Scanner NoSuchElementException when calling .next(

问题:

In Java, I'm getting this Exception:

Exception in thread "main" java.util.NoSuchElementException
    at java.util.Scanner.throwFor(Unknown Source)
    at java.util.Scanner.next(Unknown Source)
    at com.reading.text.Activity3.readFile(Activity3.java:22)
    at com.reading.text.Activity3.main(Activity3.java:10)

From this Java code:

public static void main(String args[])
{
    readFile("C:/Users/forsakendoll/Desktop/boom.txt");
}

public static void readFile(String path) {
    Scanner file = null;
    try {
        file = new Scanner(new File (path));
    } catch (FileNotFoundException e) {
        e.printStackTrace();
    } finally {
        while (file.hasNext()) {
            for(int counter = 0 ; counter < file.next().length(); counter ++) {
                System.out.println(file.next().charAt(counter));    
            }
        }
    }
}

The Exception is thrown on

System.out.println(file.next().charAt(counter));

What does the Exception mean?

回答1:

You are calling .next() twice on every iteration of the loop, so when you are near the end, you jump off the end of the list and the compilter tells you there is nothing there.

Instead of this:

for(int counter = 0 ; counter < file.next().length(); counter ++) {
    System.out.println(`file.next()`.charAt(counter));    
}

Do this instead:

String temp = file.next();
for(int counter = 0 ; counter < next.length(); counter ++) {
    System.out.println(temp .charAt(counter));    
}  

SEE HERE

回答2:

Don't call next() so much times! It actually go to the next element when you call it. If you need to use it more than once, put it inside a variable and use it.

        String next = file.next();
        for(int counter = 0 ; counter < next.length(); counter ++) {
            System.out.println(next.charAt(counter));    
        }

回答3:

The Scanner.next() method will move the internal iterator along one. Your code should be:

public static void readFile(String path) {
    Scanner file = null;
    try {
        file = new Scanner(new File (path));
    } catch (FileNotFoundException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    } finally {
        while (file.hasNext()) {
            String next = file.next();
            for(int counter = 0 ; counter < next.length(); counter ++) {
                System.out.println(next.charAt(counter));    
            }
        }
    }
}