Question

帐户类定义为为银行帐户建模。帐户具有属性帐号，余额，年利率和创建日期，以及存入和取出资金的方法。

现在创建两个子类来检查和保存帐户。支票账户有透支限额（比如1000美元，收取25美元的费用），但储蓄账户不能透支。

编写一个创建Account，SavingsAccount和CheckingAccount对象的测试程序，并调用它们的toString（）方法。

以上是说明，以下是我的代码。我无法弄清楚如何将子类调用到主Account类中。我也想知道如何应用toString（）方法，因为我也无法得到它。我还在我的代码中保留了大部分注释，我在尝试不同的想法。

/* 

//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

我不确定你通过调用子类是什么意思，但是toString方法的签名是

public String toString(){
}

由于默认情况下Java中的所有内容都是虚拟的，因此只需在子类中使用该方法来覆盖它。根据我的猜测，似乎问题是你想要调用toString方法中的各种方法并返回所需的所有信息的完整字符串。

另一方面，要调用超类方法，即使子类在Java中重写它，语法也是

super.function()

Answer 2

首先，您需要为储蓄帐户和支票帐户创建默认构造函数。然后你需要创建一个重载的构造函数（假设你将唯一的额外值传递给子类）

 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

}

对于toString（），您需要每个子类都有自己的。

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

这样您就可以拨打savingsAccount.toString();来打印信息。

Answer 3

您需要覆盖每个类的默认toString方法例如，在Account类

中

    @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，在主类中创建Account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： Id：1122 余额：20000.0 年利率：0.0 每月利息：0.0 创建于：2月18日星期四18:16:47太平洋标准时间2016

类似地，您还需要为子类重写toString方法。但是你需要使用super关键字来连接超类的toString：

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

创建两个子类来检查和保存帐户。支票账户有透支限额，但储蓄账户不能透支

3 个答案: