java - 如何编写递归方法来返回包含 token 字符串的文件中的所有行

Question

我的教授给我们布置了一项作业，要求我们编写一个可以执行很多操作的程序。该程序具体执行的一件事是遍历 .txt 文件，并返回您指定的单词的所有实例以及它们所在的行。例如，如果这是文本文件:

This is a test.
Testing the word file.
This will be considered a test.

运行该方法并搜索单词“test”后，您应该收到类似以下内容:

1: This is a test.       
3: This will be considered a test.

现在这是我的问题。他希望我们用递归方法来做，但我不知道如何启动该方法。我知道对于递归方法，您必须调用自身并在每次调用它时进行归约，但是，该方法的参数是一个单词。假设我有:

String getTheWord (String word) {     
    if (word == 0){    //which still wouldn't compile, so I think I should use word == null     
        // something    
    }

    //something smart here      

    return getTheWord(word - 1); // which wouldn't compile
}

那么我该怎么写呢？我认为我必须使用字符串作为参数，否则我怎么知道我要查找的单词是什么？或者也许我错了，任何事情都有帮助!

Answer 1

尝试如下:

public String getTheWord(String textToSearch, String searchingFor,
  int currentLineNumber) {

    // Separate the text into lines.
    String[] lines = textToSearch.split('\n');

    // Get the first line of the (remaining) text.
    String firstLine = lines[0];

    // We're going to have some result from this method call: either
    // an empty string or a message indicating that we found the word.
    String resultFromThisLine = "";        

    // Now, look for the word.
    if (firstLine.contains(searchingFor)) {
        // We found it.
        resultFromThisLine = currentLineNumber + ": " + firstLine + "\n";
    }

    // Now we check to see if there are any lines left.
    if (lines.length == 1) {
        // This was the last line.
        return resultFromThisLine;
    } else {
        // There are more line(s).
        // Create a string with all lines but the first one.
        String remainingLines = "";
        for (int i=1; i<lines.length; i++) {
            remainingLines += lines[i] + "\n";
        }


        // Here's the key part.
        // Take the result from this line, add it to the result from the
        // next line, and return *that*.

        return resultFromThisLine + getTheWord(remainingLines, searchingFor,
          currentLine + 1);

     }
}