是否可以在 for 或 while 循环中声明引用变量？

Question

我编写了一个简短的代码，从名为“ChosenCompanies”的类中声明了 6 个引用变量，以练习 Java 中的类和构造函数。

如下：

public static void main(String[] args) {

    String[] FinalCompaniesName = new String[6];

    ChosenCompanies com1 = new ChosenCompanies();
    ChosenCompanies com2 = new ChosenCompanies();
    ChosenCompanies com3 = new ChosenCompanies();
    ChosenCompanies com4 = new ChosenCompanies();
    ChosenCompanies com5 = new ChosenCompanies();
    ChosenCompanies com6 = new ChosenCompanies();

    Scanner scanner = new Scanner(System.in);
    int choice;
    int count = 1;
    while(count <= 2) {
        switch(count) {
        case 1:
            System.out.println("Choose one:");
            System.out.println("1. " + com1.name);
            System.out.println("2. " + com2.name);
            System.out.println("3. " + com3.name);
            choice = scanner.nextInt();
            switch(choice) {
            case 1:
                FinalCompaniesName[0] = com1.name;
                break;
            case 2:
                FinalCompaniesName[0] = com2.name;
                break;
            case 3:
                FinalCompaniesName[0] = com3.name;
                break;
            }
        break;
        case 2:
            System.out.println("Choose one:");
            System.out.println("1. " + com4.name);
            System.out.println("2. " + com5.name);
            System.out.println("3. " + com6.name);
            choice = scanner.nextInt();
            switch(choice) {
            case 1:
                FinalCompaniesName[1] = com4.name;
                break;
            case 2:
                FinalCompaniesName[1] = com5.name;
                break;
            case 3:
                FinalCompaniesName[1] = com6.name;
                break;
            }
            break;
        }    
        count++;
    }
        System.out.println("You have chosen: "
 + FinalCompaniesName[0] + ", " + FinalCompaniesName[1]);

}

从上面的代码可以看出，这两部分除了引用变量的名字（com1, com2, com3, com4...）之外几乎是一样的：

第 1 部分：

        switch(count) {
        case 1:
            System.out.println("Choose one:");
            System.out.println("1. " + com1.name);
            System.out.println("2. " + com2.name);
            System.out.println("3. " + com3.name);
            choice = scanner.nextInt();
            switch(choice) {
            case 1:
                FinalCompaniesName[0] = com1.name;
                break;
            case 2:
                FinalCompaniesName[0] = com2.name;
                break;
            case 3:
                FinalCompaniesName[0] = com3.name;
                break;
            }
         break;

第 2 部分：

        case 2:
            System.out.println("Choose one:");
            System.out.println("1. " + com4.name);
            System.out.println("2. " + com5.name);
            System.out.println("3. " + com6.name);
            choice = scanner.nextInt();
            switch(choice) {
            case 1:
                FinalCompaniesName[1] = com4.name;
                break;
            case 2:
                FinalCompaniesName[1] = com5.name;
                break;
            case 3:
                FinalCompaniesName[1] = com6.name;
                break;
                }
            break;
        }    

我想知道是否可以通过使用 for 或 while 循环来最小化上述代码的数量，因为引用变量的名称会增加 1，就像常见 for 语句中的整数“i”一样。

简而言之，是否可以通过循环来声明引用变量？

Answer 1

您的示例令人困惑，因此我不知道您到底想完成什么，但这里有一个示例，说明如何提示用户从现有公司名称列表中为每个公司选择一个新名称：

    public class Company {

    /**
     * Array of available company names used to construct
     * initial companies. These names are also used as possible
     * choices when changing company names through {@link #changeCompanyNames()}
     */
    private static final String[] COMPANY_NAMES = new String[]
            { "Alphabet", "Microsoft", "IBM", "Amazon", "Oracle", "Apple" };

    /**
     * <p>
     * Array of Company objects initialized with a fixed number of
     * new companies equal to the number of String entries in {@link #COMPANY_NAMES}.
     * </p><p>
     * Each company entry will inheriting a name from the mentioned array
     * in the initialization process done in {@link #initializeCompanies()}
     * </p>
     */
    public static final Company[] COMPANIES = initializeCompanies();

    private String name;

    /**
     * Internal constructor with private access to
     * prevent class construction outside this class
     */
    private Company(String name) {
        this.name = name;
    }

    /**
     * Should only be used internally on class loading to
     * construct an array of companies from a list of company names.
     */
    private static Company[] initializeCompanies() {

        Company[] companies = new Company[COMPANY_NAMES.length];
        for (int i = 0; i < COMPANY_NAMES.length; i++) {
            companies[i] = new Company(COMPANY_NAMES[i]);
        }
        return companies;
    }

