ClassCastException 类型转换异常 class.Accommodation 无法转换为 class.Attraction。

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英文:

ClassCastException class.Accomodation cannot be cast to class.Attraction

问题

这是我的模型：

public class Accomodation {
    ...
}

以及

public class Attraction extends Accomodation {
    ...
    private String openingTime;
}

我在我的 Controller 类中有这个方法：

protected Accomodation getAccomodationByFormData(CrudView crudView) {
    Accomodation accomodation = new Accomodation();
    // 设置器方法
    return accomodation;
}

该方法在 AttractionController 中使用（该类扩展了之前的 Controller）：

@Override
protected Accomodation getAccomodationByFormData(CrudView crudView) {
    Attraction attraction = (Attraction) super.getAccomodationByFormData(crudAttractionView);
    attraction.setOpeningTime(getOpeningTimeWithFormData()); 
    return attraction;
}

在这个 AttractionController 的另一个地方，我有：

...
Attraction attraction = (Attraction) getAccomodationByFormData(crudAttractionView); // 抛出 ClassCastException
...

但是这给了我以下错误：

> 异常线程 "JavaFX Application Thread" java.lang.ClassCastException: class models.Accomodation cannot be cast to class models.Attraction (models.Accomodation and models.Attraction are in unnamed module of loader 'app')
    at controllers.CrudAttractionController.getAccomodationByFormData(CrudAttractionController.java:302)
    at controllers.CrudAttractionController.lambda$buttonConfermaClicked$4(CrudAttractionController.java:143)
    ...

（注：请注意 CrudAttractionView 类扩展了 CrudView）

  • 如何修复？

编辑

Attraction

public class Attraction extends Accomodation {
    private String openingTime;

    public Attraction() {

    }

    public Attraction(Accomodation accomodation) {
        super(accomodation);
    }

    // 获取器和设置器方法
}

Accomodation

public class Accomodation implements Serializable {
    protected String id;
    protected String name;
    protected Integer avarageRating;
    protected Integer avaragePrice;
    protected String phoneNumber;
    protected Address address;
    protected Point point;
    protected List<Review> reviews;
    protected Long totalReviews;
    protected Long totalRating;
    protected List<String> images;
    protected boolean hasCertificateOfExcellence;
    protected String addedDate;
    protected String lastModificationDate;

    public Accomodation() {

    }

    public Accomodation(Accomodation accomodation) {
    }

    // 获取器和设置器方法
}
英文:

These are my mondels:

public class Accomodation {
    ...
}

and

public class Attraction extends Accomodation {
    ... 
    private String openingTime;
}

I have this method in my Controller class:

protected Accomodation getAccomodationByFormData(CrudView crudView) {
        Accomodation accomodation = new Accomodation();
        // setters
        return accomodation;
    }

which is used within AttractionController (which extends previous Controller):

@Override
    protected Accomodation getAccomodationByFormData(CrudView crudView) {
        Attraction attraction = (Attraction) super.getAccomodationByFormData(crudAttractionView);
        attraction.setOpeningTime(getOpeningTimeWithFormData()); 
        return attraction;
    }

in another point of this AttractionController I have:

...
Attraction attraction = (Attraction) getAccomodationByFormData(crudAttractionView); // throws ClassCastException
...

But this is giving me:

