Java中的C-like枚举

Question

我试图在C++中为以下方便找到Java等价物:

enum {
  ANIMAL_CAT = 0,
  ANIMAL_RAT,
  ANIMAL_BAT, ...
  NUM_ANIMALS
};

Animal animals[NUM_ANIMALS];

animals[ANIMAL_CAT].mNumLegs = 4;
animals[ANIMAL_RAT].mNumLegs = 4; ...

我知道这不是世界上最漂亮的东西,但我可以在枚举中的任何地方添加一个新的ANIMAL_xxx,并且所有以下条目都将自动调整.在Java中有一种干净的方法吗？

---

感谢您的回复,但我可能提到了比我想象的更简单.

我正在开发一个游戏,那里有一个物理,AI引擎等等.我正在尝试整合我需要的每种类型实体的所有信息(有些只有物理表现,有些同时有物理和AI,等...),这样我就可以轻松添加/修改类型(因此,动物是一个不好的例子,因为我可能需要岩石,植物等......).

我正在使用类来存储类型信息,而其他类依赖于该类来查找属性(维度,位图索引,hasAi等等).最后,我正在尝试清理类似的东西以下,同时允许我轻松添加新类型:

class UnitTypeInfo {
  UnitTypeInfo() {
    mTypes = new TypeInfo[NUM_TYPES];

    // and allocate...

    // initialize TypeInfos here
    mTypes[TYPE_CAT].mType = TYPE_CAT;
    mTypes[TYPE_CAT].mMass = 10.0f;
    mTypes[TYPE_CAT] ...

    mTypes[TYPE_ROCK].mType = TYPE_ROCK;
    ...
  }

  public class TypeInfo {
    public int mType;
    public int mRawResourceHandle;
    public float mMass;
    public Vector2d mDimensions;
    public float mHealth;
    public boolean mHasAi;
    ...
  }

  public static final int TYPE_CAT = 0;
  public static final int TYPE_ROCK = 1;
  public static final int TYPE_TREE = 2; ...
  public static final int NUM_TYPES = ???; // the last TYPE_ + 1

  public TypeInfo mTypes[];
}

现在,这似乎是某种XML实现可能是"正确"的事情,但我不确定如何做到这一点(Java新手).无论如何,其他类可以很容易地使用unitTypeInfo.mTypes [UnitTypeInfo.TYPE_CAT] .mMass(实例化)来查找cat的质量.但是,如果我想在TYPE_CAT定义下面添加一个TYPE_DOG,我必须更新它下面的所有内容(懒惰,我知道,但让我们看看还有更多类型.)

Enums在C++中为这个问题提供了一个简单的解决方案,但是在Java中,我现在能够解决的最简单的解决方案需要:unitTypeInfo.mTypes [UnitTypeInfo.mTypeEnum.TYPE_CAT.ordinal()].mMass - 而我想这个并没有比我已经糟糕的解决方案更糟糕,它确实增加了更多的间接和实际的方法调用(对于大多数来源似乎不鼓励的方法).

还有一件事是我希望能够调用一个开关(类型),这也可能限制了可能的解决方案.

无论如何,我开始意识到必须有一个更好的解决方案来解决这个问题.有什么建议？

Answer 1

"经典"java总是使用"static final int ANIMAL_CAT = 0;" 在这种情况下.

JDK 1.5引入了"类型安全枚举":

http://www.javapractices.com/topic/TopicAction.do?Id=1

你现在可以这样做(一种非常普遍的做法):

enum Quark {
    /*
    * These are called "enum constants".
    * An enum type has no instances other than those defined by its
    * enum constants. They are implicitly "public static final".
    * Each enum constant corresponds to a call to a constructor.
    * When no args follow an enum constant, then the no-argument constructor
    * is used to create the corresponding object.
    */
    UP,
    DOWN,
    CHARM,
    STRANGE,
    BOTTOM,
    TOP
  }

或者你可以这样做:

/**
  * Example 2 - adding a constructor to an enum.
  *
  * If no constructor is added, then the usual default constructor
  * is created by the system, and declarations of the
  * enum constants will correspond to calling this default constructor.
  */
  public enum Lepton {
    //each constant implicity calls a constructor :
    ELECTRON(-1, 1.0E-31),
    NEUTRINO(0, 0.0);

    /* 
    * This constructor is private.
    * Legal to declare a non-private constructor, but not legal
    * to use such a constructor outside the enum.
    * Can never use "new" with any enum, even inside the enum 
    * class itself.
    */
    private Lepton(int aCharge, double aMass){
      //cannot call super ctor here
      //calls to "this" ctors allowed
      fCharge = aCharge;
      fMass = aMass;
    }
    final int getCharge() {
      return fCharge;
    }
    final double getMass() {
      return fMass;
    }
    private final int fCharge;
    private final double fMass;
  }

这是官方文件:

http://docs.oracle.com/javase/1.5.0/docs/guide/language/enums.html

Answer 2

为什么不这么简单:

public enum Animal {
    CAT(4), RAT(4), BAT(4), CHICKEN(2), ..., ANT(6), SPIDER(8);

    // A simple attribute, like any other java class.
    // Final to ensure it will never change.
    private final int legs;

    // Note that this constructor is private.
    private Animal(int legs) {
        this.legs = legs;
    }

    // A method, like any other class.
    public int getLegs() {
        return legs;
    }
}

要使用它:

// How to get all the animals in the enum.
Animal[] animals = Animal.values();

// How to get the number of animals.
int numAnimals = animals.length;

// How to get the number of legs of some animal.
int howManyLegsHaveTheAnt = Animal.ANT.getLegs();
int howManyLegsHaveTheFirstAnimal = animals[0].getLegs();

// How to get the name of a given animal.
String theFirstAnimalName = animals[0].name(); // Will return "CAT".

// How to get the position in the enum of some animal.
int antPositionInTheEnum = Animal.ANT.ordinal();

// How to get an animal given its name.
Animal rat = Enum.valueOf(Animal.class, "RAT");
Animal someAnimal = Enum.valueOf(Animal.class, animalName);