java - 循环结束后扫描仪读取

Question

Scanner.hasNext 读取是否有 token ，当没有 token 时，它应该结束循环，但是出现错误，没有找到这样的元素异常，但是当我切换第 1 行和第 2 行时，我工作得很好。

    public class ScannerDemo {

    public static void main(String[] args) {

        String s = "Hello World! 3 + 3.0 = 6.0 true ";
        Long l = 13964599874l;
        s = s + l;

        // create a new scanner with the specified String Object
        Scanner scanner = new Scanner(s);

        // find the next long token and print it
        // loop for the whole scanner
        while (scanner.hasNext()) {

            // if the next is a long, print found and the long
            // LINE 1
            if (scanner.hasNextLong()) {
                System.out.println("Found :" + scanner.nextLong());
            }
            // if no long is found, print "Not Found:" and the token
            // LINE 2
            System.out.println("Not Found :" + scanner.next());

        }
    }
}

错误

Not Found :Hello
Not Found :World!
Found :3
Not Found :+
Not Found :3.0
Not Found :=
Not Found :6.0
Not Found :true
Found :13964599874
Exception in thread "main" java.util.NoSuchElementException
    at java.util.Scanner.throwFor(Unknown Source)
    at java.util.Scanner.next(Unknown Source)
    at ScannerDemo.main(ScannerDemo.java:23)

Answer 1

那是因为你没有停止循环。读取Long后，它将继续: System.out.println("未找到:"+ Scanner.next());

通过在 System.out.println("Found :"+ Scanner.nextLong()); 之后添加 continue 来修复此问题

        if (scanner.hasNextLong()) {
            System.out.println("Found :" + scanner.nextLong());
            continue;
        }