实施更好的战略模式

Question

我有一个支票账户和一个储蓄账户。我正在探索如何使用策略模式实现取款方法。

目前，支票账户和储蓄账户都继承自Account。对于储蓄账户，提款不应导致余额低于 100 美元。对于支票账户，提款必须包含支票号码。

我对使用这种方法没有信心，因为正如您将在下面看到的，“otherArguments”参数在一种情况下完全没有用。我这样做的唯一原因是“展示”策略模式的使用。

（对于那些关心的人，这是学校项目的一部分，下面的所有代码都是我编写的，我很好奇是否有更好的方法来完成它）。

这是我到目前为止所做的：

public abstract class Account
{
    public double Balance{get; set;}

    public WithdrawStrategy Withdrawer
    {
        get; set;
    }


    public abstract void withdraw(double currentBalance, double amount, object otherArguments);
}

public class Chequing: Account
{
    public Chequing()
    {
        Withdrawer= new ChequingAccountWithdrawer();
    }


    public override void withdraw(double currentBalance, double amount, object otherArguments)
    {
        if (null != Withdrawer)
        {
            double balance = Withdrawer.withdraw(currentBalance, amount, otherArguments);
            Balance = balance;
        }
    }    
}

public class Saving: Account
{
    public Saving()
    {
        Withdrawer= new SavingAccountWithdrawer();
    }


    public override void withdraw(double currentBalance, double amount, object otherArguments)
    {
        if (null != Withdrawer)
        {
            double balance = Withdrawer.withdraw(currentBalance, amount, otherArguments);
            Balance = balance;
        }
    }    
}

public interface WithdrawStrategy
{
    double withdraw(double currentBalance, double amount, object otherArguments);
}

public ChequingAccountWithdrawer: WithdrawStrategy
{
    public double withdraw(double currentBalance, double amount, object otherArguments)
    {
        string cheqNum = otherArguments.ToString();
        if (!string.IsNullOrEmpty(cheqNum))
        {
            currentBalance -= amount;
        }
        return currentBalance;
    }
}

public SavingAccountWithdrawer: WithdrawStrategy
{
    public double withdraw(double currentBalance, double amount, object otherArguments)
    {
        if (currentBalance - amount > 100) //hard code for example's sake
        {
            currentBalance -= amount;
        }
        return currentBalance;
    }
}

Answer 1

在使用策略模式时，您可能必须提供实际上无用的信息。这是负面后果之一。另一种解决方案是通过构造函数将必要的信息传递到策略对象中。这可确保策略对象具有所需的最少信息量。

如果 100 个最小值是唯一的算法差异，那么更好的解决方案可能是模板方法。

这是示例代码。

public abstract class Account
{
    public double Balance{get; set;}
    public abstract void withdraw();
}

public class Chequing: Account
{
    public override void withdraw()
    {
        //It's not clear where the values for your constructor come from, but
        //you get the idea.
        WithdrawStrategy withdrawer= new ChequingAccountWithdrawer();
        /////////////////////////////////////////////////////////////
        double balance = Withdrawer.withdraw();
        Balance = balance;
    }    
}

public class Saving: Account
{
    public override void withdraw()
    {
        //Same idea here.
        WithdrawStrategy withdrawer= new SavingAccountWithdrawer();
        /////////////////////////////////////////////////////////////
        double balance = Withdrawer.withdraw();
        Balance = balance;
    }    
}

public interface WithdrawStrategy
{
    double withdraw();
}

public ChequingAccountWithdrawer: WithdrawStrategy
{
    private readonly int balance;
    private readonly double amount;
    private readonly string number;

    public ChequingAccountWithdrawer(double aBalance, double aAmount, string aNumber) {
        balance = aBalance
        amount = aAmount
        number = aNumber
    }

    public double withdraw()
    {
        if (number)
        {
            currentBalance -= amount;
        }

        return currentBalance;
    }
}

public SavingAccountWithdrawer: WithdrawStrategy
{
    private readonly int balance;
    private readonly double amount;

    public SavingAccountWithdrawer(double aBalance, double aAmount) {
        balance = aBalance
        amount = aAmount
    }

    public double withdraw()
    {
        if (currentBalance - amount > 100) //hard code for example's sake
        {
            currentBalance -= amount;
        }

        return currentBalance;
    }
}

有一些代码重复。因为这是家庭作业，所以你能做的并不多。如果这是我的决定，我会立即抽象出这些字段。