java无法为圆自身的异常创建半径异常

Question

异常无法出现，我显然不知道问题出在哪里。我想对圆半径做个例外。例如，如果我的输入为负值，则需要出现异常。我上了三节课。测试圈。爪哇，圆圈。java和非法的RadiuseException。爪哇

测试圈。爪哇

package circle;
public class TestCircle {

public static void main(String[] args) {

    double newRad;

    try {

        Circle A = new Circle();

        A.InputRadius();
        A.Calculation();
        newRad = A.getRadius();
        A.Result();
    } catch (IllegalRadiusException e) {
        System.out.println(e);
    }
}
}

圈。爪哇

package circle;

import java.util.Scanner;
public class Circle {

Scanner input = new Scanner(System.in);
private double radius;
private double area;

//this is consturctor method
public Circle() throws IllegalRadiusException {
    if (radius >= 0) {
        this.radius = radius;
        this.area = area;
    } else {
        throw new IllegalRadiusException("Radius Cannot be Negative");
    }
}

public void setRadius(double radius) {
    this.radius = radius;
}

public double getRadius() {
    return radius;
}

public void setArea(double area) {
    this.area = area;
}

public double getArea() {
    return area;
}

//------------------------------------------------------------//
public void Calculation() {
    area = 3.142 * radius * radius;
}

public void InputRadius() {
    System.out.print("Radius: ");
    radius = input.nextDouble();

}

public void Result() {
    System.out.println("");
    System.out.println("Radius: " + radius);
    System.out.println("Area: " + area);
}
}

非法辐射例外。爪哇

package circle;
public class IllegalRadiusException extends Exception {

//Extra kena tambah 'extends Exception'
//WAJIB KENA LETAK untuk CREATE OWN EXCEPTION
public IllegalRadiusException() {

    super();

}

public IllegalRadiusException(String message) {

    super(message);
}
}