java - 需要 : array or java. lang.Iterable

Question

我是 Java 的初学者。我只想计算文本文件中每个单词的出现次数。输入格式就像:

A B
A C
C A
B C

这是我到目前为止所做的:

public static void main (String[] args) throws FileNotFoundException
{
    Scanner inputFile = new Scanner(new File("test.txt"));
    while (inputFile.hasNextLine()) {
        String line = inputFile.nextLine();
        System.out.println(line);
        // above is the first part, to read the file in
        // below is the second part, try to count
        Map<String, Integer> counts = new HashMap<>();
        for (String word : line) {
            Integer count = counts.get(word);
            counts.put(word, count == null ? 1 : count + 1);
        }
        System.out.println(counts);
    }
}

预期结果如下:

A 3
B 2
C 3

我在谷歌上找到了第一部分和第二部分，但不知道如何将它们结合起来。任何建议都会有所帮助。

Answer 1

您不能使用 for-each 循环遍历 String(变量 line)。您需要先将其拆分为如下单词:

   String[] words = line.split(" ");
   for(String word : words) {
    // do something
   }

代码中似乎也有错误。用于管理计数的 Map 需要出现在 while 循环之外，否则计数将是特定行的本地计数。更改代码如下:

public static void main (String[] args) throws FileNotFoundException
{
 Scanner inputFile = new Scanner(new File("test.txt"));
 Map<String, Integer> counts = new HashMap<>();
 while (inputFile.hasNextLine()) {
    String line = inputFile.nextLine();
    System.out.println(line);
    // above is the first part, to read the file in
    // below is the second part, try to count

    String[] words = line.split(" ");
    for (String word : words) {
        Integer count = counts.get(word);
        counts.put(word, count == null ? 1 : count + 1);
    }

  } // end of while

  System.out.println(counts);
}