1.编写一个圆环类 Ring 的 Java 程序。圆环类有 3 个数据成员 , 分别是内半径 innerRadius, 外半径 outerRadius 和颜色 color, 这些属性可以查看 get 也可以重新设置 set, 另外 , 圆环还可以返回其面积 area 。

public class Ring {
    private double innerRadius;
    private double outerRadius;
    private String color;

    public Ring(double innerRadius, double outerRadius, String color) {
        this.innerRadius = innerRadius;
        this.outerRadius = outerRadius;
        this.color = color;
    }

    public double getInnerRadius() {
        return innerRadius;
    }

    public void setInnerRadius(double innerRadius) {
        this.innerRadius = innerRadius;
    }

    public double getOuterRadius() {
        return outerRadius;
    }

    public void setOuterRadius(double outerRadius) {
        this.outerRadius = outerRadius;
    }

    public String getColor() {
        return color;
    }

    public void setColor(String color) {
        this.color = color;
    }

    public double getArea() {
        return Math.PI * (Math.pow(outerRadius, 2) - Math.pow(innerRadius, 2));
    }
}

使用示例：

Ring ring = new Ring(5, 10, "red");
System.out.println("Inner radius:" + ring.getInnerRadius());
System.out.println("Outer radius:" + ring.getOuterRadius());
System.out.println("Color:" + ring.getColor());
System.out.println("Area:" + ring.getArea());

ring.setInnerRadius(4);
ring.setOuterRadius(9);
ring.setColor("blue");

System.out.println("Inner radius:" + ring.getInnerRadius());
System.out.println("Outer radius:" + ring.getOuterRadius());
System.out.println("Color:" + ring.getColor());
System.out.println("Area:" + ring.getArea());