Cant seem to get my loop to work after catching an exception.

[lonnieg1214]

Sorry about that here's the edit:

I am trying to get user inputs (double types). so when i get a letter instead of a double i get an exception even though i had a while loop checking for this. so i looked up how to do exception handling and now when i get to that point it catches it but only outputs the message i gave and terminates instead of going through the while loop again. apparently there is no way to go back to before the error happened unless you use a while loop. but the loop isn't working it just terminates.

here's the code:

public static void collectInfo()
	{
 
	double firstW=0;
	double secondW=0;
	double payRate =0;
	double holiHours =0;
	boolean firstWGood = true;	 
	boolean secondWGood = true;
	boolean payRateGood = true;
	boolean holiHoursGood = true;
 
		Scanner in = new Scanner (System.in);
		do{
			try{
			System.out.println("Enter hours received for the first week of your paycheck. ");
			System.out.println("If you have overtime, just add it to this for example: 3 hours of overtime is 43 hours that week");
 
		firstW = in.nextDouble();
		firstWGood = false;
} catch (InputMismatchException e){
	System.out.println("Oops...");
 
}	
		}while(!firstWGood);

and here's the output when i ran the program(console):

Enter hours received for the first week of your paycheck.
If you have overtime, just add it to this for example: 3 hours of overtime is 43 hours that week
h
Oops...

[Norm]

Please edit your post and wrap your code with code tags:
[code=java]
YOUR CODE GOES HERE
[/code]
to get highlighting and preserve formatting.

instead of going through the while loop again.

What would keep the loop executing? What is the value of the variable need to be? What is its value when the loop starts? The code doesn't show it.

[lonnieg1214]

Sorry i'm new to all of this.

[Norm]

The while() loop will continue to execute as long as the expression inside of the loop has a true value.
What was the value of the expression in the while loop when it executed? For the loop to exit it must be false.

What value of firstWGood will allow the loop to exit?
What value of firstWGood will keep the loop looping?

What was the value of firstWGood when the loop started executing?

Do you know what the ! operator does with a boolean value?

What happens when a good value is entered and there is no exception?

[lonnieg1214]

The while() loop will continue to execute as long as the expression inside of the loop has a true value.
What was the value of the expression in the while loop when it executed? For the loop to exit it must be false.

What value of firstWGood will allow the loop to exit?
What value of firstWGood will keep the loop looping?

What was the value of firstWGood when the loop started executing?

Do you know what the ! operator does with a boolean value?

What happens when a good value is entered and there is no exception?

The way that the code is setup now it won't loop at all I wanted it to loop back to give the user another chance to put in the right info.
The ! Should make it false right? And since firstWGood started with true, that should make it loop back right?

[GregBrannon]

If firstWord is true, then !firstWord is false, and the do/while loop will end. The sample run you posted confirmed that.

Don't question the results, question the logic that provided the results.

[lonnieg1214]

If firstWord is true, then !firstWord is false, and the do/while loop will end. The sample run you posted confirmed that.

Don't question the results, question the logic that provided the results.

Ahh ok I keep getting confused on the loop so I start off with it being true and I want it to remain true if the user puts in the right info. But when they cause an exception, I changed the true to false to match the while condition so it would loop over. I have also tried it another way but it keeps looping over and over in an infinite loop. It seems to keep the entry that the user provided instead of getting rid of it and really starting over. How can I get the system to forget the entry and just retry the same portion. I have seen examples of just starting the whole thing over but I don't want to do that if the user is on the last entry and has to start over.

I think I have an idea when it catches the exception maybe I could have it default to a number like -1 and have the loop condition to repeat if it's less than 0?

[GregBrannon]

But when they cause an exception, I changed the true to false to match the while condition so it would loop over.

You can use the catch{} block to achieve this. Your code indenting is also funky, causing the code to be harder to read:

do
{
    // reset the repeat flag
    firstWGood = true;
 
    try
    {
        System.out.println("Enter hours received for the first week of your paycheck. ");
        System.out.println("If you have overtime, just add it to this for example: 3 hours of overtime is 43 hours that week");
 
        firstW = in.nextDouble();
    }
    catch (InputMismatchException e)
    {
        // the entry was improper, so try again
        firstWGood = false;
        System.out.println("Oops...");
 
    }
 
}while(!firstWGood);

With this design, you can adjust the true/false flag name and value to be more intuitive - or maybe you're happy with the way they are.

