Question

What is the problem here? I am just simply trying to catch a custom exception depending on a if statement in my constructor, the entire code

/*
 * To change this template, choose Tools | Templates
 * and open the template in the editor.
 */
package question3_test;

/**
 *
 * @author jackandjill
 */
public class Triangle2 
{
    private int side1, side2, side3;
    private  double area;
    private  String message;    

    public  int getSide1()
    {
        return side1;
    }

    public void setSide1(int s1)
    {
        side1 = s1;
    }

    public  int getSide2()
    {
        return side2;
    }

    public void setSide2(int s2)
    {
        side2 = s2;
    }

    public  int getSide3()
    {
        return side3;
    }

    public void setSide3(int s3)
    {
        side3 = s3;
    }

   public Triangle2(int a,int b,int c) throws InvalidValueException
   {
    setSide1(a);
    setSide2(b);
    setSide3(c);

    try
    {
         if (!(side1 + side2 > side3) && (side2 + side3 > side1)&& (side1 + side3 > side2))

                 throw new InvalidValueException("Invalid Value");
    }
    catch (InvalidValueException excep)
    {
        message = excep.getMessage();
        //throw new InvalidValueException(message);
    }

    public double findArea(int side_1, int side_2, int side_3)
    {
        int s, a, b,c;
        a = side_1;
        b = side_2;
        c = side_3;
        s = ((a + b + c)/2);
        area = Math.sqrt(s*(s-a)*(s-b)*(s-c));
        //area =
        return area;
    }
   }
}

The problem is at my catch statement, it is underlined in red and says never thrown in the corresponding try statement

Answer 1

You can’t throw an Exception class like in the below code: –

throw InvalidValueException;

You have to make a new instance of your exception, and then throw it: –

throw new InvalidValueException();

But, still there is some logic problem in your code. You have declared your Exception to be throws, but at the same time, you are handling it in the catch block itself. Why would you do that?

UPDATE: –

As per your modified post: –

try
{
   if (!(side1 + side2 > side3) && (side2 + side3 > side1) && 
        (side1 + side3 > side2))

       message = "Invalid Triangle";

} catch (InvalidValueException e) {
    message = "Invalid Traingle";
}

Since you are no-where throwing any Exception in your try block, the catch block will complain about that..

If you want to throw an exception and catch it in place, use it like this: –

public Triangle2(int a,int b,int c) throws InvalidValueException

      if (!(side1 + side2 > side3) && (side2 + side3 > side1) && 
            (side1 + side3 > side2))

           throw new InvalidValueException("Invalid Value")
}

And suppose you are using it from your main method, you should have a try-catch block there, to handle the declared exception in constructor.: –

public static void main(String[] args) {
    Triangle triangle = null;
    try {
         triangle = new Triangle(2, 3, 4);
    } catch (InvalidValueException e) {
        e.printStackTrace();
    }
}

If you handle the exception in your method only, you should not declare it in your method declaration.. But if you are not handling it, then you must declare that exception to be thrown.

An exception should be either handled, or declared to be thrown (In which case, you should actually throw that exception), but never both

See This tutorial for more about Exception: – http://docs.oracle.com/javase/tutorial/essential/exceptions/catchOrDeclare.html