Scanner throws java.util.NoSuchElementException while reading the input

While reading the input using Scanner, I stuck with below error.

Exception in thread "main" java.util.NoSuchElementException
	at java.util.Scanner.throwFor(Scanner.java:862)
	at java.util.Scanner.next(Scanner.java:1485)
	at java.util.Scanner.nextInt(Scanner.java:2117)
	at java.util.Scanner.nextInt(Scanner.java:2076)
	at com.sample.app.ScannerDemo.main(ScannerDemo.java:11)

 

My code snippet looks like below.

 

ScannerDemo.java

package com.sample.app;

import java.util.Scanner;

public class ScannerDemo {

	public static void main(String[] args) {
		while (true) {
			try (Scanner scanner = new Scanner(System.in)) {
				System.out.println("Enter a number");
				int userInput = scanner.nextInt();
				System.out.println("User entered : " + userInput);

				System.out.println("Enter non zero to continue and 0 to exit");

				userInput = scanner.nextInt();
				if (0 == userInput) {
					System.exit(0);
				}

			}
		}

	}

}

 

Sample Output

Enter a number
123
User entered : 123
Enter non zero to continue and 0 to exit
1
Enter a number
Exception in thread "main" java.util.NoSuchElementException
	at java.util.Scanner.throwFor(Scanner.java:862)
	at java.util.Scanner.next(Scanner.java:1485)
	at java.util.Scanner.nextInt(Scanner.java:2117)
	at java.util.Scanner.nextInt(Scanner.java:2076)
	at com.sample.app.ScannerDemo.main(ScannerDemo.java:11)

 

Root cause

After some analysis, I figured out there is a problem in using try-with-resource statement. try-with-resource statement close the scanner instance automatically when the scanner went out of scope. When the scanner#close is initiated, it internally close the System.in input stream as well.

 

I verified the same using below statement.

System.out.println("Is the input stream available ?" + System.in.available());

ScannerDemo.java

package com.sample.app;

import java.io.IOException;
import java.util.Scanner;

public class ScannerDemo {

	public static void main(String[] args) throws IOException {
		while (true) {
			try (Scanner scanner = new Scanner(System.in)) {
				System.out.println("Is the input stream available ?" + System.in.available());

				System.out.println("Enter a number");
				int userInput = scanner.nextInt();
				System.out.println("User entered : " + userInput);

				System.out.println("Enter non zero to continue and 0 to exit");

				userInput = scanner.nextInt();
				if (0 == userInput) {
					System.exit(0);
				}

			}

			System.out.println("Is the input stream available ?" + System.in.available());
		}

	}

}

Sample Output

Is the input stream available ?0
Enter a number
123
User entered : 123
Enter non zero to continue and 0 to exit
1
Exception in thread "main" java.io.IOException: Stream closed
	at java.io.BufferedInputStream.getInIfOpen(BufferedInputStream.java:159)
	at java.io.BufferedInputStream.available(BufferedInputStream.java:410)
	at com.sample.app.ScannerDemo.main(ScannerDemo.java:26)

How I resolved the problem?

Do not close the Scanner, as long as you need to work with it.

 

ScannerDemo.java

package com.sample.app;

import java.io.IOException;
import java.util.Scanner;

public class ScannerDemo {

	public static void main(String[] args) throws IOException {
		try (Scanner scanner = new Scanner(System.in)) {
			while (true) {

				System.out.println("Enter a number");
				int userInput = scanner.nextInt();
				System.out.println("User entered : " + userInput);

				System.out.println("Enter non zero to continue and 0 to exit");

				userInput = scanner.nextInt();
				if (0 == userInput) {
					System.exit(0);
				}

			}

		}

	}

}

Sample Output

Enter a number
123
User entered : 123
Enter non zero to continue and 0 to exit
1
Enter a number
124
User entered : 124
Enter non zero to continue and 0 to exit
1
Enter a number
125
User entered : 125
Enter non zero to continue and 0 to exit
0

 

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