创建两个子类，用于检查和储蓄账户。活期存款有一个透支额度，但储蓄账户不能透支

Question

Account类被定义为一个银行帐户进行建模。一个帐户的属性账号，余额，年利率，和创建日期和方法来存取资金。

现在，创建两个子类，用于检查和储蓄账户。活期存款有一个透支额度（说与收取$ 25费$ 1,000），但储蓄账户不能透支。

编写创建帐户，SavingsAccount，和的CheckingAccount的对象，并调用其toString（）方法的测试程序。

以上是下面的说明和是我的代码。我无法弄清楚如何子类调用到主账户类。我也想知道toString（）方法如何应用，因为我无法获得，要么。我还不停的大部分我在我的代码中的注释，我是想不同的想法。

---

/* 

//Calls both subclasses to the main. As well as a few other variables.  
SavingsAccount savings = new SavingsAccount();
CheckingAccount checking = new CheckingAccount();
Account account;


    double balance = 0.0;
    double withdrawal = 0.0;
    double deposit = 0.0;

    System.out.println(checking);
    CheckingAccount.getwithdrawal(10.50);
    System.out.println(savings);
    SavingsAccount.deposit(5.0);
    System.out.println(account);
     }    
}

 */

 package account;



  public class Assignment5  {

   SavingsAccount savings = new SavingsAccount();
   CheckingAccount checking = new CheckingAccount();
   Account account;

   public static void main (String[] args) {
   Account account = new Account(1122, 20000);

  /* System.out.print("After Creation,  " );
   Print (account.getBalance());
  Account.setAnnualInterestRate(4.5);
   System.out.print("After Withdrawal of $2,500,  " );
   account.withdraw(2500);
   Print (account.getBalance());
    System.out.print("After Deposit of $3,000,  " );
    account.deposit(3000);
   Print (account.getBalance());
    System.out.println("Balance is " + account.getBalance());
    System.out.println("Monthly interest is " +
  account.getMonthlyInterest());
    System.out.println("This account was created at " +
  account.getDateCreated()); */

    } 
  // Extra Print Method
     public static void Print (double x){
     System.out.printf("The current balance is "+" $ "+"%4.2f"+"%n",x);
    }
  }



  class Account {
  private int id;
   double balance;
   private static double annualInterestRate;
   private java.util.Date dateCreated;

  public Account() {
    dateCreated = new java.util.Date();
  }

  public Account(int newId, double newBalance) {
     id = newId;
     balance = newBalance;
     dateCreated = new java.util.Date();
   }

  public int getId() {
    return this.id;
      }

   public double getBalance() {
    return balance;
    }

     public static double getAnnualInterestRate() {
      return annualInterestRate;
      }

    public void setId(int newId) {
     id = newId;
     }

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

  public static void setAnnualInterestRate(double newAnnualInterestRate) {
    annualInterestRate = newAnnualInterestRate;
  }

 public double getMonthlyInterest() {
   return balance * (annualInterestRate / 1200);
 }

  public java.util.Date getDateCreated() {
   return dateCreated;
  }

   public void withdraw(double amount) {
    balance -= amount;
 }

    public void deposit(double amount) {
    balance += amount;
   }
  }

---

 package account;

 public class CheckingAccount extends Account {


double overDraft = -1000;

    public void checking(double i) {

        //initializes double variable balance as 0.0
        double balance = 0.0;
        if (balance - i < overDraft){
                System.out.println("Failure: Can't overdraft more than            $1,000. A $25 +"
                        + "overdraft fee will be issued to your account. ");
             balance = balance - 25; }
        else
            balance = balance - i;
      }   
  }

---

  package account;

  public class SavingsAccount extends Account{
    double overdraftLimit = 0;

    public void withdraw (double w) {
        if (balance - w < overdraftLimit)
                System.out.println("Insufficient Funds");
        else
            balance = balance - w;
    }
}

Answer 1

我不知道你通过调用子类的意思，但对于toString方法签名

public String toString(){
}

既然一切都虚拟在Java中默认，然后只需在子类的方法来覆盖它。从我可以猜到，这似乎是这个问题要你调用toString方法的各种方法和返回所需的所有信息的完整字符串。

在另一方面，调用父类方法，即使子类覆盖它在Java中，语法是

super.function()

Answer 2

首先，你需要创建一个默认的构造函数储蓄存款和支票账户。然后，你需要创建一个重载的构造函数（假设你将被传递的唯一的额外的值到子类）

 public savingsAccount() {
super();
}
//overloaded constructor
public savingsAccount(int newId, double newBalance, int anotherVariable ) {
 super(newID, newBalance);
 this.anotherVariable = anotherVariable; //this is unique to this specific class

}

至于的toString（），你需要在每个子类有它自己的。

String toString(){
 String x = "Savings: " + totalSavings + ". And the fee's assessed are: " + fees";
  return x;
}

这将允许你打电话savingsAccount.toString();，它将打印信息。

Answer 3

你需要重写每一个类例如默认的toString方法，在Account类

    @Override
    public String toString()
    {
        String str = "Id: "+ getId() +
                     "\nBalance:  " + getBalance()+
                     "\nAnnual Interest Rate: " + getAnnualInterestRate() +
                     "\n Monthly Interest: " + getMonthlyInterest() +
                     "\n Created on: " + getDateCreated();

        return str;
    }

然后，创建主类帐户对象

public static void main(String[] args) {
    // TODO Auto-generated method stub
    Account account = new Account(1122, 20000);
    System.out.println(account); // invoke toString method in Account class
}

结果将是：编号：1122余额：20000.0年利率：0.0月息0.0创建于：周四02月18日十五时16分47秒的PST 2016

同样，你需要重写的子类的toString方法也。但是，你需要使用super关键字来超的toString连接：

public String toString()
{
    String str=super.toString();// call superclass's toString()
    str+="...";
    return str;
}