與陣列迭代循環

Question

我只是有我敢肯定是一個非常容易和快速的問題在這裏......所以我們可以說我有一個帳戶類，如下所示：

import java.text.NumberFormat; 

public class Account 
{ 
    private final double RATE = 0.03; // interest rate of 3.5% 
    private long acctNumber; 
    private double balance; 
    private String name; 

    //----------------------------------------------------------------- 
    // Sets up the account by defining its owner, account number, 
    // and initial balance. 
    //----------------------------------------------------------------- 
    public Account (String owner, long account, double initial) 
    { 
     name = owner; 
     acctNumber = account; 
     balance = initial; 
    } 
    //----------------------------------------------------------------- 
    // Deposits the specified amount into the account. Returns the 
    // new balance. 
    //----------------------------------------------------------------- 
    public double deposit (double amount) 
    { 
     balance = balance + amount; 
     return balance; 
    } 
    //----------------------------------------------------------------- 
    // Withdraws the specified amount from the account and applies 
    // the fee. Returns the new balance. 
    //----------------------------------------------------------------- 
    public double withdraw (double amount, double fee) 
    { 
     balance = balance - amount - fee; 
     return balance; 
    } 
    //----------------------------------------------------------------- 
    // Adds interest to the account and returns the new balance. 
    //----------------------------------------------------------------- 
    public double addInterest() 
    { 
     balance += (balance * RATE); 
     return balance; 
    } 
    //----------------------------------------------------------------- 
    // Returns the current balance of the account. 
    //----------------------------------------------------------------- 
    public double getBalance() 
    { 
     return balance; 
    } 
    //----------------------------------------------------------------- 
    // Returns a one-line description of the account as a string. 
    //----------------------------------------------------------------- 
    public String toString() 
    { 
     NumberFormat fmt = NumberFormat.getCurrencyInstance(); 
     return acctNumber + "\t" + name + "\t" + fmt.format(balance); 
    } 
} 

我創建了銀行類這裏顯示...

public class Bank 
{ 
    Account[] accounts;// = new Account[30]; 
    int count=0; 
    String name; 

    public Bank(String name) 
    { 
     this.name = name; 
     accounts = new Account[30]; 
    } 
    public void addAccount(Account acct) 
    { 
     accounts[count] = acct; 
     count++; 
    } 
    public void addInterest() 
    { 
     //for (Account acct : accounts) 
      //acct.addInterest(); 
     for(int i = 0; i < count; i++) 
      accounts[i].addInterest(); 
    } 
} 

我收到一個錯誤，如果我嘗試使用與 的addInterest（）方法（ACCT賬戶：賬戶）環你看到註釋掉。有人可以向我提供有關這是爲什麼的見解嗎？我認爲這些循環是相同的。提前致謝。

Answer 1

iterable數組上的for循環遍歷所有30個元素，而不僅僅是您真正添加的元素。

您可以使用ArrayList<Account>並根據需要添加元素。這可以讓您省略計數字段：

public class Bank 
{ 
    ArrayList<Account> accounts = new ArrayList<Account>(); 
    String name; 

    public Bank(String name) 
    { 
     this.name = name; 
    } 
    public void addAccount(Account acct) 
    { 
     accounts.add(acct); 
    } 
    public void addInterest() 
    { 
     for (Account acct : accounts) 
      acct.addInterest(); 
    } 
} 

Answer 2

您必須初始化帳戶陣列

，所以你可能要將此更改爲：

public void addInterest() 
    { 
     //for (Account acct : accounts) 
      //acct.addInterest(); 
     for(int i = 0; i < count; i++) 
      accounts[i].addInterest(); 
    } 

到這樣的事情：

 public void addInterest() 
     { 
      for (Account acct : accounts) { 
      acct= new Account("John",1234596069,200.00); 
      acct.addInterest(); 
      } 
//   for(int i = 0; i < count; i++) 
//    accounts[i].addInterest(); 
     } 

從本質上講，你必須初始化數組變量在調用方法之前。