Feature or bug: unable to override enum method with default implementation of UnsupportedOperationException

I have an application that uses an enum for the options. Some of the options should be able to have some state: an int value or a String value. (I know that in general an enum should only have final attributes, but there are use cases in which the value of the attribute is only known at runtime, and you can't pass arguments for the constructor of an enum at runtime.) I would like the default implementation of the getters and setters for these options to be implemented by throwing a UnsupportedOperationException, like this (part of the original code):

public enum FileTreeOption1 {
  HUMAN_READABLE, DATE, DIRS_ONLY, FILES_ONLY, 
  DEPTH{
    @Override
    public void setIntValue(int value){
      this.intValue = value;
    }
    @Override
    public int getIntValue(){
      return intValue;
    }
  };

  private int intValue;

  public void setIntValue(int value) {
      throw new UnsupportedOperationException("setIntValue not available for " + this.name());
  }
  public int getIntValue() {
      throw new UnsupportedOperationException("getIntValue not available for " + this.name());
  }
}

However, when I try to compile this, I get these error messages (in java 11):

FileTreeOption1.java:7: error: intValue has private access in FileTreeOption1
      this.intValue = value;
          ^
FileTreeOption1.java:11: error: non-static variable intValue cannot be referenced from a static context
      return intValue;
             ^
2 errors

Especially the second error is a strange one: there is no static context.

As a work around, I have managed to get my code working as shown below. But my question is: shouldn't the code above be able to compile?

Work around:

public enum FileTreeOption2 {
  HUMAN_READABLE, DATE, DIRS_ONLY, FILES_ONLY, 
  DEPTH(true);

  private boolean useIntValue;
  private int intValue;

  FileTreeOption2( boolean useIntValue){
    this.useIntValue = useIntValue;
  }
  FileTreeOption2(){}


  public void setIntValue(int value) {
    if(useIntValue){
      this.intValue = value;
    } else {
      throw new UnsupportedOperationException("setIntValue not available for " + this.name());
    }
  }
  public int getIntValue() {
    if(useIntValue){
      return this.intValue;
    } else {
      throw new UnsupportedOperationException("getIntValue not available for " + this.name());
    }
  }
}

Thanks to the help of Nikolai, I have just found out that not only can you override methods in an enum constant, but you can add variables to them too. So this one actually works:

public enum FileTreeOption1 {
  HUMAN_READABLE, DATE, DIRS_ONLY, FILES_ONLY, 
  DEPTH{
	 private int intValue; // attribute only available to DEPTH
    @Override
    public void setIntValue(int value){
      this.intValue = value;
    }
    @Override
    public int getIntValue(){
      return intValue;
    }
  };

  public void setIntValue(int value) {
      throw new UnsupportedOperationException("setIntValue not available for " + this.name());
  }
  public int getIntValue() {
      throw new UnsupportedOperationException("getIntValue not available for " + this.name());
  }
  
  public static void main(String args[]){
	  FileTreeOption1 option = FileTreeOption1.DEPTH;
	  option.setIntValue(3);
	  System.out.println(option.getIntValue());  // 3
	  option = FileTreeOption1.DATE;
	  System.out.println(option.getIntValue());  // UnsupportedOperationException
  }
}

</details>



# 答案2
**得分**: 1

你必须将 `intValue` 的可见性从 `private` 更改为 `protected`，以使代码能够编译。

<details>
<summary>英文:</summary>

You must change `intValue` visibility from `private` to `protected` to make the code compile

</details>



# 答案3
**得分**: 1

以下是翻译好的部分：

```java
public enum FileTreeOption1 {
  HUMAN_READABLE, DATE, DIRS_ONLY, FILES_ONLY, 
  DEPTH{
    @Override
    public void setIntValue(int value){
      throw new UnsupportedOperationException();
    }
    @Override
    public int getIntValue(){
      return 1;
    }
  } ;

  private int intValue;

  public void setIntValue(int value) {
      this.intValue = value;
  }
  public int getIntValue() {
      return intValue;
  }
}

public enum FileTreeOption1 {
  HUMAN_READABLE, DATE, DIRS_ONLY, FILES_ONLY, 
  DEPTH{
    @Override
    public void setIntValue(int value){
      throw new UnsupportedOperationException();
    }
    @Override
    public int getIntValue(){
      return 1;
    }
  } ;

  private int intValue;


  public void setIntValue(int value) {
      this.intValue = value;
  }
  public int getIntValue() {
      return intValue;
  }
}

答案4

得分: 0

错误：<strike>
对于你的问题的简短回答是 - 不可以。这段代码不应该能够编译。

解释：

首先，枚举是无法被扩展的。当你尝试定义你的 DEPTH{ 时，实际上你正在创建一个匿名类来扩展你的枚举。在Java中，这是不可能的。这也是第一个错误的原因：private int intValue; 是私有字段 - 因此在子类中是不可见的。
</strike>

这段代码无法编译，因为 private int intValue; 使用了 private 修饰符，而当你创建你的 DEPTH{ 时，你无法在那里访问 private 字段。只能使用 public 或者 protected。

静态上下文 - Java 的 enums 默认是 public static final 的（你可以在Eclipse的大纲窗格中看到这一点）。