数组为空。无法从while循环中获取信息

debugcn 发表于 Dev

埃利安德

以下代码段应从文本文件中读取，检查文件中有多少个单词，以及有多少行，并支持使用该信息将第n个单词排序到适当的数组中。

 protected static void loadAccountInformationFromFile() throws Exception 
    {
        // These variables control the logic needed to put words in the right array
        int accountNumberCount = 1;
        int firstNameCount = 2;
        int lastNameCount = 3;
        int balanceCount = 4;
        int lastVariableCount = 5;
        int sortCount = 1;


        Scanner account = new Scanner(new File(INPUT_ACCOUNT_FILE)).useDelimiter(",");

        // Using word count to get the nth value later
        int wordCount = 0;
        while(account.hasNext())
        {
            account.next();
            wordCount++;
        }

        // If the count is zero it means the account list is empty
        if (wordCount == 0)
        {
            System.err.println("error: Account list empty."); 
            System.exit(1);
        }

        // Used to test word count feature:
//       System.out.println("Number of words: " + wordCount);

        int lineCount = wordCount / MAX_VALUES_PER_LINE;

        // These arrays will be used to put the account information in the correct place
        // Using the lineCount to create the Array of however large it needs to be
        String[] accountNumber = new String[lineCount - 1];
        String[] firstName = new String[lineCount - 1];
        String[] lastName = new String[lineCount - 1];
        String[] balance = new String[lineCount - 1];
        String[] lastVariable = new String[lineCount - 1];


        // If I don't close and open a new Scanner I get a compiler error       
        account.close();                
        Scanner account2 = new Scanner(new File(INPUT_ACCOUNT_FILE)).useDelimiter(",");

        do
            {

                String[] temp1 = account2.next().split(",");
                String temp2 = "" + temp1;

                if (sortCount == accountNumberCount)
                {
                    accountNumber[sortCount] = temp2;
                }
                if (sortCount == firstNameCount)
                {
                    firstName[sortCount] = temp2;
                }
                if (sortCount == lastNameCount)
                {
                    lastName[sortCount] = temp2;
                }
                if (sortCount == balanceCount)
                {
                    balance[sortCount] = temp2;
                }
                if (sortCount == lastVariableCount)
                {
                    lastVariable[sortCount] = temp2;
                }

                accountNumberCount += 5;
                firstNameCount += 5;
                lastNameCount += 5;
                balanceCount += 5;
                lastVariableCount += 5;

                sortCount++;

                {

                }

            }
        while (account2.hasNext()); 

        // testing to see if it works, but it only returns:
        // [null, [Ljava.lang.String;@55f96302, null, null, null]
        System.out.println(Arrays.toString(accountNumber));

        // This one only returns [Ljava.lang.String;@55f96302
        System.out.println(accountNumber[1]);

        account2.close();
 }

打开文件并正确计算单词数没有问题。但是，如注释文本所示，到了将单词放入适当的数组的时候，这是行不通的。

我的问题是：为什么？而且如何在不使用BufferedWriter / BufferedReader的情况下使其正常工作？

根据一个答案，我纠正了逻辑上的一个缺陷，最终导致

运行：错误：6 Java结果：1建立成功（总时间：0秒）

这是修改后的代码：

 public class Main 
 {
private final static int ACCOUNT_NUMBER_INDEX = 0;
private final static int FIRST_INDEX = 1;
private final static int LAST_INDEX = 2;
private final static int BALANCE_INDEX = 3;
private final static int FREE_CHECKS_INDEX = 4;
private final static int INTEREST_INDEX = 4;
private final static int MAX_VALUES_PER_LINE = 5;
private final static String INPUT_ACCOUNT_FILE = "accountInfo.txt";
protected static String[] fields;

 protected static void loadAccountInformationFromFile() throws Exception 
    {
        // These variables control the logic needed to put words in the right array
        int accountNumberCount = 0;
        int firstNameCount = 1;
        int lastNameCount = 2;
        int balanceCount = 3;
        int lastVariableCount = 4;
        int sortCount = 1;


        Scanner account = new Scanner(new File(INPUT_ACCOUNT_FILE)).useDelimiter(",");

        // Using word count to get the nth value later
        int wordCount = 0;
        while(account.hasNext())
        {
            account.next();
            wordCount++;
        }

