如何编写一种方法来准确计算储蓄账户的余额，而不是银行储蓄账户和活期账户的余额？

Question

我正在创建一个名为 Bank 的 java 项目。 SavingsAccount 和 CurrentAccount 类是 Account 类的子类。在存储有关帐户信息的 Bank 类中，我必须创建一个方法来打印所有 SAVINGS 帐户的余额总和。我应该如何编写方法来准确总结储蓄账户的余额，而不是储蓄账户和活期账户？

import java.util.ArrayList;
public class Bank
{
    private ArrayList<Account> accounts;

    public Bank()
    {
        super();
        accounts = new ArrayList<Account>();

    }

    public void addAccount(Account theAccount)
    {
        accounts.add(theAccount);
    }

    public void getDescription()
    {
        for(Account account: accounts)
        {
            System.out.println("Name: " + account.getOwnerName() + "\nCode: " + account.getCode() + "\nBalance: " + account.getBalance());
        }
    }

    public double accountsSum()
    {
        double total = 0;
        for(Account acc: accounts)
        {
            total += acc.getBalance();
        }
        return total;
    }

    public void printSavingsBalance()
    {
            //?????    
    }
}



public class Account
{
    protected String code;
    protected String ownerName;
    protected double balance;

    public Account(String code,String ownerName, double balance)
    {
        this.code = code;
        this.ownerName = ownerName;
        this.balance = balance;
    }

    public String getCode(){return code;}

    public String getOwnerName(){return ownerName;}

    public double getBalance(){return balance;}

    public void setBalance(double newBalance)
    {
        balance = newBalance;
    }

    public void addMoney(double plusMoney)
    {
        balance += plusMoney;
    }

    public void withdrawMoney(double minusMoney)
    {
        balance -= minusMoney;
    }
}



public class SavingsAccount extends Account
{
    private int term;
    private double interestRate;

    public SavingsAccount(int term, double interestRate, String code, String ownerName, double balance)
    {
        super(code,ownerName,balance);
        this.term = term;
        this.interestRate = interestRate;
    }

    public int getTerm(){return term;}

    public double getInterestRate(){return interestRate;}

    public void setTerm(int newTerm)
    {
        term = newTerm;
    }

    public void setInterestRate(double newInterestRate)
    {
        interestRate = newInterestRate;
    }

    public double interestSize()
    {
        return balance*interestRate/365*term;
    }
}

Answer 1

可以使用instanceof判断对象的类型，只有类型为Savings时才求和。

int totalBalance = 0;
for(Account account: accounts){
   if (account instanceof Saving) {
      totalBalance = totalBalance + account.getBalance();
   }
}

Answer 2

private List<SavingsAccount> savingsAccounts;
private List<CurrentAccount> currentAccounts;

public addAccount(SavingsAccount account){

}

public addAccount(CurrentAccount account){

}

这样做会更好。然后只需遍历储蓄账户并添加所有账户的余额。引入 accountType 和 instanceof 检查将违反多态性恕我直言。

---

Visitor pattern 更简洁的方法：

public class Bank{

    private List<Account> accounts = new ArrayList<Account>();

    public void add(Account account) {
        accounts.add(account);
    }

    public double getBalance(){
        AdditionAccountVisitor visitor = new AdditionAccountVisitor();
        for(Account account : accounts){
            account.accept(visitor);
        }

        return visitor.getSum();
    }
}

abstract class Account{
    private double balance;

    public Account(double balance) {
        this.balance = balance;
    }

    public double getBalance(){
        return balance;
    }

    public abstract void accept(AccountVisitor visitor);
}

class SavingsAccount extends Account{

    public SavingsAccount(double balance) {
        super(balance);
    }

    @Override
    public void accept(AccountVisitor visitor) {
        visitor.visit(this);
    }

}

class CurrentAccount extends Account{

    public CurrentAccount(double balance) {
        super(balance);
    }

    @Override
    public void accept(AccountVisitor visitor) {
        visitor.visit(this);
    }
}

interface AccountVisitor{
    public void visit(SavingsAccount savingsAccount);
    public void visit(CurrentAccount savingsAccount);
}

class AdditionAccountVisitor implements AccountVisitor{
    private double sum = 0.0;

    @Override
    public void visit(SavingsAccount savingsAccount) {
        sum += savingsAccount.getBalance();
    }

    @Override
    public void visit(CurrentAccount savingsAccount) {
        //do nothing
    }

    public double getSum(){
        return sum;
    }
}

Answer 3

将accountType 字段添加到Account 类，可能是枚举类型（也可能是int 等）。然后在循环中检查帐户是否属于所需类型，然后再添加余额。

public void printSavingsBalance()
{
    double total = 0;
    for(Account acc: accounts)
    {
        if (acc.getType() == SAVINGS)
            total += acc.getBalance();
    }
    return total; 
}

或使用@Narendra Pathai 建议的 2 个列表 - 取决于您还想对帐户和列表做什么

Answer 4

如果您对使用 instanceof 的想法感到心烦意乱，请向您的超类添加一个虚拟方法，并在每个子类中定义它：

Savings:

String accountType() {
    return "Savings";
}

Checking:

String accountType() {
    return "Checking";
}