[Norm]

when they cause an exception, I changed the true to false

Look at the code. Does it do that?

EDIT: Looks like Greg has fixed it for you.

[lonnieg1214]

i tried what Greg did just now but it goes into an eternal loop

--- Update ---

right before i tried Greg's solution, i tried restarting the method when the exception occurred. that worked but that would suck for the user if they get to the fourth question and enter a letter on accident and then they will have to start all over again.

[Norm]

goes into an eternal loop

Can you copy the first part of the console showing what was entered and what the code printed out?

Read the API doc for the nextDouble() method to see what it does:
when there is good data
when there is bad data

Hint: the bad data is left in the buffer.

[lonnieg1214]

Enter hours received for the first week of your paycheck.
If you have overtime, just add it to this for example: 3 hours of overtime is 43 hours that week
h
Oops...

this is how it would go but then it will keep outputting this:

Enter hours received for the first week of your paycheck.
If you have overtime, just add it to this for example: 3 hours of overtime is 43 hours that week
Oops...
Enter hours received for the first week of your paycheck.
If you have overtime, just add it to this for example: 3 hours of overtime is 43 hours that week
Oops...

[GregBrannon]

Post your updated loop or method - enough to see the changes you made.

[Norm]

Did you read and understand the rest of my post#11?

[lonnieg1214]

is it possible to override anything to get the response i want? maybe overriding the error so it doesn't keep the bad data? that explains why it keeps looping

[Norm]

so it doesn't keep the bad data

You can use another Scanner class method to read the bad data from the Scanner's buffer.
For debugging you should also print out a message showing the bad data that was read.

[lonnieg1214]

here is what i changed it to which works but isn't ideal from a user's standpoint:

public static void collectInfo()
	{
 
	double firstW=0;
	double secondW=0;
	double payRate =0;
	double holiHours =0;
	boolean firstWGood = true;	 
	boolean secondWGood = true;
	boolean payRateGood = true;
	boolean holiHoursGood = true;
 
		Scanner in = new Scanner (System.in);
 
			try{
			System.out.println("Enter hours received for the first week of your paycheck. ");
			System.out.println("If you have overtime, just add it to this for example: 3 hours of overtime is 43 hours that week");
 
		firstW = in.nextDouble();
 
} catch (InputMismatchException e)
{
	UserInputs.collectInfo();
	System.out.println("Oops...");	
}	
 
 
}

--- Update ---

here's what i read but i don't see where it talks about the buffer but i did hear about the buffer you spoke about from stack overflow

nextDouble
public double nextDouble()
Scans the next token of the input as a double. This method will throw InputMismatchException if the next token cannot be translated into a valid double value. If the translation is successful, the scanner advances past the input that matched.
If the next token matches the Float regular expression defined above then the token is converted into a double value as if by removing all locale specific prefixes, group separators, and locale specific suffixes, then mapping non-ASCII digits into ASCII digits via Character.digit, prepending a negative sign (-) if the locale specific negative prefixes and suffixes were present, and passing the resulting string to Double.parseDouble. If the token matches the localized NaN or infinity strings, then either "Nan" or "Infinity" is passed to Double.parseDouble as appropriate.

Returns:
the double scanned from the input
Throws:
InputMismatchException - if the next token does not match the Float regular expression, or is out of range
NoSuchElementException - if the input is exhausted
IllegalStateException - if this scanner is closed

--- Update ---



I think i got it based on your guys advice here's what i came up with:

do
		{
 
			System.out.println("Enter hours received for the first week of your paycheck. ");
			System.out.println("If you have overtime, just add it to this for example: 3 hours of overtime is 43 hours that week");
try
{
		firstW = in.nextDouble();
 
			break;
 
} catch (InputMismatchException e)
{
	//UserInputs.collectInfo();
	in.next();
	System.out.println("oops... you may want to try to enter a number");	
}
		}
		while(!in.hasNextDouble());
 
 
}

let me know what you think also this is a static method that i was working on was that a good idea to implement?

[Norm]

If the translation is successful, the scanner advances past the input that matched.

From that I assume that if the translation is NOT successful, the scanner does NOT advance, ie it leaves the bad data in the buffer.

I used buffer in the generic sense referring to a place in the class where it reads data entered by the user (or from a file) and then scans over it as the program requests parts of it via the different Scanner class methods.

Using a recursive call is not the way to handle the problem. A loop with some variables should handle it.