BufferedReader似乎只讀取文件的最后一行

Question

我正在嘗試編寫一個方法來獲取多行制表符分隔文件並將該文件的內容作為String數組的arraylist返回（每行是一個String []，每個這樣的String []是一個arraylist的元素）。 我的問題是，我無法判斷輸出是否正確。 我已經打印了每個arraylist元素和String []元素，因為它們被保存到arraylist，並且這些打印看起來是正確的。 但是在返回arraylist並在其中打印String []后，它們似乎只包含文件最后一行的內容。 我懷疑它可能是我不知道的FileReader或BufferedReader。 Anyhoo，這是代碼：

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;
    }
}

輸入文件是：

1   2
3   4
5   6

輸出是：

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.

謝謝你！

Answer 1

你只是建立一個單一的字符串數組和重用，對所有線路。 因此，您的ArrayList只包含對同一對象的多個引用。 當你調用arrayListOfStringArrays.add(productString);時，你需要了解它arrayListOfStringArrays.add(productString); 那不是將數組的副本添加到ArrayList - 它只是添加一個引用 。 （ productString的值只是一個引用，而不是數組本身。）

移動這個：

String[] productString = new String[noOfTokens];

進入while循環，一切都應該很好。 （無論如何，你應該在finally塊中關閉文件句柄。）

Answer 2

這對我來說似乎有太多代碼需要處理。 試試這個改變的fileToStringArray方法。

public static ArrayList<String[]> fileToStringArray(File file) throws FileNotFoundException, IOException {
    ArrayList<String[]> returnVal = new ArrayList<String[]>();
    // Scanner is a nifty utility for reading Files
    Scanner fIn = new Scanner(file);
    // keep reading while the Scanner has lines to process
    while (fIn.hasNextLine()) {
        // take the next line of the file, and split it up by each tab
        // and add that String[] to the list
        returnVal.add(fIn.nextLine().split("\t", -1));
    }
    return returnVal;
}