ArrayList內容超出范圍，并在Java中的While回圈后被洗掉

我正在嘗試使用 while 回圈將串列串列保存到 ArrayList 中，該回圈遍歷掃描儀中的行。掃描儀正在讀取一個 12 行的二進制文本檔案。串列串列 (ArrayList) 已成功創建，但當 while 回圈終止時，變數 ArrayList 為空并回傳一個空串列串列。我還通過在宣告串列串列的同時宣告一個計數器來測驗代碼，并且計數器在 while 回圈中遞增并在回圈后保留資料。

我對編碼還是很陌生！先感謝您。

public static void main(String[] args) throws Exception{
        
        
        try { 
            readFile();
            data = dataPrep();
        }
        catch (Exception e) {
            e.printStackTrace ();
        }
        
    }
    
    public static void readFile() throws FileNotFoundException {
 
        try {
            File inputtxt = new File("test.txt");
            scanner = new Scanner(inputtxt);
        }
    
        catch (FileNotFoundException error) {
            System.out.println(error);
        }
    }



public static ArrayList<ArrayList> dataPrep(){
        ArrayList<ArrayList> allBinaryNumbers = new ArrayList<ArrayList>();
        ArrayList<Integer> singleBinaryNumber = new ArrayList<Integer>();  
        
        int counter = 0;
      
        while (scanner.hasNextLine()) {
            String line = scanner.nextLine();
            char[] charLine = line.toCharArray();
            
            for (char numb : charLine){
                singleBinaryNumber.add(Integer.parseInt(String.valueOf(numb)));
            }
            allBinaryNumbers.add(singleBinaryNumber);
            System.out.println(allBinaryNumbers); 
            singleBinaryNumber.clear();     
            counter  ;
        }
        
        System.out.println(allBinaryNumbers);
        System.out.println(counter);
        return allBinaryNumbers;
        
    }

我的 test.txt 是這個

00100
11110
10110
10111
10101
01111
00111
11100
10000
11001
00010
01010

uj5u.com熱心網友回復：

您正在重復使用singleBinaryNumber完成填充后清除的相同內容。請記住，這是一個參考（指標），這意味著您在每次迭代中添加相同的串列而不是新串列。

你的代碼應該是這樣的：

public static ArrayList<ArrayList> dataPrep(){
        ArrayList<ArrayList> allBinaryNumbers = new ArrayList<ArrayList>();
        
        int counter = 0;
      
        while (scanner.hasNextLine()) {
            String line = scanner.nextLine();
            char[] charLine = line.toCharArray();
            
            ArrayList<Integer> singleBinaryNumber = new ArrayList<Integer>(); // create a new list for each iteration 
            for (char numb : charLine){
                singleBinaryNumber.add(Integer.parseInt(String.valueOf(numb)));
            }
            allBinaryNumbers.add(singleBinaryNumber);
            System.out.println(allBinaryNumbers); 
            // singleBinaryNumber.clear(); <-- remove this line
            counter  ;
        }
        
        System.out.println(allBinaryNumbers);
        System.out.println(counter);
        return allBinaryNumbers;
        
    }

uj5u.com熱心網友回復：

我認為更好的方法是讓readFile()方法完全做到這一點，讀取檔案而不是僅僅打開它，并讓這個方法回傳一個 ArrayList。它還應該接受一個字串引數，該引數將是檔案路徑（帶有檔案名），而不是直接在方法本身中對檔案路徑進行硬編碼，例如：

// Class instance member variable with Getter & Setter methods.
private String sourceFile; 

// In your main() method:  
// List of Lists. Each internal list is from a different file.
List<List<String>> filesBinaries = new ArrayList<>(); 

// List for current file to be read.
List<String> binaries = readFile(sourceFile);

// Add the current file List object to the 
// List of Lists (filesBinaries).
if (!binaries.isEmpty()) { 
    filesBinaries.add(binaries);
}

有了這個，你的readFile()方法可能看起來像這樣：

public static List<String> readFile(String filePath) throws FileNotFoundException {
    File file = new File(filePath);
    if (!file.exists()) {
        throw new FileNotFoundException("readFile() Method Error! The "
                  "supplied file in the path shown below does not exist!"   System.lineSeparator()
                  file.getAbsolutePath()   System.lineSeparator());
    }

    List<String> binaryLines = new ArrayList<>();
    // 'Try With Resources' is used here to auto-close the reader.
    try (Scanner reader = new Scanner(file)) {
        String line = "";
        while (reader.hasNextLine()) {
            line = reader.nextLine().trim();
            // Data Line Validation:
            /* Skip past blank lines (if any) and any lines
            that do not contain a valid binary string. Valid
            lines would be: 100100  or  00100 11100 01110      */
            if (line.isEmpty() || !line.matches("[01 ] ")) {
                continue;
            }
            binaryLines.add(line);
        }
    }
    return binaryLines;
}

要觸發此方法，您的main()方法可能如下所示：

public static void main(String[] args) {
    List<List<String>> filesData = new ArrayList<>();
    String sourceFile = "BinaryData.txt";  // The CURRENT file to read

    try {
        // Read the desired file...
        List<String> binaryData = readFile(sourceFile);
        // If the binaryData list is not empty then add it to the fileData List.
        if (!binaryData.isEmpty()) {
            filesData.add(binaryData);
        }
    }
    catch (FileNotFoundException ex) {
        System.err.println("The file: \""   sourceFile   "\" could not be "
                  "found!"   System.lineSeparator()   ex.getMessage());
    }
    
    // Display the contens of the filesData List...
    for (int i = 0; i < filesData.size(); i  ) {
         System.out.println("File #"   (i   1)   " Binary Data:");
         System.out.println("====================");
         for (String binaryString : filesData.get(i)) {
             System.out.println(binaryString);
         }
    }
}

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