为什么我不能在arraylist中使用getFixed方法？我怎样才能使它工作？

 import java.util.*;
 public class MainFile{
 public static void main(String[] args){
    ArrayList<TypeExpences> listOfTypes = new ArrayList<TypeExpences>();
    Water waterExp = new Water(0, "fafasd", 10, "cubic meters", 2, 1);
    listOfTypes.add(waterExp);
    System.out.println((listOfTypes.get(0)).getFixed());
    }
}

public class Water extends UseExpences{
    int pricePer2;  
    public Water(int kod, String descr, int fixed, String unit, int 
     pricePer, int pricePer2){
    super(kod, descr, fixed, unit, pricePer);
    this.pricePer2 = pricePer2;
    }
   public int getFixed(){
   return super.getFixedPrice(fixedPrice);
   }
}

public class UseExpences extends TypeExpences{
    protected int fixedPrice;
    protected String unitOfMeasurement;
    protected int pricePerMeasurementUnit;

    public UseExpences(int kod, String descr, int fixed, String unit, int 
     pricePer){
        super(kod, descr);
        fixedPrice = fixed;
        unitOfMeasurement = unit;
        pricePerMeasurementUnit = pricePer;
    }

    public int getFixedPrice(int fixedPrice){
        return fixedPrice;
    }
}

public class TypeExpences {
    protected int code;
    protected String description;
    public TypeExpences(int kod, String descr){
        code = kod;
        description = descr;
    }
    protected int getCode(int code){
        return code;
    }
    protected String getDescription(String description){
        return description;
    }
}

Error:

错误：

C:\Users\laptopara\Desktop\ask>javac MainFile.java
MainFile.java:39: error: cannot find symbol
System.out.println((listOfTypes.get(0)).getFixed());
                                       ^        
symbol:   method getFixed()
location: class TypeExpences
1 error

If I do System.out.println(waterExp.getFixed()); it works.

如果我做System.out.println（waterExp.getFixed（））;有用。

How can I make it work with System.out.println((listOfTypes.get(0)).getFixed());?

如何使它与System.out.println一起使用（（listOfTypes.get（0））。getFixed（））;?

1 个解决方案

#1

Ah yea I think your problem is, that you use polymorphic programming... You have a object ArrayList<TypeExpences> listOfTypes, an ArrayList which stores objects of class TypeExpences. Thanks to polymorphic programming it's possible to store also objects of sub-classes of TypeExpences like Water.

啊啊，我认为你的问题是，你使用多态编程...你有一个对象ArrayList listOfTypes，一个存储TypeExpences类对象的ArrayList。多亏了多态编程，它还可以存储像Water这样的TypeExpences子类的对象。

Your problem is now, that you can't use methods which are declared in the sub-class Water! You can only use methods which are already declared in your base-class TypeExpences and I guess the method public int getFixed() isn't declared.

你现在的问题是，你不能使用在子类Water中声明的方法！您只能使用已经在基类TypeExpences中声明的方法，我想方法public int getFixed（）没有声明。

Change your code to this...

将您的代码更改为此...

ArrayList <Water> listOfTypes = new ArrayList<Water>();

...to fix this issue. Alternate you can implement the method public int getFixed() in base-class TypeExpences and override it in the sub-class.

...解决这个问题。或者，您可以在基类TypeExpences中实现方法public int getFixed（）并在子类中覆盖它。

Maybe also take a look on this tutorial or something like that...

也许还看看这个教程或类似的东西......

EDIT

编辑

You can use an interface like this

你可以使用这样的界面

public interface AllMyObjects
{
    public abstract int getFixed();
}

Now implement this interface in each class you use like this:

现在在您使用的每个类中实现此接口，如下所示：

public class Water implements AllMyObjects
{
    ...
    @Override public int getFixed()
    {
        return super.getFixedPrice(fixedPrice);
    }
}

...

public class Phone implements AllMyObjects
{
    @Override public int getFixed()
    {
        ...
    }
}

After this change your array list like this:

在此更改后，您的数组列表如下所示：

ArrayList <AllMyObjects> listOfTypes = new ArrayList<>();

Now its should work if not, write a comment...

现在它应该工作，如果没有，写评论......

#1