Java初学者: Message coming up under General output in java although process was completed

Question

我写了一个程序来显示猜出 jar 里弹珠数量最接近的人的 ID 号。这是程序:

import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;
import java.io.PrintWriter;
import java.util.Scanner;

public class SuperMarbles
{
  public static void main(String[] args) throws IOException
  {
    int guess = 0;
    int contestants = 0;
    int num_marbles, answer, id, winner = 0;

    Scanner scanner = new Scanner(new FileReader("promo.txt"));
    PrintWriter printWriter = new PrintWriter(new FileWriter("winner.txt"));

    num_marbles = scanner.nextInt();
    id = scanner.nextInt();
    while (id != 0)
    {
      answer = scanner.nextInt();
      if (answer > guess && answer <= num_marbles)
      {
        guess = answer;
        winner = id;
        id = scanner.nextInt();
        contestants++;
      }
    }

    if (guess == 0)
    {
      printWriter.printf("There are %d contestants", contestants);
      printWriter.printf("\nThere are no winners");
    }
    else
    {
      printWriter.printf("There are %d contestants", contestants);
      printWriter.printf("\nThe winner is ID#%d", winner);
    }
    scanner.close();
    printWriter.close();

  }

}

这是输入文件“promo.txt”中的数据:
258
0001 200
0002 198
0003 430
0004 12
0005 30
0006 45
0007 154
0008 250
0009 120
0

现在，我使用 JCreator，当我尝试编译时，在“构建输出”下，我没有收到任何错误并且“进程已完成”，但在“常规输出”下，这就是我得到的:

Exception in thread "main" java.util.NoSuchElementException
at java.util.Scanner.throwFor(Scanner.java:907)
at java.util.Scanner.next(Scanner.java:1530)
at java.util.Scanner.nextInt(Scanner.java:2160)
at java.util.Scanner.nextInt(Scanner.java:2119)
at SuperMarbles.main(SuperMarbles.java:25)

Process completed.

此外，未创建输出文件“winner.txt”。对于 java，我是个新手，但任何帮助将不胜感激。

Answer 1

我已在您的代码中添加了一些调试功能。看看它向我们展示了什么:

...

num_marbles = in.nextInt();
System.out.println("num_marbles=" + num_marbles);
id = in.nextInt();
System.out.println("id=" + id);
while (id!=0) {
    answer = in.nextInt();
    System.out.println("answer=" + answer);

...

输出:

[C:\java_code\]java SuperMarbles
num_marbles=258
id=1
answer=200
answer=198
answer=3
answer=430
answer=4
answer=12
answer=5
answer=30
answer=6
answer=45
answer=7
answer=154
answer=8
answer=250
answer=120
answer=0
Exception in thread "main" java.util.NoSuchElementException
    at java.util.Scanner.throwFor(Unknown Source)
    at java.util.Scanner.next(Unknown Source)
    at java.util.Scanner.nextInt(Unknown Source)
    at java.util.Scanner.nextInt(Unknown Source)
    at SuperMarbles.main(SuperMarbles.java:16)

您已正确获取所有输入，但即使没有更多输入，您仍不断尝试获取它。

当in.hasNext()为false时，您需要停止。但您根本没有对此进行测试。

此外，如果将最后的调试输出更改为

System.out.println("answer=" + answer + ", id=" + id);

你会发现id永远不等于0，因此你的while循环永远不会结束。

可能还有其他问题，但这是两个很好的开始。祝你好运!