;
  }

  public double calculateArea() {
    return Math.PI * radius * radius;
  }
}