java - java文件从文档中间逆序读取

Question

我想在文件中查找关键字。找到关键字后，我想在这个关键字之前得到 50 个单词，在这个关键字之后得到 50 个单词。

我想知道是否有办法以相反的顺序读取文件。

Answer 1

您仍然需要逐行逐字读取文件以找到您要查找的单词...您可以做的是拥有一个包含 50 个单词的缓冲区，例如字符串数组，然后加载您的文本，如果不是您要查找的单词，请将其放入缓冲区中，新单词会覆盖最旧的单词。如果你找到了你需要的东西，从你的缓冲区中取出所有的单词并阅读接下来的 50 个单词。

Answer 2

请使用以下代码。

List<String> previousWords = new ArrayList<String>();
List<String> nextWords = new ArrayList<String>();
boolean foundKeyWord = false;

Scanner sc2 = null;
try {
    sc2 = new Scanner(new File("translate.txt"));
} catch (FileNotFoundException e) {
    e.printStackTrace();  
}
while (sc2.hasNextLine()) {
        Scanner s2 = new Scanner(sc2.nextLine());
    boolean b;
    while (b = s2.hasNext()) {
        String s = s2.next();
        if(!foundKeyWord) {
           if(s.equals(findKeyWord)) {
             foundKeyWord = true;
           }
        }
       //Keyword not found then add to the previouswords list
        if(!foundKeyWord) {
           previousWords.add(s);
        } else {
          //already key found now we need to add next 50 words
           if(nextWords.size <= 50) {
               nextWords.add(s);
           } else {
             //if 50 key words are added then break from the loop, if in case if there are less than 50 words in file after keyword then scanner will end.
             break;
           }

        }

    }
}

//Now we need to fix the previous 50 key words in case if keyword is found after 50th word.

  if(previousWords.size > 50){
     previousWords.subList(previousWords.size() - 50, previousWords.size());
  }