java - 异常类不工作

Question

我有一个程序试图抛出某个异常。我在这里创建了一个自定义异常类:

import java.io.*;

public class ShapeException extends Exception
{
   public ShapeException(String message)
   {
      super(message);
   }
}

这是我尝试实现异常的类:

import java.io.*;

public class Circle
{      
   private double radius;  

   public Circle(double inRadius )
   {
      if(inRadius < 0.0)
      {
         throw new ShapeException("Shape Exception Occurred...");
      }
      else
      {
         radius = inRadius;
      }
   }

   public double getRadius()
   {
      return radius;
   }

   public void setRadius(double newRadius)
   {
      if(newRadius < 0.0)
      {
         throw new ShapeException("Shape Exception Occurred...");
      }
      else
      {
         radius = newRadius;
      }
   }

   public double area()
   {
      return Math.PI * radius * radius;
   }

   public void stretchBy(double factor )
   {
      if(factor < 0.0)
      {
         throw new ShapeException("Shape Exception Occurred...");
      }
      else
      {
         radius = radius * factor;
      }
   }

   public String toString()
   {
       return "Circle Radius: " + radius; 
   }
}

但是，这不会编译并给出错误，告诉我必须捕获或声明抛出我的形状异常错误。我究竟做错了什么？这不是声明了吗？

Answer 1

在java中，每当你抛出一个受检查的异常时，你需要在方法签名中使用throws关键字声明它。下面是没有任何编译错误的代码片段，因为每个方法在抛出 ShapeException 的地方都有 throws 声明。

public class Circle {
    private double radius;

    public Circle(double inRadius) throws ShapeException {
        if(inRadius < 0.0) {
            throw new ShapeException("Shape Exception Occurred...");
        } else {
            radius = inRadius;
        }
    }

    public double getRadius() {
        return radius;
    }

    public void setRadius(double newRadius) throws ShapeException {
        if(newRadius < 0.0) {
            throw new ShapeException("Shape Exception Occurred...");
        } else {
            radius = newRadius;
        }
    }

    public double area() {
        return Math.PI * radius * radius;
    }

    public void stretchBy(double factor) throws ShapeException {
        if(factor < 0.0) {
            throw new ShapeException("Shape Exception Occurred...");
        } else {
            radius = radius * factor;
        }
    }

    @Override
    public String toString() {
        return "Circle Radius: " + radius;
    }
}