数组未显示（Java）

Question

我的任务有一种方法出现问题。这是此方法的要求：

“此方法使用循环列出阵列中包含的所有帐户，将每个帐户详细信息添加到字符串，然后以下面屏幕截图中指定的格式输出到屏幕。通过检查每个数组插槽是否有一个帐户对象，然后将其详细信息添加到输出String（arrayname [index]！= null），确保没有越界异常“

这是我的代码方法：

public void listAllAccounts() 
{ 
    String allAccountsString = "List of all accounts: \n"; 

    for(int i = 0; i < ACCOUNT_SPACES; i++) 
    { 
     //allAccountsString += accountArray[numAccounts]; 
     if (accountArray[i] !=null) 
     { 
      allAccountsString += accountArray[i].toString() + "\n\n" ; 
     } 
    } 
    JOptionPane.showMessageDialog(null, allAccountsString); 

问题是，消息对话框不显示我已经创建的帐户。它只是显示"List of all accounts: \n";

任何想法？

这是整个类的代码：

public class MyBankController 
{ 
    /** 
    * Variables that will be used by this class 
    */ 

    private BankAccount newAccount; 
    private BankAccount accountArray[]; 
    int numAccounts = 0; 
    int ACCOUNT_SPACES = 2; 
    private boolean accountStatus = false; 

    /** 
    * Constructor for objects of class MyBankController - to be left empty by requirements. 
    */ 
    public MyBankController() 
    { 
     // 
    } 

    /** 
    * A method to create a new account, accepting user input and allocating memory space. 
    */ 
    public void createAccount(String customerName, int accountNumber) 
    { 
     newAccount = new BankAccount(customerName, accountNumber); 
     accountArray = new BankAccount [2]; 
     if(numAccounts +1 <= ACCOUNT_SPACES) 
     { 
      numAccounts++; 
      printAccountDetails(); 
     } 
     else 
     { 
      JOptionPane.showMessageDialog(null, "Sorry, a maximum limit of accounts allowed has been reached." + "\n" + "Limit: " + numAccounts + "/10", "Warning!", JOptionPane.INFORMATION_MESSAGE); 
     } 
    } 

    /** 
    * Method to print the account details - by calling an object from the BankAccount class. 
    */ 

    private void printAccountDetails() 
    { 
     JOptionPane.showMessageDialog(null, newAccount.toString(), "Account Details", JOptionPane.INFORMATION_MESSAGE); 
    } 

    public void listAllAccounts() 
    { 
     String allAccountsString = "List of all accounts: \n"; 

     for(int i = 0; i < ACCOUNT_SPACES; i++) 
     { 
      if (accountArray[i] !=null) 
      { 
       allAccountsString += accountArray[i].toString() + "\n\n" ; 

      } 
      JOptionPane.showMessageDialog(null, allAccountsString); 
     } 
    } 

    public void listAllOpenAccounts() 
    { 

     String allAccountsString = "List of all accounts: \n"; 

     for(int i = 0; i < ACCOUNT_SPACES; i++) 
     { 
      //allAccountsString += accountArray[numAccounts]; 
      if (accountArray[i] !=null && accountStatus == true) 
      { 
       allAccountsString += accountArray[i].toString() + "\n\n" ;`` 
      } 
     } 
     JOptionPane.showMessageDialog(null, allAccountsString); 
    } 
} 

Answer 1

感谢您的帮助。我使用了一个名为newAccount的变量，而不是数组本身。

的解决方案是：

/** 
* Importing JOptionPane for user GUI. 
*/ 
import javax.swing.JOptionPane; 
import javax.swing.*; 
/** 
* The MyBankController class will control the creation of accounts utilizing the BankAccount class you 
created in Part A of the assignment 
* 
* @author Katarzyna Korzeniec 
* @version 03/02/2015 
*/ 
public class MyBankController 
{ 
    /** 
    * Variables that will be used by this class 
    */ 

    //private BankAccount newAccount; 
    private BankAccount accountArray[] = new BankAccount[2]; 
    int numAccounts = 0; 
    int ACCOUNT_SPACES = 2; 
    //boolean accountStatus = false; 

    /** 
    * Constructor for objects of class MyBankController - to be left empty by requirements. 
    */ 
    public MyBankController() 
    { 
     // 
    } 

    /** 
    * A method to create a new account, accepting user input and allocating memory space. 
    */ 
    public void createAccount(String customerName, int accountNumber) 
    { 


     if(numAccounts +1 <= ACCOUNT_SPACES) 
     { 
      accountArray[numAccounts] = new BankAccount(customerName, accountNumber); 

      printAccountDetails(numAccounts); 
      numAccounts++; 
     } 
     else 
     { 
      JOptionPane.showMessageDialog(null, "Sorry, a maximum limit of accounts allowed has been reached." + "\n" + "Limit: " + numAccounts + "/10", "Warning!", JOptionPane.INFORMATION_MESSAGE); 
     } 
    } 

    /** 
    * Method to print the account details - by calling an object from the BankAccount class. 
    */ 

    private void printAccountDetails(int value) 
    { 
     JOptionPane.showMessageDialog(null, accountArray[value].toString(), "Account Details", JOptionPane.INFORMATION_MESSAGE); 
    } 

    public void listAllAccounts() 
    { 
     String allAccountsString = "List of all accounts: \n"; 

     for(int i = 0; i < ACCOUNT_SPACES; i++) 
     { 
      if (accountArray[i] !=null) 
      { 
       allAccountsString += accountArray[i].toString() + "\n\n" ; 

      } 

     } 
     JOptionPane.showMessageDialog(null, allAccountsString); 
    } 

    public void listAllOpenAccounts() 
    { 

     String allAccountsString = "List of all accounts: \n"; 

     for(int i = 0; i < ACCOUNT_SPACES; i++) 
     { 
      //allAccountsString += accountArray[numAccounts]; 
      if (accountArray[i] !=null && (accountArray[i].getAccountStatus() !=false)) 
      { 
       allAccountsString += accountArray[i].toString() + "\n\n" ; 
      } 
     } 
     JOptionPane.showMessageDialog(null, allAccountsString); 
    } 
} 

Answer 2

只是用于测试目的试试这个，看看会发生什么：

public void listAllAccounts() 
{ 
    String allAccountsString = "List of all accounts: \n"; 

    if (accountArray.length == 0) { 
     allAccountsString += "the array is empty, there are no accounts\n"; 
    } 

    for(int i = 0; i < ACCOUNT_SPACES; i++) 
    { 
     //allAccountsString += accountArray[numAccounts]; 
     if (accountArray[i] !=null) 
     { 
      allAccountsString += accountArray[i].toString() + "\n\n" ; 
     } else { 
      allAccountsString += "null value here \n\n" ; 
     } 
    } 
    JOptionPane.showMessageDialog(null, allAccountsString); 

Answer 3

如果你都不放过一个预定义的字符串，有是以下情况需要考虑：

1. ACCOUNT_SPACES可能为0，因此您永远不会进入for循环。 补救措施：运行循环，直到达到数组长度或使用foreach构造;
2. accountArray[i] !=null为false，因此您的数组包含空条目。 补救措施：您的数组必须预填充一些数据。

另外请注意，accountArray[i] !=null不确保ArrayIndexOutOfBoundsException不会被抛出。因此，应该遍历数组，直到array.length - 1元素为此不发生。

最后需要注意的是，Swing组件并不考虑换行符（\n），但它们可以包含一些基本的HTML代码以增强图形输出。因此，将\n替换为<br/>以实现换行似乎是合理的。还请阅读How to Use HTML in Swing Components指南。