好吧，请给情况做序。我被分配了多项任务。到目前为止，我已经创建了一个Canteen Account（将在下面显示），这是一个主菜单类，现在我必须制作另一个从Canteen Account继承的类，称为StaffAccount。 StaffAccount对象应包含以下附加属性：
discountRate-应用于所有购买的折扣率（百分比）
StaffAccount对象应包含以下其他方法：
（i）StaffAccount（字符串newId，字符串newName，双倍DiscountRate）
通过三个参数初始化StaffAccount对象的属性的构造方法。
在员工帐户中，我遇到了一个称为PayForMeal的方法（这是一个被覆盖的方法），该方法在任务摘要中的目的是：
一种记录餐费的方法。应该修改StaffAccount对象的余额，以反映用餐费用的折扣（如果费用不超过可用余额）。
如果费用超过余额，则会引发异常以警告客户他们必须补充余额–如果客户在其信用额度之内，则余额中将记录负值，并且帐户状态更改为表明客户正在使用信用。 如果客户使用的是信用额，则不应应用折扣。
所以我的问题是，如何使用给定的构造函数创建一个员工帐户，然后使用payForMeal覆盖的方法对餐费金额进行折扣，然后从余额中扣除折扣后的金额不存在，因为它不在StaffAccount的构造函数中，但在CanteenAccount的构造函数中。这些课程在下面，我只想知道这是否可行或者我很笨
/////// CANTEEN帐户\\\\\\\\
public class CanteenAcc
{
private String customerId;
private String name;
private double balance;
private static double minTopup = 2.00;
private String status;
private static double creditLimit = 5.00;
private static int transCount;
/**
* Constructor to create a Canteen account object using three parameters
* @param newId - String
* @param newName - String
* @param newBalance - Double
*/
public CanteenAcc(String newId, String newName, double newBalance)
{
this.customerId = newId;
this.name = newName;
this.balance = newBalance;
}
public CanteenAcc(String newId, String newName)
{
this.customerId = newId;
this.name = newName;
}
//BEFORE EVERY METHOD AND CLASS YOU SHOULD HAVE JAVADOC COMMENTS.
public void topUp(double depositAmount)
{
if(depositAmount > 0)
{
this.balance += depositAmount;
this.status = "Valid";
}else
{
this.status = "Invalid";
}
}
public void payForMeal(double amount) throws Exception
{
if(balance - amount < 0 && amount - balance <= creditLimit)
{
this.status = "Using Credit";
double newBalance = balance - amount;
balance = newBalance;
throw new Exception("\n\n-----------------------------\n"
+ "You must top-up your balance\n"
+ "Your new balance is: "+ balance + " GBP" +"\n"
+ "You are: " + status + "\n"
+ "-----------------------------\n");
}
else if(amount > creditLimit && balance < amount)
{
throw new Exception("\n\n------------------------------\n"
+ "Cost exceeds the credit limit."