> Exception in thread "JavaFX Application Thread" java.lang.ClassCastException: class models.Accomodation cannot be cast to class models.Attraction (models.Accomodation and models.Attraction are in unnamed module of loader 'app')
at controllers.CrudAttractionController.getAccomodationByFormData(CrudAttractionController.java:302)
at controllers.CrudAttractionController.lambda$buttonConfermaClicked$4(CrudAttractionController.java:143)
at javafx.base/com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(CompositeEventHandler.java:86)
at javafx.base/com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:238)
at javafx.base/com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:191)
at javafx.base/com.sun.javafx.event.CompositeEventDispatcher.dispatchBubblingEvent(CompositeEventDispatcher.java:59)
at javafx.base/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:58)
at javafx.base/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at javafx.base/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
at javafx.base/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at javafx.base/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
at javafx.base/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at javafx.base/com.sun.javafx.event.EventUtil.fireEventImpl(EventUtil.java:74)
at javafx.base/com.sun.javafx.event.EventUtil.fireEvent(EventUtil.java:49)
at javafx.base/javafx.event.Event.fireEvent(Event.java:198)
at javafx.graphics/javafx.scene.Node.fireEvent(Node.java:8879)
at javafx.controls/javafx.scene.control.Button.fire(Button.java:200)
at javafx.controls/com.sun.javafx.scene.control.behavior.ButtonBehavior.mouseReleased(ButtonBehavior.java:206)
at javafx.controls/com.sun.javafx.scene.control.inputmap.InputMap.handle(InputMap.java:274)
at javafx.base/com.sun.javafx.event.CompositeEventHandler$NormalEventHandlerRecord.handleBubblingEvent(CompositeEventHandler.java:218)
at javafx.base/com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(CompositeEventHandler.java:80)
at javafx.base/com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:238)
at javafx.base/com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:191)
at javafx.base/com.sun.javafx.event.CompositeEventDispatcher.dispatchBubblingEvent(CompositeEventDispatcher.java:59)
at javafx.base/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:58)
at javafx.base/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at javafx.base/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
at javafx.base/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at javafx.base/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
at javafx.base/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at javafx.base/com.sun.javafx.event.EventUtil.fireEventImpl(EventUtil.java:74)
at javafx.base/com.sun.javafx.event.EventUtil.fireEvent(EventUtil.java:54)
at javafx.base/javafx.event.Event.fireEvent(Event.java:198)
at javafx.graphics/javafx.scene.Scene$MouseHandler.process(Scene.java:3851)
at javafx.graphics/javafx.scene.Scene$MouseHandler.access$1200(Scene.java:3579)
at javafx.graphics/javafx.scene.Scene.processMouseEvent(Scene.java:1849)
at javafx.graphics/javafx.scene.Scene$ScenePeerListener.mouseEvent(Scene.java:2588)
at javafx.graphics/com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:397)
at javafx.graphics/com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:295)
at java.base/java.security.AccessController.doPrivileged(Native Method)
at javafx.graphics/com.sun.javafx.tk.quantum.GlassViewEventHandler.lambda$handleMouseEvent$2(GlassViewEventHandler.java:434)
at javafx.graphics/com.sun.javafx.tk.quantum.QuantumToolkit.runWithoutRenderLock(QuantumToolkit.java:390)
at javafx.graphics/com.sun.javafx.tk.quantum.GlassViewEventHandler.handleMouseEvent(GlassViewEventHandler.java:433)
at javafx.graphics/com.sun.glass.ui.View.handleMouseEvent(View.java:556)
at javafx.graphics/com.sun.glass.ui.View.notifyMouse(View.java:942)
at javafx.graphics/com.sun.glass.ui.gtk.GtkApplication._runLoop(Native Method)
at javafx.graphics/com.sun.glass.ui.gtk.GtkApplication.lambda$runLoop$11(GtkApplication.java:277)
at java.base/java.lang.Thread.run(Thread.java:834)

(Ps. Note that CrudAttractionView class extends CrudView)

  • How can I fix?

EDIT

Attraction

public class Attraction extends Accomodation {
    private String openingTime;

    public Attraction() {

    }

    public Attraction(Accomodation accomodation) {
        super(accomodation);
    }

    // getters and setters
}

Accomodation

public class Accomodation implements Serializable {
    protected String id;
    protected String name;
    protected Integer avarageRating;
    protected Integer avaragePrice;
    protected String phoneNumber;
    protected Address address;
    protected Point point;
    protected List&lt;Review&gt; reviews;
    protected Long totalReviews;
    protected Long totalRating;
    protected List&lt;String&gt; images;
    protected boolean hasCertificateOfExcellence;
    protected String addedDate;
    protected String lastModificationDate;

    public Accomodation() {

    }

    public Accomodation(Accomodation accomodation) {
    }

    // getters and setters
}

答案1

得分: 2

所有的 `Attraction` 都是 `Accomodation`，但并非所有的 `Accomodation` 都是 `Attraction`。

这意味着你不能安全地执行：

    Attraction attraction = (Attraction) super.getAccomodationByFormData(crudAttractionView);

即使你在一个 `AttractionController` 中（Java 不会根据你控制器的名称更改 super.getAccomodation 的返回类型）。

一个不需要任何框架的解决方案是这样的：

    Accomodation accomodation = super.getAccomodationByFormData(crudAttractionView);
    Attraction attraction = new Attraction(accomodation);
    attraction.setOpeningTime(getOpeningTimeWithFormData())

你只需要确保你有一个接受 `Accomodation` 的 `Attraction` 构造函数，并将其字段复制到你的景点。

类似于：

    public Attraction(Accomodation accomodation){
      attraction.setX(accomodation.getX())
      ...
    }

或者只是调用 `super(accomodation)`，并在 `Accomodation` 中有一个构造函数，可以将一个 `Accomodation` 复制到一个新的实例中（这样你将能够在所有未来的扩展类中使用该构造函数）

