Question

JAVA 定义一个圆类Circle

定义一个圆类Circle，其中：
radius属性表示半径，
calcArea方法用于计算圆的面积

Answer 1

public class Circle {
double radius;

public Circle(double rad) {
radius = rad;
}
public double calcArea() {
return Math.PI * radius * radius;
}
public static void main(String[] args) {
Circle c = new Circle(3);
System.out.println(c.calcArea());
}
}

追问

Circle c = new Circle(3);
里面的3是什么意思？

追答

形参啊，就是圆的半径的值

Answer 2

public class Circle {
private double radius;
public double calcArea(double r) {
double pi = 3.14;
return pi * r * r;
}
}