Newb! Help with try/catch

[Dee Gx]

so I am doing a fraction exception test with a denominator is zero exception. everything compiles except the actual FractionExceptionTest which gives me one error in the catch which is: error: exception DenominatorIsZero is never thrown in body of corresponding try statement
           catch(DenominatorIsZero e)
           ^
1 error

I have found a plethora of reasons for this but am falling victim to information overload and am getting nowhere. Below are all 3 parts of the code.  hoping someone can help.  

Thanks in advance!!
MJ

import java.util.Scanner;

public class FractionExceptionTest 
{

    public static void main(String[] args) 
    {
        int num, den;
        boolean validDen = false;
        Scanner scan = new Scanner(System.in);
        Fraction f;
        
        while (validDen)
        {
            System.out.println("Enter the numerator: ");
            num = scan.nextInt();
                
            System.out.println("Enter the denominator: ");
            den = scan.nextInt();

            try 
            {
                if(den != 0)
                {
                    validDen = true;
                }
                
                f = new Fraction(num, den);
                System.out.println(f + " is a valid fraction.");
            } 

            catch(DenominatorIsZero e)
            {
                System.out.println(e.getMessage()); 
            }
              
        }
        
        System.out.println("Process completed.");
    }      
}   

public class DenominatorIsZero extends Exception
{
    public DenominatorIsZero()
    {
        super("Denominator must be greater than 0.");
    }
}

[Stephan van Hulst]

Welcome to CodeRanch, Dawn!

We can't really help you unless you post the full error message, and your Fraction class.

[Dee Gx]

oops.  sorry about that!  
here's my fraction class:

public class Fraction2
{

	  private int num;
     private int den;
     
     //default constructor
     public Fraction2 ()
     {
        num = 1; 
        den = 1;
     }
     
     public Fraction2 (int n, int d) throws DenominatorIsZero
     {
         num = n;
         den = d;
     }// constructor
  
     public void setN(int n) 
     {
         num = n;
     }// mutator

[Dee Gx]

geez.  sorry again for messing up.  guess I've become too frustrated with this :/

public class Fraction2
{

	  private int num;
     private int den;
     
     //default constructor
     public Fraction2 ()
     {
        num = 1; 
        den = 1;
     }
     
     public Fraction2 (int n, int d) throws DenominatorIsZero
     {
         num = n;
         den = d;
     }// constructor
  
     public void setN(int n) 
     {
         num = n;
     }// mutator

     public void setD(int d) throws DenominatorIsZero
     {
         if (d == 0) throw new DenominatorIsZero();
         den = d;
     }
    
     public int getN()
     {
         return num;
     }// accessor
     
     public int getD()
     {
         return den;
     }// accessor
    
     public String toString()
     {
         return "" + num + " / " + den;
     }
     
     public boolean equals(Fraction f)
     {
         return getN()*f.getD() == f.getN()*getD();     
     }
}

[Henry Wong]

Your test uses the Fraction class. You showed us the code for the Fraction2 class.

Henry

[Stephan van Hulst]

A few other remarks about your code:

You're declaring variables before they're being used. You should declare variables in the deepest scope possible, and initialize them in one go.

You don't have to pay per character. Write out identifiers: numerator instead of num, getNumerator() instead of genN().

Your test class' loop body will never run.

Dividing by zero is a bug, which should not be recoverable. DenominatorIsZero should be a RuntimeException.

Why do denominators have to be greater than zero? Isn't -2 a valid denominator?

Why do you provide a default fraction of 1/1?

Why does your fraction constructor not perform parameter checking?

Why does your fraction class have mutators?

Don't overload the equals() method. Either override the equals(Object) method, or give the method a different name.

[Dee Gx]

well that solved that problem.  I made so many versions trying different things I forgot to change Fraction to Fraction2.  So big thanks for that.  I always seem to miss the simple things.

but then a new problem popped it's ugly head out.  It's not letting me input the num and den.  As you can see I do have the scanner s....but it's not giving me the option to add input.  

[Stephan van Hulst]

That issue is raised in my third bullet point. Ask yourself why the loop is never run.

[Fred Kleinschmidt]

Your try block is too tightly placed.
scan.nextInt() can throw exceptions, so they should be inside the try clause rather than before it.

[Campbell Ritchie]

Stephan van Hulst wrote:. . .

Dividing by zero is a bug, which should not be recoverable. DenominatorIsZero should be a RuntimeException.

. . .

Agre; it should extend ArithmeticException and its name should end with Exception.
If a zero is passed to the constructor, you should throw an IllegalArgumentException. You should also describe that non‑zero requirement in a documentation comment.

[Leoncio Thiago]

Dawn Goxhaj wrote:so I am doing a fraction exception test with a denominator is zero exception. everything compiles except the actual FractionExceptionTest which gives me one error in the catch which is: error: exception DenominatorIsZero is never thrown in body of corresponding try statement
           catch(DenominatorIsZero e)
           ^
1 error

I have found a plethora of reasons for this but am falling victim to information overload and am getting nowhere. Below are all 3 parts of the code.  hoping someone can help.  

Thanks in advance!!
MJ

import java.util.Scanner;

public class FractionExceptionTest 
{

    public static void main(String[] args) 
    {
        int num, den;
        boolean validDen = false;
        Scanner scan = new Scanner(System.in);
        Fraction f;
        
        while (validDen)
        {
            System.out.println("Enter the numerator: ");
            num = scan.nextInt();
                
            System.out.println("Enter the denominator: ");
            den = scan.nextInt();

            try 
            {
                if(den != 0)
                {
                    validDen = true;
                }
                
                f = new Fraction(num, den);
                System.out.println(f + " is a valid fraction.");
            } 

            catch(DenominatorIsZero e)
            {
                System.out.println(e.getMessage()); 
            }
              
        }
        
        System.out.println("Process completed.");
    }      
}   

public class DenominatorIsZero extends Exception
{
    public DenominatorIsZero()
    {
        super("Denominator must be greater than 0.");
    }
}

Hi Dawn,

I would say try to always simplify your code. So, instead of using all these classes you can just take care of the denominator zero with the exception. Like this
              try {
int num1 = 30, num2 = 0;
int output = num1 / num2;
System.out.println("Result = " + output);
} catch (ArithmeticException e) {
System.out.println("[PhoneCoding.com-INFO LOG] Arithmetic Exception: You can't divide an integer by 0");
}


Simple is always better.

--Thiago

[Knute Snortum]

Simple is always better.  

Almost always.

Safety over Clarity

Clarity over Brevity

Brevity over all else