java - 从父类的对象数组列表中调用子类的方法

Question

我已经搜索过这个问题的解决方案，但我仍然不明白该怎么做。这个程序应该模仿一台自动取款机，它用支票从余额中减去，用存款加钱。

我有这个父类:

public class Transaction
{

private int transNumber;
private int transId;
private double transAmt;

public Transaction(int number, int id, double amount)
{
    transNumber = number;
    transId = id;
    transAmt = amount;
}

public int getTransNumber()
{
    return transNumber;
}

public int getTransId()
{
    return transId;
}

public double getTransAmount()
{
    return transAmt;
}
}

我有一个数组列表 (transList)，用于存储每次取款/存款的交易对象。

子类是:

public class Check extends Transaction
{
private int checkNumber; // check number for each check transaction

public Check(int tId, double tAmt, int tCount, int checkNumber) {
    super(tCount, tId, tAmt);
    this.checkNumber = checkNumber;
}

public int getCheckNumber() {
    return checkNumber;
}

public void setCheckNumber(int checkNumber) {
    this.checkNumber = checkNumber;
}
}

我需要做的是在 JOptionPane 中打印出用户要求的支票号码。

主要有:

checkNumStr = JOptionPane.showInputDialog("Enter check number:");
                checkNum = Integer.parseInt(checkNumStr);
                checkAmtStr = JOptionPane.showInputDialog("Eneter check amount:");
                checkAmt = Double.parseDouble(checkAmtStr);

                Check c = new Check(1, checkAmt, acctCheck.gettransCount(), checkNum);

                acctCheck.addTrans(c);

我不确定我是否说得足够清楚。我以前没有在这里问过问题。我需要知道的是如何从父类 Transaction 的对象数组列表中调用 Check.getCheckNumber()。

编辑:transList 位于另一个类:支票账户:

public class CheckingAccount extends Account
{
  private double totalServiceCharge;
  private static ArrayList<Transaction> transList;
  // keeps a list of Transaction objects for the account
  private int transCount = 0;   
  // the count of Transaction objects and used as the ID for each transaction
  NumberFormat fmt = NumberFormat.getCurrencyInstance();



  public CheckingAccount()
  {
      transList = new ArrayList<Transaction>();
      totalServiceCharge = 0;
  }

  public double getServiceCharge()
  {
        return totalServiceCharge;
  }

    public void setServiceCharge(double currentServiceCharge)
  {
        totalServiceCharge += currentServiceCharge;
  }

    // adds a transaction object to the transList
    public void addTrans(Transaction newTrans)
    {
        transList.add (newTrans);
        transCount++;
    }

    //returns the current value of transCount;
    public int gettransCount()
    {
        return transCount;
    }
}

Answer 1

在构建类时，您应该考虑has-a is-a 关系。

你的例子，

您有一个 Transaction 类。您有一个 Check 类，它扩展了 Transaction。当您扩展时，您是在说Check is-a Transaction，这是不正确的。但是 Transaction has-a(或有一个)Check 吗？是的!因此，在这种情况下，您可以将 Check 与 Transaction 的扩展分开，并执行如下操作:

public class Transaction {
    Check check;  // This is an example of a has-a relationship
} 

public class Check {  // notice how Check doesn't extend Transaction
                      // anymore.  As it shouldn't, because they don't
}                     // share any common properties

如果你想要一个 Check 的 ArrayList，我会把它放在 Account 类中，因为 Account does has-a(有一个)checkHistory

public class Account {
    ArrayList<Check> checkHistory = new ArrayList<Check>();

    public ArrayList<Check> getCheckHistory() {
        return checkHistorty;
    }
}

因此您可以从 Account 类中调用 checkHistory，这很有意义

Account myAccount = new Account();

ArrayList<Check> list = myAccount.getCheckHistory();

for (Check check : list) {
    System.out.print(check.someCheckProperty);
}