Thread: check for valid argument to a method

Hi,

I am a newbie and have just managed to make my first java program wokr I am now taking that program further to enable it do some error handling with throw -> try -> catch

I want the called method to handle the detection and calling method to handle the error. My problem is to write the proper syntax in java to check if the passed argument to called methods parameter is indeed a integer or not and then throw an exception. Here is the code that I have created:

import java.io.*;
import java.util.Scanner;
 
public class root {
 
	public static int calcRoot(int a)
	{
		 if (a != integer) //what is the proper syntax to check if the parameter is a integer?
		throw new intErrorExecption("Input must be a integer");
		return a=(int) Math.sqrt(a);
	}
 
 
	public static void main(String[] args) throws IOException 
	{
		int tempInt=0;
 
		String sCont;
		BufferedReader stdin = new BufferedReader
			      (new InputStreamReader(System.in));
		try{
 
		do 
		{
 
		System.out.print("Enter integer: ");
		System.out.flush();
		tempInt=Integer.parseInt( stdin.readLine());
 
		}  
 
	       catch (intErrorExecption e)
	       {System.out.println("ERROR: Only a integer is a valid input");
		 } 
 
 
	       System.out.println("The square root of " +tempInt+ " is "+calcRoot(tempInt));
 
 
 
	       System.out.print("Do you want to continue? (y / n): ");
 
 
	       System.out.flush();
 
 
			/* Code to check if the read line provided y or n, if y continue loop else
			 *  exit loop and print "Thank you for participating"
			 */
 
			sCont=stdin.readLine();
			 if(sCont.equals("n"))
			    {
			    	break;
 
			    }
 
			} while	(sCont.equals("y"));
 
 
 
		System.out.println("Thank you for participating");
 
 
	}
 
}

Thanks,
-Sohail

Actually I just want to check that the value passed to this methods argument is a integer at all? If not, I want the method to throw a exception and the the calling method to catch it handle it.

The point is more of a usability issue, I dont wont the user be presented by a compile time error, I want it gracefully handled. I want the user to be able to pass on whatever and then be presented by a error that makes sense.

I do see your point. If i comment out the if statement in my method and all the throw and try catch codes, I have no problems running the program as long as I feed it with integers, but if I submit a string value generates :

Enter integer: s
Exception in thread "main" java.lang.NumberFormatException: For input string: "s"
at java.lang.NumberFormatException.forInputString(Unk nown Source)
at java.lang.Integer.parseInt(Unknown Source)
at java.lang.Integer.parseInt(Unknown Source)
at root.main(root.java:28)

Is there anyway to catch this input and check it for a integer, if not then reply with a message that the input has to be a integer

I think that I have understood what you require. But before that let me point out that your do doesn't have an associated while.

If all that you wish to do is to print an appropriate message when the user enters an invalid integer, then you can catch the exception in the try catch block which will be automatically thrown by the calcRoot method. Your calcRoot method need not check if it is a String. If during run time, a String is passed instead of a number an exception will be generated automatically. So your code can simply be:

public static int calcRoot(int a)
	{
 
		return a=(int) Math.sqrt(a);
	}

In the main method you need to catch the exception as it might be generated by the calcRoot function. This is how your code structure needs tolook like:

public static void main(String[] args)
{
// accept value from user
try
{
// call calcSqrt function here and add whatever you want
}
catch(NumberFormatException e)
{
// process error by displaying an appriate message or do anything else that you want to do
}
}