Scanner error with nextInt()

Question

I am trying to use Scanner to get an int from the keyboard, but I getting the following error:

Exception in thread "main" java.util.NoSuchElementException
    at java.util.Scanner.throwFor(Scanner.java:907)
    at java.util.Scanner.next(Scanner.java:1530)
    at java.util.Scanner.nextInt(Scanner.java:2160)
    at java.util.Scanner.nextInt(Scanner.java:2119)
    at TableReader.mainMenu(TableReader.java:122)
    at TableReader.main(TableReader.java:76)

This is what I have. It is independent of the rest of my program, I don't understand why this isn't working. It is declared in a method that is being called in a while loop, if that helps.

    // scan for selection
    Scanner s = new Scanner(System.in);
    int choice = s.nextInt();           // error occurs at this line
    s.close();

I stepped through with the debugger and narrowed the error down to:

A fatal error has been detected by the Java Runtime Environment: SIGSEGV (0xb) at pc=0xb6bdc8a8, pid=5587, tid=1828186944

JRE version: 7.0_07-b30 Java VM: OpenJDK Server VM (23.2-b09 mixed mode linux-x86 ) Problematic frame: V [libjvm.so+0x4258a8] java_lang_String::utf8_length(oopDesc*)+0x58

Failed to write core dump. Core dumps have been disabled. To enable core dumping, try "ulimit -c unlimited" before starting Java again

Hunter McMillen · Accepted Answer · 2012-10-11T04:11:51.527

23

You should use the hasNextXXXX() methods from the Scanner class to make sure that there is an integer ready to be read.

The problem is you are called nextInt() which reads the next integer from the stream that the Scanner object points to, if there is no integer there to read (i.e. if the input is exhausted then you will see that NoSuchElementException)

From the JavaDocs, the nextInt() method will throw these exceptions under these conditions:

InputMismatchException - if the next token does not match the Integer regular expression, or is out of range
NoSuchElementException - if input is exhausted
IllegalStateException - if this scanner is closed

You can fix this easily using the hasNextInt() method:

Scanner s = new Scanner(System.in);
int choice = 0;

if(s.hasNextInt()) 
{
   choice = s.nextInt();
}

s.close();

edited Oct 11 '12 at 04:11

answered Oct 11 '12 at 04:05

Hunter McMillen

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This sends me into an infinite loop because what is within the brackets never gets called – spatara Oct 11 '12 at 04:08
@spatara Yes it checks to see if whatever the next item that the Scanner is pointing to can successfully be converted to an integer, if it can then `hasNextInt()` will return true, otherwise it will return false. – Hunter McMillen Oct 11 '12 at 04:09
I am just reading from the keyboard, there is no nextInt when the method is called – spatara Oct 11 '12 at 04:12
I am still stuck...hasNextInt() is returning false because it checks before I type the int... – spatara Oct 11 '12 at 04:20
@spatara It tries to interpret whatever you print as an integer – Hunter McMillen Oct 11 '12 at 04:20
but it does not interpret anything...it sees nothing, Do I understand this correctly? If I havent typed anything, hasNextInt() will return false, no? – spatara Oct 11 '12 at 04:22
`hasNextInt()` will wait for your input. Did you try it? – Hunter McMillen Oct 11 '12 at 04:28
yes, and I get an infinite loop...maybe something else is wrong. – spatara Oct 11 '12 at 04:36
@spatara.. See my post to get how not to get into an infinite loop.. – Rohit Jain Oct 11 '12 at 04:36

Scanner error with nextInt()

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