java 枚举 - 在其他 java 文件中使用时不编译

Question

我正在尝试使用 Java 枚举，但代码未编译。我在整个代码中收到以下错误。

Class, interface, or enum expected

错误

vm@vm:~/Documents/Oops/DesignPatterns/CommandPattern$ javac Kitchen.java

Kitchen.java:1: '.' expected
import HomeApplianceAction;
                      ^
Kitchen.java:1: ';' expected
import HomeApplianceAction;
                           ^
Kitchen.java:3: class, interface, or enum expected
class Kitchen{
      ^
Kitchen.java:5: class, interface, or enum expected
    private Door_Enum kitchen_door;
            ^
Kitchen.java:6: class, interface, or enum expected
    private Fan_Enum exhaust_fan;
            ^
Kitchen.java:8: class, interface, or enum expected
    Kitchen(){
    ^
Kitchen.java:10: class, interface, or enum expected
        this.kitchen_door = Door_Enum.DOOR_SHUT;
        ^
Kitchen.java:11: class, interface, or enum expected
        this.exhaust_fan = Fan_Enum.FAN_SWITCHED_OFF;
        ^
Kitchen.java:12: class, interface, or enum expected
    }
    ^
Kitchen.java:14: class, interface, or enum expected
    public void setKitchenLights(Light_Enum kitchen_light){

如何修复此错误消息？

这是代码片段：

public interface HomeApplianceAction{
}

enum Light_Enum implements HomeApplianceAction{
    LIGHTS_ON,
    LIGHTS_OFF,
    LIGHTS_DIM;
}

enum Door_Enum implements HomeApplianceAction{
    DOOR_OPEN,
    DOOR_SHUT;
}

enum TV_Enum implements HomeApplianceAction{
    TV_POWERED_ON,
    TV_POWERED_OFF,
    TV_STANDBY;
}

enum Computer_Enum implements HomeApplianceAction{
    COMP_POWERED_ON,
    COMP_POWERED_OFF,
    COMP_STANDBY,
    COMP_SLEEP,
    COMP_HIBERNATE;
}

enum Fan_ENUM implements HomeApplianceAction{
    FAN_SWITCHED_OFF,
    FAN_LOW,
    FAN_MEDIUM,
    FAN_HIGH;
}

以上代码放在HomeApplianceAction.java文件中，编译成功。现在我想在 Kitchen.java 文件中使用这些枚举，如下所示：

import HomeApplianceAction;

class Kitchen{
    private Light_Enum kitchen_light;
    private Door_Enum kitchen_door;
    private Fan_Enum exhaust_fan;

    Kitchen(){
        this.kitchen_light = Light_Enum.LIGHTS_OFF;
        this.kitchen_door = Door_Enum.DOOR_SHUT;
        this.exhaust_fan = Fan_Enum.FAN_SWITCHED_OFF;
    }

    public void setKitchenLights(Light_Enum kitchen_light){
        this.kitchen_light = kitchen_light;
    }

    public void setKitchenDoor(Door_Enum kitchen_door){
        this.kitchen_door = kitchen_door;
    }

    public void setKitchenExhaustFan(Fan_Enum exhaust_fan){
        this.exhaust_fan = exhaust_fan;
    }

    public void execute(HomeApplianceAction action){
        if(action instanceof Light_Enum){
            setKitchenLights(action);
        }
        else if(action instanceof Door_Enum){
            setKitchenDoor(action);
        }
        else if(action instanceof Fan_Enum){
            setKitchenExhaustFan(action);
        }
        else{
            System.out.println("Invalid action performed on Kitchen Appliance");
        }
    }
}

Answer 1

您有一个包含多个枚举的文件和一个 public 接口。文件“.java”称为编译单元。每个编译单元只能有一个 public class、接口或枚举。

您可以为每个枚举创建单独的编译单元，或者在接口中实现枚举并像这样访问它：

HomeApplianceAction.Computer_Enum.COMP_HIBERNATE

否则您的枚举只能在界面内看到。

Answer 2

您在同一个文件中有多个 class、接口或枚举，这不是最佳做法。

将它们拆分到不同的文件中，即：

在HomeApplianceAction.java中：

public interface HomeApplianceAction{

}

在LightEnum.java

public enum LightEnum implements HomeApplianceAction{
    LIGHTS_ON,
    LIGHTS_OFF,
    LIGHTS_DIM;
}

请注意，我写的是 LightEnum 而不是 Light_Enum，它遵循 java 代码的命名约定。另请注意 public 修饰符，它允许您在其他包的 classes 中使用此枚举。

您应该考虑为这些 classes 和枚举声明包，也许您需要添加导入语句以便能够从另一个 class 使用它们，如下所示：

import LightEnum;

或

import <yourpackage>.LightEnum;

java 枚举 - 在其他 java 文件中使用时不编译

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