+ "\n------------------------------\n");
}
else
{
double newBalance = balance - amount;
balance = newBalance;
transCount++;
}
}
public String displayAccountDetails()
{
StringBuilder ad = new StringBuilder();
ad.append("------------------------\n");
ad.append("****Account Details****\n");
ad.append("------------------------\n");
ad.append("\n");
ad.append("****Customer ID****: \n" + customerId + "\n");
ad.append("\n");
ad.append("****Name****: \n" + name + "\n");
ad.append("------------------------\n");
ad.append("\n");
return ad.toString();
}
public String getStatistics()
{
StringBuilder as = new StringBuilder();
as.append("------------------------\n");
as.append(" CANTEEN ACCOUNT \n");
as.append("------------------------\n");
as.append("\n");
as.append("****Transaction Count****\n");
as.append(transCount + "\n");
as.append("\n");
as.append("****Account Balance****\n");
as.append(balance + "\n");
as.append("\n");
as.append("***Account Status****\n");
as.append(status + "\n");
as.append("------------------------\n");
return as.toString();
}
public double getBalance()
{
return balance;
}
public double getCreditLimt()
{
return creditLimit;
}
public double getMinTopup()
{
return minTopup;
}
public String getStatus()
{
return status;
}
public static void updateCreditLimit(double newLimit)
{
creditLimit = newLimit;
}
public static void updateMinTopup(double newTopup)
{
minTopup = newTopup;
}
}
/////////主要方法///////////////////////
public class Test
{
public static void main(String[] args) {
String menuItems[] = {"1. Top up account ", "2. Pay for meal ", "3. Display Account Status",
"4. Display Account Balance ", "5. Display Account Details ",
"6. Update credit limit ", "7. Update Minimum top-up ", "8. Exit program"};
Menu myMenu = new Menu("Holiday Account", menuItems) ;
int choice;
Scanner keyb = new Scanner(System.in);
choice = myMenu.getChoice() ;
do{
choice = myMenu.getChoice();
//CanteenAcc Employee = new CanteenAcc("A01PL", "Patrick", 2);
CanteenAcc Employee2 = new StaffAccount("blah", "blah", 0.25);
switch (choice)
{
case 1 : System.out.println("How much would you like to top-up: ");
double deposit = keyb.nextDouble();
Employee2.topUp(deposit);
System.out.println("Your balance is: £" + Employee2.getBalance());
break ;
case 2: System.out.println("Input how much your meal costs: ");
try {
double amount = keyb.nextDouble();
Employee2.payForMeal(amount);
System.out.println("Your meal cost: " + amount);
} catch(Exception ex)
{
System.out.println(ex.toString());
}
System.out.println("Your balance is: £" + Employee2.getBalance());
break ;
case 3: System.out.println(Employee2.getStatus());
break;
case 4: System.out.println("£" + Employee2.getBalance());
break;
case 5: System.out.println(Employee.displayAccountDetails());
break;
case 6: System.out.println("What amount would you like the new limit to be: ");
double newLimit = keyb.nextDouble();
CanteenAcc.updateCreditLimit(newLimit);
System.out.println("The new credit limit is: " + newLimit);
case 7: System.out.println("What amount would you like the new limit to be: ");
double newMinTopup = keyb.nextDouble();
CanteenAcc.updateMinTopup(newMinTopup);
System.out.println("The new minimum topUp is: " + newMinTopup);
case 8: System.exit(0);
}
}//End DoWhile
while(choice != 8);
}
}
////工作人员帐户///////
public class StaffAccount extends CanteenAcc
{
private double discountRate;
public StaffAccount(String newId, String newName, double discountRate)
{
super (newId, newName);
this.discountRate = 0.25;
balance = 0;
}
public void setDiscountRate(double rate)
{
discountRate = rate;
}
public double getDiscountRate()
{
return discountRate;
}
public void payForMeal(double amount) throws Exception
{
amount = amount/discountRate;
super.payForMeal(amount);
}
}
答案 0 :(得分：0)
确定：
您有一个CanteenAcc：很好。您还拥有一个从CanteenAcc继承的StaffAccount。也很好。
您应使用@Override：When do you use Java's @Override annotation and why?
您的变量名都应以小写字母开头，例如CanteenAcc employee2 = new StaffAccount("blah", "blah", 0.25);。
updateCreditLimit（）和updateMinTopup（）应该不是是静态的（因为每个不同的对象可能具有不同的值）：Java: when to use static methods
...最后...
