my codes goes infinity loop and does not prompts the user anymore

Question

boolean acceptPcode=true;
boolean acceptQty=false;
int Qty=0;
List<Integer> purchasedProdQty=new ArrayList<>();

while(acceptPcode==true && acceptQty==false){
        do{
            try{
                 System.out.print("Enter Qty: ");
                    Qty=sc.nextInt();
                    acceptQty=true;                 
              }catch(InputMismatchException ime){
                    System.out.println("Invalid quantity please enter a number!");
                    acceptQty=false;
              }

                    if(acceptQty==true)
                    purchaseProdQty.add(Qty);

           }while(acceptQty==false);

}

my question is that when i enter a letter it goes in an infinity loop and it doesn't prompt the user to enter a quantity ....which is

Enter Qty: Invalid quantity please enter a number!

Enter Qty: Invalid quantity please enter a number!......

@Josay. There is no exception. It's pretty clear from the question. — Mad Physicist, Feb 07 '14 at 15:37
The following question might help: http://stackoverflow.com/questions/21608990/creating-an-array-list-java/21609314#21609314 Its very similar. You loop until a condition. I feel it might be due to the lack of the second scanner. — TheOneWhoPrograms, Feb 07 '14 at 15:38
@MadPhysicist I am a bit confused here. How do we get "Invalid quantity please enter a number!" if we don't have an exception to catch ? — SylvainD, Feb 07 '14 at 15:41
@LuiggiMendoza. Possibly. The problem is pretty clearly with what sc is doing, so we need to know what it is without having to guess. — Mad Physicist, Feb 07 '14 at 15:41
Given the context, isn't it blatantly obvious that `sc` is a `Scanner`!? — Josh M, Feb 07 '14 at 15:43
@MadPhysicist AFAIK `Scanner` is the only class in Java SE that has a `nextInt` method to, uhm, read `int` input. — Luiggi Mendoza, Feb 07 '14 at 15:52
@LuiggiMendoza. I do not doubt that. I am just wondering how it is initialized. Is it wrapped around `System.in`? Is it a file scanner? I hate when people make you guess to debug their code. That being said, good answer. — Mad Physicist, Feb 07 '14 at 15:55
@MadPhysicist this statement: *`System.out.print("Enter Qty: ");`* answers your last comment. — Luiggi Mendoza, Feb 07 '14 at 15:56
@LuiggiMendoza. It implies an answer, yes. But the code is still very incomplete. — Mad Physicist, Feb 07 '14 at 15:57

score 3 · Accepted Answer · answered Feb 07 '14 at 15:42

You forgot to read the \n (or \r\n) characters that are from the next line. In your current code, the scanner is waiting for an int input, bu the current next input is this break line char. Just add sc.nextLine() in your code to consume the break line char:

Qty=sc.nextInt();
sc.nextLine();
acceptQty=true;

score 0 · Answer 2 · answered Feb 07 '14 at 15:42

0

From what I can gather it seems your scanner(sc) is throwing an exception. This causes acceptQty to constantly be false keeping you stuck in your inner do-while loop.

answered Feb 07 '14 at 15:42

jwang

633
1
5
12

Reimeus · Answer 3 · 2014-02-07T15:55:31.247

0

You need to consume any illegal characters in the exception block otherwise they won't be consumed by the Scanner#nextInt method call causing the loop to repeat itself indefinitely:

} catch(InputMismatchException ime) {
    System.out.println
      ("Invalid quantity: " + sc.nextLine() + " please enter a number ");
    ...
}

edited Feb 07 '14 at 15:55

answered Feb 07 '14 at 15:47

Reimeus

158,255
15
216
276

score 0 · Answer 4 · answered Feb 07 '14 at 19:46

0

You are getting exception while reading out of sc and so it always go into infinity loop. Can you paste what's the value assiged in sc?

answered Feb 07 '14 at 19:46

user3028989

87
13

score -1 · Answer 5 · answered Feb 07 '14 at 15:50

I believe you're doing this all wrong. Your method of validation is very obscure and can be simplified. Suppose you have the following method:

public int readNumber(final String prompt, final Scanner scanner){
    System.out.println(prompt);
    try{
        return scanner.nextInt();
    }catch(Exception ex){
        System.err.println("Enter a valid number");
        return readNumber(prompt, scanner);
    }
}

This method will print out the prompt (the first argument) and read input from the provided Scanner (the second argument). If the user enters something that can't be parsed as an int, it will invoke the same method (recursion).

Take out both of your loops and when you want to read an int from your Scanner, do something like:

int value = readNumber("Enter a quantity", sc);

You know for sure that Integer.MAX_VALUE >= value >= Integer.MIN_VALUE

my codes goes infinity loop and does not prompts the user anymore

5 Answers5