責任鏈：余數算法？

Question

在以下方法中，我嘗試執行以下操作：

如果您至少有20英鎊：

• 算出20英鎊的面額

• 算出剩下的（剩余）–將其傳遞給下一個處理程序

• 如果您的存款少於£20，請致電下一位服務員

注意：該程序適用於ATM分配器，它根據用戶需要的量（數量）分配鈔票（20、10、5）。

到目前為止，以下是我的解決方案，我需要幫助來糾正算法

@Override
public void issueNotes(int amount) {
    //work out amount of twenties needed
    if(amount >= 20) {
        int dispenseTwenty;
        int remainder;
        dispenseTwenty = amount%20;
        remainder = amount = //call next handler?
    }
    else {
        //call next handler (as amount is under 20)
    }
}

Answer 1

沒關系的語法，請參見下文：

public static final denominators = [20,10,5]

// recursive function

// you can start calling this recursive function with denom_index=0, thus using denominator 20

public void issueNotes(int amount, int denom_index)

{

   int currentDenominator = denominators[denom_index];

   if(amount ==0) return; // no more dispensing

   if(denom_index >2) // remainder drop to below 5

    {

       throwException (" remaining amount not dispensable ");

    }


   if (amount < currentDenominator) // amount less than current denominator

    {

        issueNotes(amount, denom_index+1);

    }

   else

   {

        dispenseNotes(amount/currentDenominator, currentDenominator);

        // call the handler with remainder of the amount and next denominator

        issueNotes(amount%currentDenominator, denom_index+1);

   }

}

Answer 2

責任鏈模式取決於能否提供行為來處理請求消息-並可能對其進行處理。 如果處理程序無法處理請求，則調用下一個封裝的處理程序

兩個核心組成部分將是界面和具體

interface IMoneyHandler {
    void issueNotes(int money);
    void setNext(IMoneyHandler handler);
}

具體實施的示例可能是-

class TwentyMoneyHandler implements IMoneyHandler {
    private IMoneyHandler nextHandler;

    @Override
    public void issueNotes(int money) {
        int handlingAmount = 20;
        // Test if we can handle the amount appropriately, otherwise delegate it
        if(money >= handlingAmount) {
            int dispenseNotes = money / handlingAmount;
            System.out.println(dispenseNotes + " £20s dispenses");
            int remainder = money % handlingAmount;
            // Propagate the information to the next handler in the chain
            if(remainder > 0) {
                callNext(remainder);
            }
        } else {
            // call the next handler if we can not handle it
            callNext(money);
        }
    }

    // Attempts to call the next if there is money left
    private void callNext(int remainingMoney) {
        // Note, there are different ways of null handling
        // IE throwing an exception, or explicitly having a last element
        // in the chain which handles this scenario
        if(nextHandler != null) {
            nextHandler.issueNotes(remainingMoney);
        }
    }

    @Override
    public void setNext(IMoneyHandler handler) {
        this.nextHandler = handler;
    }
}

請注意，在現實世界中，您可能為此提供了一個抽象實現，以避免代碼重復。