try catch with InputMismatchException creates infinite loop

Question

So I m building a program which takes ints from user input  I have what seems to be a very straightforward try catch block which  if the user doesn t enter an int  should repeat the block until they do  Here s the relevant part of the code   import java util InputMismatchException  import java util Scanner    public class Except       public static void main String   args            Scanner input   new Scanner System in           boolean bError   true          int n1   0  n2   0  nQuotient   0           do               try                   System out println  Enter first num                      n1   input nextInt                    System out println  Enter second num                      n2   input nextInt                    nQuotient   n1 n2                  bError   false                             catch  Exception e                    System out println  Error                             while  bError            System out printf   d  d    d  n1 n2  nQuotient             If I enter a 0 for the second integer  then the try catch does exactly what it s supposed to and makes me put it in again  But  if I have an InputMismatchException like by entering 5 5 for one of the numbers  it just shows my error message in an infinite loop  Why is this happening  and what can I do about it   By the way  I have tried explicitly typing InputMismatchException as the argument to catch  but it didn t fix the problem

User · Answer

As the bError   false statement is never reached in the try block  and the statement is struck to the input taken  it keeps printing the error in infinite loop   Try using it this way by using hasNextInt    catch  Exception e                System out println  Error                input hasNextInt                         Or try using nextLine   coupled with Integer parseInt   for taking input      Scanner scan   new Scanner System in    int num1   Integer parseInt scan nextLine     int num2   Integer parseInt scan nextLine

User · Answer

To follow debobroto das s answer you can also put after   input reset    input next       I had the same problem and when I tried this  It completely fixed it

User · Answer

Limp  your answer is right  just use  nextLine   while reading the input  Sample code       do           try               System out println  Enter first num                  n1   Integer parseInt input nextLine                 System out println  Enter second num                  n2   Integer parseInt input nextLine                 nQuotient   n1   n2              bError   false            catch  Exception e                System out println  Error                     while  bError        System out printf   d  d    d   n1  n2  nQuotient     Read the description of why this problem was caused in the link below  Look for the answer I posted for the detail in this thread   Java Homework user input issue  Ok  I will briefly describe it  When you read input using nextInt    you just read the number part but the ENDLINE character was still on the stream  That was the main cause  Now look at the code above  all I did is read the whole line and parse it   it still throws the exception and work the way you were expecting it to work  Rest of your code works fine

User · Answer

another option is to define  Scanner input   new Scanner System in   inside the try block  this will create a new object each time you need to re-enter the values

User · Answer

To complement the AmitD answer   Just copy pasted your program and had this output   Error  Enter first num        infinite times        As you can see  the instruction   n1   input nextInt      Is continuously throwing the Exception when your double number is entered  and that s because your stream is not cleared   To fix it  follow the AmitD answer

User · Answer

You need to call next    when you get the error  Also it is advisable to use hasNextInt           catch  Exception e                System out println  Error                input next      Move to next other wise exception             Before reading integer value you need to make sure scanner has one  And you will not need  exception handling like that       Scanner scanner   new Scanner System in       int n1   0  n2   0      boolean bError   true      while  bError            if  scanner hasNextInt                n1   scanner nextInt            else               scanner next                continue                    if  scanner hasNextInt                n2   scanner nextInt            else               scanner next                continue                    bError   false            System out println n1       System out println n2     Javadoc of Scanner     When a scanner throws an InputMismatchException  the scanner will not pass the token that caused the exception  so that it may be retrieved or skipped via some other method

User · Answer

YOu can also try the following     do           try               System out println  Enter first num                  n1   Integer parseInt input next                  System out println  Enter second num                  n2   Integer parseInt input next                  nQuotient   n1 n2               bError   false                     catch  Exception e                System out println  Error                 input reset                    while  bError

[java] try/catch with InputMismatchException creates infinite loop

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