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Thread: catch negative numbers

  1. #1
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    Default catch negative numbers

    Hello,
    I do not understand what is wrong in my code. I am trying to catch negative values, but the program is just running as normal, accepting them.
    package perfectSquareException2;
     
    import java.lang.*;
    import java.util.Scanner;
     
    public class perfSqEx {
     
     
     
     
    			public static void main(String args[] ) {
     
    			Scanner in= new Scanner(System.in);
    			double number = 0;
    			double a = 0;
    			boolean square = true;
    			boolean correct = false;
     
     
    			System.out.println("Enter positive number: ");
    			try {
    			number = in.nextDouble();
    			if (number > 0)
    				correct = true;
     
    			}catch (Exception exception) {
    				if (number < 0)
    				System.err.println(exception.getMessage() + "\n");
     
    		 }
     
    			if((Math.sqrt(number) * 10) % 10 == 0.0 ) {
     
    				square = true;
    					System.out.println("yes");
     
    				}else
    				{
    					square = false;
    					System.out.println("no");
    				}
     
    }
    }


    --- Update ---

    I know that I can create my own exception that will inherit general Exceptions class. Bt in this task I have to use exactly try catch block with the exception of type Exception.


  2. #2
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    Default Re: catch negative numbers

    There currently is no reason for your logic to enter the catch block, because there's nothing in the try{} block that can throw an exception. You might review this tutorial for pointers.

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    Default Re: catch negative numbers

    Thanks for reply, Greg.
    However, I am sure it can be done. I might have wrong coding for that or even wrong order. What i am trying to say in this program:
    the users tries to enter numbers and once negative number is entered, the system should catch the number and throw the exception.

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    Default Re: catch negative numbers

    Did you look at the tutorial I sent you?

    Of course it can be done, and I know what you're trying to say. You said it well the first time, but I'm not certain you hear so well. "The System" doesn't just throw unchecked exceptions by itself and this isn't even an unchecked exception. You just want to throw one, and that's fine, but where do you throw the exception? Read the tutorial and learn how to throw an exception. Something like:
    try
    {
        if ( this bad thing happens )
        {
            throw an exception
        }
    }
    catch
    {
        deal with the exception
    }

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    Default Re: catch negative numbers

    Quote Originally Posted by GregBrannon View Post
    There currently is no reason for your logic to enter the catch block, because there's nothing in the try{} block that can throw an exception.
    Yes there is, the call to nextDouble. The issue with the code is that the if statement handling the negative number is in the catch statement but a negative number will not cause an exception.
    Improving the world one idiot at a time!

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    Default Re: catch negative numbers

    I must be wearing a "Junky Kick Me" sign tonight.

    You're absolutely right. I was wrong. I believe I was thinking, " . . . there's nothing in the try{} block that can throw an exception . . . " if the user enters a negative number. I apologize if I misled the OP or caused anyone confusion by being imprecise in my response. I'll be waiting in the woodshed.

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    Default Re: catch negative numbers

    Quote Originally Posted by GregBrannon View Post
    I'll be waiting in the woodshed.
    Chop some wood while you're in there.
    Improving the world one idiot at a time!

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