idea :跟着"任亮"做练习题 21,异常

/*idea :跟着"任亮"做练习题 21,异常;
计算圆的面积,通过自定义异常来设计,半径不能为零和负数,采用异常机制处理

一;创建构造器:;
homework家庭作业*/
package cn.tx.homework;
//ValidData有效数据;ValidDataExceotion非法数据异常
public class ValidDataExceotion extends RuntimeException{
//继承父类构造器 Ctrl+O; 用Shift选前5个
public ValidDataExceotion() {
super();
}

public ValidDataExceotion(String message) {
    super(message);
}

public ValidDataExceotion(String message, Throwable cause) {
    super(message, cause);
}

public ValidDataExceotion(Throwable cause) {
    super(cause);
}

protected ValidDataExceotion(String message, Throwable cause, boolean enableSuppression, boolean writableStackTrace) {
    super(message, cause, enableSuppression, writableStackTrace);
}

}

二:创建方法
package cn.tx.homework;

import java.util.Scanner;

public class Demo {
//计算面积;建立一个方法;getArea获得面积; area面积;
public static double getArea(double r){
//面积初始值
double area = 0;
//抛出异常
if (r<=0) {
throw new ValidDataExceotion(“半径不可以是负或零”);
}
//Math 类包含用于执行基本数学运算的方法，如初等指数、对数、平方根和三角函数。
area = Math.PIrr;
return area;

}

public static void main(String[] args) {
    //Scanner键盘输入
    Scanner s = new Scanner(System.in);
    System.out.println("请输入圆的半径");
    int r = s.nextInt();
    double area = 0;
    try {
        //area = getArea(10);抛出异常ctrl+alt+t
        area = getArea(r);
        System.out.println("圆的面积是:"+area);
    } catch (Exception e) {
       if (e instanceof ValidDataExceotion){
           System.out.println("传递的参数错误.请重新输入");
            r= s.nextInt();
           area = getArea(r);
           System.out.println("圆的面积是:"+area);
       }
    }

}

}