现在，确保你的 `accomodation` 实际上是一个 `Attraction`，然后进行类型转换。

在一个更简洁的例子中，以下是代码示例：

```java
import java.io.Serializable;

class Attraction extends Accomodation {

    public Attraction() {

    }

    public Attraction(Accomodation accomodation) {
        super(accomodation); // 让超类进行简单映射
    }

    // 获取器和设置器

    public void setOpeningTime(String test){
        //
    }

    protected Accomodation getAccomodationByFormData() {
        Accomodation accomodation= new Accomodation();//super.getAccomodationByFormData(crudAttractionView);
        Attraction attraction = new Attraction(accomodation); // 通过构造函数将我们的 accomodation 转换
        attraction.setOpeningTime("..."); // 设置开放时间
        return attraction;
    }
}

class Accomodation implements Serializable {
    protected String id;
    protected String name;
    protected Integer avarageRating;
    protected Integer avaragePrice;
    protected String phoneNumber;
    protected Long totalReviews;
    protected Long totalRating;
    protected boolean hasCertificateOfExcellence;
    protected String addedDate;
    protected String lastModificationDate;

    public Accomodation(Accomodation accomodation) {
        this.id = accomodation.id;
        this.name = accomodation.name;
        this.avarageRating = accomodation.avarageRating;
        this.avaragePrice = accomodation.avaragePrice;
        this.phoneNumber = accomodation.phoneNumber;
        this.totalReviews = accomodation.totalReviews;
        this.totalRating = accomodation.totalRating;
        this.hasCertificateOfExcellence = accomodation.hasCertificateOfExcellence;
        this.addedDate = accomodation.addedDate;
        this.lastModificationDate = accomodation.lastModificationDate;
    }

    public Accomodation() {

    }

    // 获取器和设置器
}
英文:

All Attraction are Accomodation, but not all Accomodation are Attraction.

It means you cannot do safely :

Attraction attraction = (Attraction) super.getAccomodationByFormData(crudAttractionView);

Even if you are in a AttractionController (java doesn't change the return type of super.getAccomadation based on your controller's name).

One solution without the need of any Framework would be to do something like :

Accomodation accomodation = super.getAccomodationByFormData(crudAttractionView);
Attraction attraction = new Attraction(accomodation);
attraction.setOpeningTime(getOpeningTimeWithFormData())

You just have to make sure you have an Attraction Constructor that will take that Accomodation and copy it fields to your attraction.

Something like :

public Attraction(Accomodation accomodation){
attraction.setX(accomodation.getX())
...
}

Or just calling super(accomodation) and having a Constructor in Accomodation that will be able to copy an Accomodation into a new one (so you'll be able to use that Constructor in all future extending classes)

Now, you ensure your accomodation is effectively an Attraction, then you cast it.

In a more concise example, here is what it would looks like

import java.io.Serializable;
class Attraction extends Accomodation {
public Attraction() {
}
public Attraction(Accomodation accomodation) {
super(accomodation); // we let super do the simple mapping
}
// getters and setters
public void setOpeningTime(String test){
//
}
protected Accomodation getAccomodationByFormData() {
Accomodation accomodation= new Accomodation();//super.getAccomodationByFormData(crudAttractionView);
Attraction attraction = new Attraction(accomodation); // we convert our accomodation thanks to our constructor
attraction.setOpeningTime(&quot;...&quot;);
return attraction;
}
}
class Accomodation implements Serializable {
protected String id;
protected String name;
protected Integer avarageRating;
protected Integer avaragePrice;
protected String phoneNumber;
protected Long totalReviews;
protected Long totalRating;
protected boolean hasCertificateOfExcellence;
protected String addedDate;
protected String lastModificationDate;
public Accomodation(Accomodation accomodation) {
this.id = accomodation.id;
this.name = accomodation.name;
this.avarageRating = accomodation.avarageRating;
this.avaragePrice = accomodation.avaragePrice;
this.phoneNumber = accomodation.phoneNumber;
this.totalReviews = accomodation.totalReviews;
this.totalRating = accomodation.totalRating;
this.hasCertificateOfExcellence = accomodation.hasCertificateOfExcellence;
this.addedDate = accomodation.addedDate;
this.lastModificationDate = accomodation.lastModificationDate;
}
public Accomodation() {
}
// getters and setters
}

huangapple
  • 本文由 发表于 2020年10月1日 18:12:30
  • 转载请务必保留本文链接：https://go.coder-hub.com/64153266.html
  • classcastexception
  • java
  • polymorphism
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