NoSuchElementException with Java.Util.Scanner

问题

I am very new to Java but am working through the book Java: How to program (9th ed.) and have reached an example where for the life of me I cannot figure out what the problem is.

Here is a (slightly) augmented version of the source code example in the textbook:

import java.util.Scanner;
public class Addition {
  public static void main(String[] args) {
    // creates a scanner to obtain input from a command window

    Scanner input = new Scanner(System.in);

    int number1; // first number to add
    int number2; // second number to add
    int sum; // sum of 1 & 2

    System.out.print(\"Enter First Integer: \"); // prompt
    number1 = input.nextInt(); // reads first number inputted by user

    System.out.print(\"Enter Second Integer: \"); // prompt 2 
    number2 = input.nextInt(); // reads second number from user

    sum = number1 + number2; // addition takes place, then stores the total of the two numbers in sum

    System.out.printf( \"Sum is %d\\n\", sum ); // displays the sum on screen
  } // end method main
} // end class Addition

I am getting the \'NoSuchElementException\' error:

Exception in thread \"main\" java.util.NoSuchElementException
at java.util.Scanner.throwFor(Scanner.java:838)
at java.util.Scanner.next(Scanner.java:1461)
at java.util.Scanner.nextInt(Scanner.java:2091)
at java.util.Scanner.nextInt(Scanner.java:2050)
at Addition.main(Addition.java:16)
Enter First Integer:

I understand that this is probably due to something in the source code that is incompatible with the Scanner class from java.util, but I really can\'t get any further than this in terms of deducing what the problem is.

回答1:

NoSuchElementException Thrown by the nextElement method of an Enumeration to indicate that there are no more elements in the enumeration.

http://docs.oracle.com/javase/7/docs/api/java/util/NoSuchElementException.html

How about this :

if(input.hasNextInt() )
     number1 = input.nextInt(); // if there is another number  
else 
     number1 = 0; // nothing added in the input

回答2:

You should use hasNextInt() before assigning value to variable.

回答3:

NoSuchElementException will be thrown if no more tokens are available. This is caused by invoking nextInt() without checking if there's any integer available. To prevent it from happening, you may consider using hasNextInt() to check if any more tokens are available.

回答4:

Integer#nextInt throws NoSuchElementException - if input is exhausted

You should check if there is a next line with Integer#hasNextLine

if(sc.hasNextLine()){
    number1=sc.nextInt();
}

回答5:

You must add input.close() at the end...

来源：https://stackoverflow.com/questions/13729294/nosuchelementexception-with-java-util-scanner

标签

java

java.util.scanner