Enum类如何扩展另一个外部库类？

Question

现在，我有一个现有的类，我想将其重构为一个Enum。该类当前扩展了另一个类，该类来自外部库。我仍然想从扩展类的某些逻辑中受益，同时希望进行重构。应该怎么做？

在Java中，一个enum类不能扩展另一个类，而可以实现interface。或将其重构为枚举的想法已经是错误的吗？让我在下面的示例代码中展示它。

假设一个现有的类Existing正在扩展另一个类Parent，并且Parent类来自外部库，它不是接口。

class Existing extends Parent{
    public static final Existing A = new Existing(...);
    ....
    public static final Existing Z = new Existing(...);

    public Existing(Srting attr1, String attr1){
        super(attr1, attr2);
    }

    public Existing(String attr1){
       super(attr1);
    }
}

这个想法是让那些静态的final字段成为Enums，例如：

enum NewDesign{
     A(attr1, attr2),
     B(attr1),
     C(attr1, attr2)
     //...;
     //constructor etc.
     //...
}

并可能在需要时添加新的额外属性，如下所示：

enum NewDesign{
  A(attr1, attr2, newAttr),
  B(attr1, newAttr),
  C(attr1, attr2, newAttr),
  //...
  //constructor etc.
  //...
}

Answer 1

If the main change that you need is to create an enum to get rid of static final fields, the easiest way to go about it is to create a different, enum type with initialized instances:

enum ExistingEnum {
    A("attr1", "attr2"), 
    Z("attr");

    private final Existing existing;

    ExistingEnum(String attr1) {
        this.existing = new Existing(attr1);
    }

    ExistingEnum(String attr1, String attr2) {
        this.existing = new Existing(attr1, attr2);
    }

    public Existing getExisting() {
        return existing;
    }
}

Depending on how you're using your Existing class currently, you may still be able to change it to an enum. In the following example, I expose an instance of Parent on the enum, assuming code using Existing can be changed to call Existing.A.getParent().parentMethod()...

enum Existing {
    A("attr1", "attr2"),

    Z("attr");

    private final Parent existing;

    Existing(String attr1) {
        this.existing = new ParentImpl(attr1);
    }

    Existing(String attr1, String attr2) {
        this.existing = new ParentImpl(attr1, attr2);
    }

    public Parent getParent() {
        return existing;
    }

    // only needed if logic is overridden
    private static class ParentImpl extends Parent {
        public static final Existing A = "";
        public static final Existing Z = "";

        public ParentImpl(String attr1, String attr2) {
            super(attr1, attr2);
        }

        public ParentImpl(String attr1) {
            super(attr1);
        }
    }
}