使用CanteenAcc employee = new CanteenAcc("A01PL", "Patrick", 2);，则employee.payForMeal（）将具有“ CanteenAcc”行为。
使用CanteenAcc employee2 = new StaffAccount("blah", "blah", 0.25);，则employee2.payForMeal（）将具有“ StaffAccount”行为。
您发布的代码有些错误。我希望您有一个IDE，并通过示例测试值逐步调试程序。
但是对于您的原始问题：
您在正确的轨道上。
我在上面提到了几个“次要”问题。
我不确定您为什么担心“构造函数”。面向对象语言（如Java）的工作方式-如果定义了正确的基类，并在子类中适当地“专门化”了行为，则-通过“继承”的魔力-一切“都可以正常工作”。
我稍微修改了您的代码，并编写了另一个“测试驱动程序”。这是代码，以及输出：
StaffAccount.java
package com.example;
public class StaffAccount extends CanteenAccount {
private double discountRate;
public StaffAccount(String newId, String newName, double discountRate) {
super(newId, newName);
this.discountRate = discountRate; // Set this to "discountRate", instead of hard-coding 0.25
// You'll note that "balance" is implicitly set to "0.0" in the base class
}
public void setDiscountRate(double rate) {
discountRate = rate;
}
public double getDiscountRate() {
return discountRate;
}
@Override
public void payForMeal(double amount) throws Exception {
amount = amount / discountRate;
super.payForMeal(amount);
}
}
TestAccount.java
package com.example;
/**
* Test driver
* In a "real" application, I would implement these as a suite of JUnit tests
*/
public class TestAccount {
private static void buyAMeal (CanteenAccount person, double cost) {
try {
person.payForMeal(cost);
} catch (Exception e) {
System.out.println ("ERROR: " + e.getMessage());
}
}
public static void main(String[] args) {
System.out.println (">>Creating employee (\"CanteenAccount\" and employee2 (\"StaffAccount\") objects...");
CanteenAccount employee = new CanteenAccount("A01PL", "Patrick", 2);
CanteenAccount employee2 = new StaffAccount("blah", "blah", 0.25);
System.out.println (">>Checking initial balances...");
System.out.println (" employee balance=" + employee.getBalance() + ", creditLimit=" + employee.getCreditLimit());
System.out.println (" employee2 balance=" + employee2.getBalance() + ", creditLimit=" + employee2.getCreditLimit());
System.out.println (">>Buying a $5.00 meal...");
System.out.println (" employee...");
buyAMeal (employee, 5.00);
System.out.println (" employee balance=" + employee.getBalance() + ", creditLimit=" + employee.getCreditLimit());
System.out.println (" employee2...");
buyAMeal (employee2, 5.00);
System.out.println (" employee2 balance=" + employee2.getBalance() + ", creditLimit=" + employee2.getCreditLimit());
System.out.println (">>Add $5.00 and buy another $5.00 meal...");
System.out.println (" employee...");
employee.topUp(5.0);
buyAMeal (employee, 5.00);
System.out.println (" employee balance=" + employee.getBalance() + ", creditLimit=" + employee.getCreditLimit());
System.out.println (" employee2...");
employee2.topUp(5.0);
buyAMeal (employee2, 5.00);
System.out.println (" employee2 balance=" + employee2.getBalance() + ", creditLimit=" + employee2.getCreditLimit());
}
}
示例输出：
>>Creating employee ("CanteenAccount" and employee2 ("StaffAccount") objects...
>>Checking initial balances...
employee balance=2.0, creditLimit=5.0
employee2 balance=0.0, creditLimit=5.0
>>Buying a $5.00 meal...
employee...
ERROR:
-----------------------------
You must top-up your balance
Your new balance is: -3.0 GBP
You are: Using Credit
-----------------------------
employee balance=-3.0, creditLimit=5.0
employee2...
ERROR:
------------------------------
Cost exceeds the credit limit.
------------------------------
employee2 balance=0.0, creditLimit=5.0
>>Add $5.00 and buy another $5.00 meal...
employee...
ERROR:
-----------------------------
You must top-up your balance
Your new balance is: -3.0 GBP
You are: Using Credit
-----------------------------
employee balance=-3.0, creditLimit=5.0
employee2...
ERROR:
------------------------------
Cost exceeds the credit limit.
------------------------------
employee2 balance=5.0, creditLimit=5.0