        // If the count is zero it means the account list is empty
        if (wordCount == 0)
        {
            System.err.println("error: Account list empty."); 
            System.exit(1);
        }

        // Used to test word count feature:
 //                System.out.println("Number of words: " + wordCount);

        int lineCount = wordCount / MAX_VALUES_PER_LINE;

        // These arrays will be used to put the account information in the correct place
        // Using the lineCount to create the Array of however large it needs to be
        String[] accountNumber = new String[lineCount];
        String[] firstName = new String[lineCount];
        String[] lastName = new String[lineCount];
        String[] balance = new String[lineCount];
        String[] lastVariable = new String[lineCount];


        // If I don't close and open a new Scanner I get a compiler error       
        account.close();                
        Scanner account2 = new Scanner(new File(INPUT_ACCOUNT_FILE)).useDelimiter(",");

        do
            {

                String[] temp1 = account2.next().split(",");
                String temp2 = "" + temp1;

                if (sortCount == accountNumberCount)
                {
                    accountNumber[sortCount] = temp2;
                    accountNumberCount += MAX_VALUES_PER_LINE;
                }
                if (sortCount == firstNameCount)
                {
                    firstName[sortCount] = temp2;
                    firstNameCount += MAX_VALUES_PER_LINE;
                }
                if (sortCount == lastNameCount)
                {
                    lastName[sortCount] = temp2;
                    lastNameCount += MAX_VALUES_PER_LINE;
                }
                if (sortCount == balanceCount)
                {
                    balance[sortCount] = temp2;
                    balanceCount += MAX_VALUES_PER_LINE;
                }
                if (sortCount == lastVariableCount)
                {
                    lastVariable[sortCount] = temp2;
                    lastVariableCount += MAX_VALUES_PER_LINE;
                }

                sortCount++;

            }
        while (account2.hasNext()); 

        // testing to see if it works, but it only returns:
        // [null, [Ljava.lang.String;@55f96302, null, null, null]
        System.out.println(Arrays.toString(accountNumber));

        // This one only returns [Ljava.lang.String;@55f96302
        System.out.println(accountNumber[1]);

        account2.close();

t0mppa

发生这种情况是因为在循环的每次迭代中，您都增加了所有的计数变量。

第一次进入循环时，您具有以下变量：

accountNumberCount == 1
firstNameCount == 2
lastNameCount == 3
balanceCount == 4
lastVariableCount == 5
sortCount == 1

因此sortCount == accountNumberCount，这意味着您将单词放入accountNumber数组的第二个位置（数组的索引从0开始）。

然后增加上述所有变量，进入第二轮，出现以下情况：

accountNumberCount == 6
firstNameCount == 7
lastNameCount == 8
balanceCount == 9
lastVariableCount == 10
sortCount == 2

因此，在第二次迭代中sortCount不再等于任何其他变量。在进一步的迭代中也会发生同样的事情，最终您只能在五个数组之一中插入一个单词。

如果您想完成这项工作，我建议ArrayLists您使用（这样就不必担心数组索引或数组大小）而不是数组，并且每次迭代仅更改一个变量。

private static final int ACCOUNT_NUMBER_COUNT = 1;
private static final int FIRST_NAME_COUNT = 2;
private static final int LAST_NAME_COUNT = 3;
private static final int BALANCE_COUNT = 4;
private static final int LAST_VARIABLE_COUNT = 5;    

List<String> accountNumbers = new ArrayList<String>();
List<String> firstNames = new ArrayList<String>();
List<String> lastNames = new ArrayList<String>();
List<String> balances = new ArrayList<String>();
List<String> lastVariables = new ArrayList<String>();

int sortCount = 1;

// Other things...

do {
    if (sortCount == ACCOUNT_NUMBER_COUNT) {
        accountNumbers.add(temp2);
    } else if (sortCount == FIRST_NAME_COUNT) {
        firstNames.add(temp2);
    } else if (sortCount == LAST_NAME_COUNT) {
        lastNames.add(temp2);
    } else if (sortCount == BALANCE_COUNT) {
        balances.add(temp2);
    } else if (sortCount == LAST_VARIABLE_COUNT) {
        lastVariables.add(temp2);
    }

    if (sortCount < 5) {
        sortCount++;
    } else {
        sortCount = 1;
    }
} while (account2.hasNext());

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