java中一个简单的自定义异常

圆的pojo类

public  class Circle {
    //实体类pojo
    private double r;

    public Circle(double r) {
        this.r = r;
    }

    public Circle() {
    }

    public void setR(double r) {
        this.r = r;
    }

    public double getR() {
        return r;
    }
}

自定义异常类

public class CircleException extends  Exception{
    private String errMessage;
    public CircleException()
    {
    }

    public CircleException(String errMessage)
    {
        super(errMessage);
    }
}

测试类

public class TestCrcle {
    public static void main(String[] args){
        Scanner input=new Scanner(System.in);
        double r=input.nextInt();
        Circle circle=new Circle();
        circle.setR(r);
        try {
            double a=area(circle.getR());
            System.out.println(a);
        }catch (Exception e){
            System.out.println(e.toString());
        }

    }
    public static double area (double r) throws CircleException {
            if (r<=0){
            //向上抛到父类
              throw  new CircleException("您输入的半径必须大于零");
            }
           double area=3.14*r*r;
           return  area;
    }
}