BlueJ错误：不兼容的类型：int无法转换为java.lang.String（票证机模拟）

我对java非常陌生，在尽我所能用bluej创建了一个票证机之后，我真的不知道该怎么做

 public class CarParkTicketMachine
{
    private double RunningBalance;
    private double CurrentBalance;
    private String CarReg;
    private static double MinTicketCharge = 0.7;

    //Constructor
    public CarParkTicketMachine()
    {
        RunningBalance = 0;
        CurrentBalance = 0;
    }

    //Try and request a ticket
    public void RequestTick()
    {
        if(Validate())
        {
            //Create a ticket for the customer
            CarParkTicket ticket = new CarParkTicket (CarReg, CurrentBalance);
            //keep a running total
            RunningBalance += CurrentBalance;
            //clear the customer's balance
            CurrentBalance = 0;
            //print ticket for the customer
            ticket.PrintTicket();
        }
    }

    //Perform check to ensure we can purchase a ticket
    private boolean Validate()
    {
        boolean valid = false;

        //Check that the user has entered their car registration
        if(!(CarReg == null || CarReg.isEmpty())) //must NOT be null
        {
            //Check that the user has entered enough money
            if(CurrentBalance >= MinTicketCharge)
            {
                return true;
            }
            else
            {
                System.out.println("You have not entered enough money");
            }
        }
        else
        {
            System.out.println("Please enter your car registration");
        }
        return false;
    }
}

public class CarParkTicket
{
    //Customer's Car Registration
    private String CarRegistration; 
   //Cost of the ticket
   private double charge;

   public CarParkTicket (String CarReg, double charge)
   {
       CarRegistration = CarReg;
       double Charge = charge;
    }

    public void PrintTicket()
    {
        System.out.println("*****************");
        System.out.println("Your Ticket");
        System.out.println("Registration:" + CarRegistration);
        System.out.println("Cost: £" + charge );
        System.out.println("*****************");
    }
}

public class Coin
{
    //property to hold the value of the coin
    private double Value;

    //Constructor
    public Coin(double value)
    {
        this.Value = value;
    }

    //accessor
    public double GetValue()
    {
        return Value;
    }
}

我的三个类编译没有任何问题，但是当我创建“CarParkTicketMachine”的新对象并尝试输入设置汽车注册或插入硬币的方法调用时，我得到一个“错误：找不到符号-变量”

我觉得问题在于这一部分，但由于我对java/bluej非常陌生，我真的不知道如何解决这个问题：

private Boolean Validate()
    {
        boolean valid = false;

        //Check that the user has entered their car registration
        if(CarReg == (" "))
        {
            //Check that the user has entered enough money
            if(CurrentBalance >= MinTicketCharge)
            {
                valid = true;
            }
            else
            {System.out.println("You have not entered enough money");
            }
        }
        else
        {
            System.out.println("Please enter your car registration");
        }
        return valid;
    }

---

以下是我对验证的建议： 请注意，您正在尝试检查用户是否已输入，然后检查输入的现金。 但是您需要确保用户没有输入，这意味着他输入了一个数字或名称

private bool Validate()
{

    //Check that the user has entered their car registration
    if(!(CarReg == null || CarReg.isEmpty())) // must NOT be null
    {
        //Check that the user has entered enough money
        if(CurrentBalance >= MinTicketCharge)
        {
            return true;
        }
        else
        {
          System.out.println("You have not entered enough money");
        }
    }
    else
    {
        System.out.println("Please enter your car registration");
    }
    return false;
}

Edit：我应该告诉您，在返回true之后，该方法停止执行。因此，如果您不返回true，这意味着现金的if语句不为true，那么该方法将返回false

通过使用所谓的十进制运算符，可以缩短if语句

这应该是这样的：

return CurrentBalance >= MinTicketCharge ? true : false;

---

在java中，字符串是对象，因此在比较字符串时，应调用.equals方法或.compare方法。CarReg==这是无效代码。我有3个信息供您参考：1；2.CarReg==不正确，请使用CarReg.equals比较字符串类型；3.如果您对错误/异常有疑问，请发布整个错误/异常，并在出现错误/异常的地方标记行。编辑：第四信息：！CarReg.Trim.Equals这将永远不会编译，请将其更改为！CarReg.trim.isEmpty。@Tom感谢您的回复，但是现在当我为“CarParkTicketMachine”创建一个新对象并右键单击它时，我只有“void RequestTick”选项，而没有以前的任何选项，例如SetCarRegistration。正如我之前所说的，我对java非常陌生，所以我不知道能为您提供什么信息来帮助我，所以如果能为我指明正确的方向，我将不胜感激。您能更新您问题中的代码吗？