    /**
     * Change any or all company names by prompting the user to choose
     * a new name for each company from the list of available companies.
     */
    public static void changeCompanyNames() {

        java.util.Scanner scanner = new java.util.Scanner(System.in);
        /*
         * Create a new array of company names that is identical to the existing
         * array of company names. We will change names here on user input and
         * then update each new company name to values from this array.
         */
        final String[] finalCompanyNames = COMPANY_NAMES.clone();
        /*
         * Iterate through an array of companies with a for-loop
         * accessing and processing each company entry
         */
        for (int i1 = 0; i1 < COMPANIES.length; i1++)
        {
            /* Prompt the user to choose a new company name for the
             * company at index i1 from COMPANIES array.
             */
            System.out.printf("Choose a new company name for %s company:%n", COMPANIES[i1].name);
            /*
             * Again iterate through all companies and print their names to
             * console offering the user a list of possible names to choose from
             */
            for (int i2 = 0; i2 < COMPANIES.length; i2++) {
                System.out.printf("%d. %s%n", i2 + 1, COMPANIES[i2].name);
            }
            /*
             * Get user input and validate it, then either update the array of
             * final names with the new entry or print an error and move the index
             * to the previous position if the input was an invalid number
             */
            int input = scanner.nextInt();
            if (input > 0 && input <= COMPANIES.length) {
                finalCompanyNames[i1] = COMPANY_NAMES[input - 1];
                System.out.println("You have choosen company name " + finalCompanyNames[i1]);
            }
            else {
                System.out.printf("Error: input is not in range (1-%d)%n", COMPANIES.length);
                /*
                 * It's imperative that we move the index to the previous
                 * position so we can iterate over this company entry again
                 */
                i1 -= 1;
            }
        }
        // Print simple line separator
        System.out.println("");

        /* Print each choosen name that is different then the original
         * company name and update the appropriate company name field value
         */
        for (int i = 0; i < finalCompanyNames.length; i++)
        {
            if (!finalCompanyNames[i].equals(COMPANY_NAMES[i])) {
                System.out.printf("Company %s has changed name to %s%n", COMPANY_NAMES[i], finalCompanyNames[i]);
                COMPANIES[i].name = finalCompanyNames[i];
            }
        }
    }
}

用户完成选择后的控制台输出示例：

Company Alphabet has changed name to IBM
Company Microsoft has changed name to Amazon
Company IBM has changed name to Alphabet
Company Amazon has changed name to Oracle
Company Oracle has changed name to Microsoft
Company Apple has changed name to Amazon

在这里，我们可以设置任意数量的公司，并让用户为他们选择任何提供的名称。对于初学者来说，这段代码可能看起来有点令人生畏，但这实际上是最简单的方法，无需涉及任何更复杂的 Java 概念。

请随时询问有关此实施的任何问题。我很乐意提供帮助。

编辑：更新了代码以包含详细的 cmets 和更易于理解的更全面的结构，并修复了索引问题。

Answer 2

在 Java 中无法创建动态变量（但使用反射，请参阅 here）

您可以创建一个数组并使用i 作为索引，如chosenCompanies[i]。

否则您可以使用列表或地图。

编辑：

那将是例如看起来像这样。除了代码的意义，这个例子只展示了如何使用数组：

    String[] choosenCompanieNames = new String[2]; // you only store two values, not 6 values

    //lets store the values to chose in arrays
    String[] possibleCompanieNames = new String[6]; // 6 possible values to choose (com1 - com6)
    possibleCompanieNames[0] = "com1";
    possibleCompanieNames[1] = "com2";
    possibleCompanieNames[2] = "com3";
    possibleCompanieNames[3] = "com4";
    possibleCompanieNames[4] = "com5";
    possibleCompanieNames[5] = "com6";

    //I deleted the while loop, as it only has two ways and every way has its own code. 

    Scanner scanner = new Scanner(System.in);
    int choice;

    System.out.println("Choose one:");
    System.out.println("1. " + possibleCompanieNames[0]);
    System.out.println("2. " + possibleCompanieNames[1]);
    System.out.println("3. " + possibleCompanieNames[2]);
    choice = scanner.nextInt();
    choosenCompanieNames[0] = possibleCompanieNames[choice-1]; //you must subtract one, as the array index starts at 0 and ends on 5

    System.out.println("Choose one:");
    System.out.println("1. " + possibleCompanieNames[3]);
    System.out.println("2. " + possibleCompanieNames[4]);
    System.out.println("3. " + possibleCompanieNames[5]);
    choice = scanner.nextInt();
    choosenCompanieNames[1] = possibleCompanieNames[3+choice-1]; //here you want com4, com5 and com6, so you can e.g. add 3 to index and substract one like code above. Or better add only 2, as 3-1=2


    System.out.println("You have chosen: "
         + choosenCompanieNames[0] + ", " + choosenCompanieNames[1]);