Java InputMismatchException error. What causes it?

Question

What is the reason why that the following Java procedure causes a InputMismatchException error?

import java.util.Scanner;
public class Main {
    public static void main(String[] args) {
        String input = "hello 12345\n";
        Scanner s = new Scanner(input);
        s.next("hello ");
    }
}

Thank you

Answer 1

This is occurring because hello[space] is not a token in the String. The String is being tokenized by a whitespace delimiter so the tokens are as follows:

String input = "hello 12345\n";
Scanner s = new Scanner(input);

while(s.hasNext()){
    System.out.println(s.next());
}
//Outputs: Hello
//         12345

The error message is simply telling you that it cannot find hello[space] amongst the tokens, which are hello and 12345.

If you want to find the pattern regardless of delimiters use, String#findInLine:

s.findInLine("hello ");