Question

我需要在将子类发送到超类之前检查子类中接收的变量的值。

这就是我的超类

//superclass
public class Account 
{
    private double balance;

    public Account( double amount )
    {
            balance = amount;
    }

    public Account()
    {
            this(0.0);
    }

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

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

    public double getBalance()
    {
            return balance;
    }
}

这就是我的子类

public class SafeAccount extends Account
{

   public SafeAccount(double amount)
   {
      // something to check if amount is positive before sending it to 
         super 

      // if it's not positive, use no argument constructor to set balance == 
         0.0
   }
}

我想我应该使用＆＃34;这个（金额）＆＃34;以某种方式检查它，但我不确定这将如何工作。

Answer 1

super()必须是构造函数体中的第一个语句，因此您无法在它之前执行检查。

简单的解决方法：

 public class SafeAccount extends Account
{

   public SafeAccount(double amount)
   {
     super(Math.max(0.0, amount));
   }
}

如果你真的必须使用no arg构造函数，那么更复杂的解决方法是：

public class Account {
    Account() {

    }

    Account(double x) {

    }
}

public class SafeAccount extends Account {
    private SafeAccount() {

    }

    private SafeAccount(double amount) {
        super(amount);
    }

    public static SafeAccount boo(double x) {
        if (x < 0.0) {
            return new SafeAccount();
        }
        return new SafeAccount(x);
    }
}

在子类中使用private构造函数来阻止构造函数的实例化并提供执行所需检查的工厂方法。

Answer 2

您可以使用以下声明

@ECHO OFF
color 0b
title Display Selector by Nicholas Deckman
setlocal EnableExtensions EnableDelayedExpansion
CLS
echo       -----------------------------------
echo            Display Selector              
echo                     by Nicholas Deckman  
echo       -----------------------------------
echo.
echo.
:Begin
ECHO 1.PC Display Only
ECHO 2.External Display Only
ECHO 3.Extend Display
ECHO 4.Duplicate
ECHO.

CHOICE /C 1234 /M "Enter the number of your choice:"

:: Note - list ERRORLEVELS in decreasing order
IF ERRORLEVEL 4 GOTO Duplicate
IF ERRORLEVEL 3 GOTO Extend
IF ERRORLEVEL 2 GOTO External
IF ERRORLEVEL 1 GOTO Internal

:Internal
echo.
ECHO Internal Display Selected
displayswitch.exe /internal
GOTO Confirm

:External
echo.
ECHO External Display Selected
displayswitch.exe /external
GOTO Confirm

:Extend
echo.
ECHO Extend Display Selected
displayswitch.exe /extend
GOTO Confirm

:Duplicate
echo.
ECHO Duplicate Display Selected
displayswitch.exe /clone
GOTO Confirm

:Confirm
echo.
CHOICE /T 15 /D N /M "Is this the setting you would like to keep? If no option is selected in 15 seconds, the display will revert to [PC ONLY] Display: "

IF ERRORLEVEL Y GOTO YES
IF ERRORLEVEL N GOTO NO


:NO
echo.
ECHO Reverting to [PC ONLY] Display
ECHO Reverted Success!
echo.
GOTO InternalBegin

:InternalBegin
echo.
ECHO Internal Display Selected
displayswitch.exe /internal
GOTO Begin

:YES
echo.
color 4
ECHO CMD FAIL
ECHO Thank you for using the Display Selector Tool by Nicholas Deckman
pause
GOTO End

:End

但总的来说，需要重新检查这种继承层次结构的正确性。

在将子类发送到私有超类变量之前检查子类中的值

2 个答案: