java - BufferedReader 似乎只读取文件的最后一行

Question

我正在尝试编写一个方法来获取一个多行制表符分隔的文件，并将该文件的内容作为字符串数组的数组列表返回(每一行都是一个字符串[]，每个这样的字符串[]都是一个元素一个数组列表)。我的问题是，我无法判断输出是否正确。我打印了每个 arraylist 元素和 String[] 元素，因为它们被保存到 arraylist，这些打印看起来是正确的。但是在返回 arraylist 并在其中打印 String[] 之后，它们似乎只有文件最后一行的内容。我怀疑它可能与我不知道的 FileReader 或 BufferedReader 有关。 Anyhoo，这是代码:

public class DataParsingTest {

    static File AAPLDailyFile = new File("./textFilesForMethodTests/dataParsingPractice2.tsv");

    public static void main(String[] args) throws FileNotFoundException, IOException {
        ArrayList<String[]> stringArrayList = fileToStringArray(AAPLDailyFile);
        System.out.println("stringArray.size() = " + stringArrayList.size());
        System.out.println(stringArrayList.get(0)[0]);

        for (int i = 0; i < stringArrayList.size(); i++) {
            for (int j = 0; j < stringArrayList.get(i).length; j++) {
                System.out.println("index of arraylist is " + i + " and element at index " + j + " of that array is " + stringArrayList.get(i)[j]);
            }
        }
    }

    public static ArrayList<String[]> fileToStringArray(File file) throws FileNotFoundException, IOException {
        ArrayList<String[]> arrayListOfStringArrays = new ArrayList<String[]>();
        FileReader fileReader = new FileReader(file);
        BufferedReader bufferedReader = new BufferedReader(fileReader);
        int nextChar = 0;
        int noOfTokens = 1; // because the first token doesn't have a tab or newline before it
        int startIndex = 0, endIndex = 0, tokenIndex = 0;
        String toRead = "";
        toRead = bufferedReader.readLine();
        for (int i = 0; i < toRead.length(); i++) {
            if (toRead.charAt(i) == '\t') {
                noOfTokens++;
            }
        }
        System.out.println("noOfTokens = " + noOfTokens);
        bufferedReader.close();
        fileReader.close();
        String[] productString = new String[noOfTokens];
        startIndex = 0;
        endIndex = 0;
        tokenIndex = 0;
        FileReader fileReader2 = new FileReader(file);
        BufferedReader bufferedReader2 = new BufferedReader(fileReader2);

        tokenIndex = 0;
        int count = 1;
        while ((toRead = bufferedReader2.readLine()) != null) { 
            System.out.println("toRead = " + toRead);
            startIndex = -1; // [L - so that the first time an array element is assigned, it's upped to 0]
            endIndex = 0;
            tokenIndex = 0;
            while (true) {  
                endIndex = toRead.indexOf("\t", startIndex + 1);  
                if (endIndex == -1) {
                    productString[tokenIndex] = toRead.substring(startIndex + 1);
                    System.out.println("tokenIndex = " + tokenIndex);
                    System.out.println("productString[" + tokenIndex + "] = " + productString[tokenIndex]);
                    tokenIndex++;
                    count++;
                    arrayListOfStringArrays.add(productString);
                    System.out.println("just added an array to the list. the first element is " + productString[0]);
                    break;
                }
                productString[tokenIndex] = toRead.substring(startIndex + 1, endIndex);
                System.out.println("tokenIndex = " + tokenIndex);
                System.out.println("productString[" + tokenIndex + "] = " + productString[tokenIndex]);
                startIndex = endIndex;
                tokenIndex++;
                count++;
            }
        }
        fileReader2.close();
        bufferedReader2.close();
        return arrayListOfStringArrays;
    }
}

输入文件是:

1   2
3   4
5   6

输出是:

noOfTokens = 2
toRead = 1        2
tokenIndex = 0
productString[0] = 1
tokenIndex = 1
productString[1] = 2
just added an array to the list. the first element is 1
toRead = 3        4
tokenIndex = 0
productString[0] = 3
tokenIndex = 1
productString[1] = 4
just added an array to the list. the first element is 3
toRead = 5        6
tokenIndex = 0
productString[0] = 5
tokenIndex = 1
productString[1] = 6
just added an array to the list. the first element is 5
stringArray.size() = 3
5 // from here on up, it looks like the method works correctly
index of arraylist is 0 and element at index 0 of that array is 5
index of arraylist is 0 and element at index 1 of that array is 6
index of arraylist is 1 and element at index 0 of that array is 5
index of arraylist is 1 and element at index 1 of that array is 6
index of arraylist is 2 and element at index 0 of that array is 5
index of arraylist is 2 and element at index 1 of that array is 6 //these 6 lines only reflect the last line of the input file.

非常感谢!

Answer 1

您只是创建了一个单个 字符串数组，并将其重复用于所有行。所以您的 ArrayList 只包含对同一对象的多个引用。您需要了解，当您调用 arrayListOfStringArrays.add(productString); 时，并不是将数组的副本添加到 ArrayList - 它只是添加一个 reference。 (productString 的值只是一个引用，而不是数组本身。)

只需移动这个:

String[] productString = new String[noOfTokens];

进入 while 循环，一切都应该顺利。 (无论如何，在这方面。您还应该在 finally block 中关闭文件句柄。)