JAVA - 两个对象之间的关系

Question

我对 OOP 和 Java 还是很陌生，有一个问题可能很简单，但我在网上找不到答案。

我正在用 Java 编写标准银行账户程序 - 一个有客户的程序，每个客户都有银行账户（一个客户可能有多个银行账户！），我可以存款或取款。每个银行账户都有一个唯一的号码（即使某人有多个银行账户，每个银行账户都有唯一的号码）

我的代码编译成功，存款和取款操作正常。

问题如下 - 我不能将多个银行帐户归于一个客户，在我的程序中，客户只能拥有一个银行，但不能超过一个银行帐户。

我有 3 个类 - Account、Client、BankMain。你可以在下面看到它们

public class Account {
    private int balance;
    private String NumAccount; // each bank account has a unique number

    public Account(int money, String num) {
        balance = money;
        NumAccount = num;
    }

    public String printAccountNumber() {
        return NumAccount;
    }
    // below are the methods for withdraw,deposit- they are working properly
}

类客户端

public class Client {
    private String name;// name of the client
    private Account account;

    // the account associated to the client. Probably I should change sth
    // here
    // but I don't know what
    public Client(String nom, Compte c) {
        name = nom;
        account = c;
    }

    public void printName() {
        System.out.println(
                "Name: " + name 
                + "\nAccount number: " + account.printAccountNumber() 
                + "\nSolde: " + account.printBalance() + "\n"
        );
    }
}

和BankMain

public class BankMain {

    public static void main(String[] args) {
        Account account1 = new Account(1000, "11223A");
        Account account2 = new Account(10000, "11111A");
        Client client1 = new Client("George", account1);
        Client client2 = new Client("Oliver", account2);
        // now this is working correctly
        client1.printName();
        client2.ptintName();
        /*
         * The problem is that I don't know what to do if I want account1
         * and account2 to belong both to client1. I tried Client client1 =
         * new Client("George",account1); Client client1 = new
         * Client("Oliver", account2); but got compilation error
         */
    }
}

你知道我该如何解决这个问题吗？我应该怎么做才能让多个银行账户关联到同一个客户？

提前致谢 乔治

Answer 1

查看此代码：

//Account

public class Account
{
    private int balance;
    private String accNo;

    public Account(int money,String num) {
    balance = money;
    accNo = num;
}

public int getBalance() {
        return balance;
    }

public void setBalance(int balance) {
    this.balance = balance;
}

public String getAccNo() {
    return accNo;
}

public void setAccNo(String accNo) {
    this.accNo = accNo;
}

}

//Client 

import java.util.ArrayList;
import java.util.Collection;

public class Client 
{
    private String clientName;
    private HashSet<Account> accounts;
public Client(String name)
{
    this.clientName = name;
    this.accounts = new HashSet<Account>();
}

public void addAccount(Account account) {

    accounts.add(account);
}

public String getClientName() {
    return clientName;
}

public void setClientName(String clientName) {
    this.clientName = clientName;
}

public Collection<Account> getAccounts() {
    return accounts;
}

public void setAccounts(HashSet<Account> accounts) {
    this.accounts = accounts;
}

public void printAccountDetails() {

    System.out.println("Account details :");
    int counter= 0;
    for(Account acc : accounts) {
        counter ++;
        System.out.println("Account details for Account '"+counter+"' :\n");
        System.out.println("Account Number : "+ acc.getAccNo() +" Balance :" + acc.getBalance() );
    }
}

}

// Bank class


 public class BankMain {

    public static void main(String[] args) 
    {

        Account account1 = new Account(1000,"11223A");
        Account account2 = new Account(10000,"11111A");
        Client client = new Client("George");

        client.addAccount(account1);
        client.addAccount(account2);

        client.printAccountDetails();
    }

}

您可以在此处添加任意数量的帐户。

Answer 2

您可以为一个客户拥有多个帐户，更改Client 类中的数据类型。例如：

private Map<String, Account> accounts;

其中map的key是账号，value是账号本身。这样您就可以通过其唯一编号访问每个帐户。

（如果您不知道地图是什么，请查看this）

这也意味着您需要修改 Client 构造函数以接受多个帐户，或者添加新方法以将新帐户添加到 Client。

Answer 3

正如@m0skit0 建议的那样，使用地图或列表来保存 Client 类下的 Account 对象。

public class Client 
{
    private String name;//name of the client
    private List<Account> accounts = new ArrayList<Account>();

    public Client(String nom, Account c)
    {
        name = nom;
        accounts.add (c);
    }

    public boolean addAccount (Account c) 
    {
        return accounts.add (c);
    }
    public removeAccount (Account c)
    {
        final int accountIndex = accounts.indexOf (c);
        if (accountIndex > 0)
        {
            accounts.remove (accountIndex);
            return true;
        }
        return false;
    }

    public void printName()
    {
        System.out.println("Name: " + name);
        System.out.println ("Total Accounts: " + accounts.size());
        for (int i=0; i<accounts.size(); i++)
        {
             final Account a = accounts.get(i);
             System.out.println ("\tAccount Number: " + a.printAccountNumber());
             System.out.println ("\tAccount Balance: " + a.printBalance());
        }        
    }
}

并在您的 BankMain.java 中使用它

Account account1 = new Account(1000,"11223A");
Account account2 = new Account(10000,"11111A");
Client client1 = new Client("George", account1);
client1.addAccount (account2);

client1.printName();

Answer 4

而不是像这样尝试重新定义 client1 和 2：

Client client1 = new Client("George",account1);
Client client1 = new Client("Oliver", account2);

将这些对象重新定义为：

 client1 = new Client("George",account1);
 ...
 client1 = new Client("Oliver", account2);

但是这样做，您可以在同一个帐户上操作，即如果您现在执行 client1.withdraw，您将从 Oliver 的帐户中撤出，而不是 George。

您可以不这样做，而是在地图中维护名称和帐户对象，并给定名称，您可以随时获取该人的帐户。喜欢：

Map<String, Account> nameAccountMap = ..

然后你添加相应的帐户，如：

nameAccountMap.put("Oliver", account2);
nameAccountMap.put("George",account1);

现在，如果您希望对 Oliver 拥有的帐户进行操作，您可以通过以下方式进行操作：

nameAccountMap.get("Oliver").withdraw...

以及对其他账户持有人的类似操作。

如果您希望将多个帐户与一个用户关联，您可以使用用户持有的帐户名称和列表维护地图，例如：

    Map<String, List<Account>> nameAccountMap = ..

Answer 5

不要在您的 Client 类中使用单个 Account，而是使用 Set<Account> 以便建立一对多关系。确保 Account 类已实现 equals 和 hashcode。

public class Client 
{
    private String name;//name of the client
    private Set<Account> accounts;
 //the account associated to the client. Probably I should change sth here
 // but I don't know what
    public Client(String nom, Set<Account> c)
    {
        name = nom;
        account = c;
    }
    public String getName()
    {
        return this.name;
    }

   public Set<Account> getAccounts()
   {
       return this.accounts;
   }
   public String toString()
   {
       ...
       // Return description of the Object state
   }
}





public class Account
{
    private int balance;
    private String NumAccount; //each bank account has a unique number
    public Account(int money,String num)
    {
        balance = money;
        NumAccount = num;
    }
    public String getAccountNumber()
   {
        return NumAccount;
   }
   public boolean equals(..)
   {
       ...
   }
   public int hashcode()
   {
      ...
   }
   public String toString()
   {
       ...
       // Return description of the Object state
   }
    // below are the methods for withdraw,deposit- they are working properly
}