Java中的多级地图

您可以使用您的特定密钥:

You can use your specific key:

class MyKey {
    Double beta;
    Double yaw;
    int minute;

    public int hashCode() {
        /* Returns hash code from a combination of hash of the key members. */
    }

    @Override
    public boolean equals(Object obj) {
        /* Returns true if obj is a MyKey with same members. */
    }
}

然后简单地:

data.put(myKey, obj);

这样，多级检查"全部隐藏在 MyKey.equals()中.它可以使客户端代码保持整洁，并且关键的复杂性放在安全的位置.

This way the "multi-level checks" are all hidden in MyKey.equals(). It keeps the client code clean and the key complexity is in a safe place.

如果最重要的是，您希望能够从双 beta 到您的对象建立一个映射，那么我仍然会像这样保持事物的平面.

If on top of this, you want to be able to have a map from your double beta to your objects, then I would still keep the thing planar like that.

您真正想要的是为数据提供多个索引"，例如在数据库中，因此您可以查询具有相同"beta"或"yaw"的对象.为此，最好的方法是使用多个Map(实际上是Multimap)，每个索引"使用一个.

What you actually want is to have multiple "indexes" for your data, like in a database, so you can query for objects with same "beta" or "yaw". For that the best way is to use several Map (actually Multimap), one for each of your "indexes".

使用番石榴的Multimap:

ListMultimap<Double, Data> mapForBeta;
ListMultimap<Double, Data> mapForYaw;

您可以将所有多图和 Map< MyKey，Data> 放在特定的类中.实际上，最好的方法是继承 Map< MyKey，Data> :

You can put all the multimap and the Map<MyKey, Data> in your a specific class. Actually the best way would be to subclass Map<MyKey, Data>:

public class MyMap extends HashMap<MyKey, Data> {

    ListMultimap<Double, Data> mapForBeta;
    ListMultimap<Double, Data> mapForYaw;


    public Data put(MyKey key, Data value) {
        super.put(key, value);
        mapForBeta.add(key.beta, value);
        mapForYaw.add(key.yaw, value);
    };

    public List<Data> getFromBeta(Double beta) {
        return mapForBeta.get(beta);
    }

    public List<Data> getFromYaw(Double yaw) {
        return mapForYaw.get(yaw);
    }
}

具有更好解决方案的新

实际上，这让我开始思考，我意识到您的地图默认值确实存在问题，这就是为什么您的代码有点混乱的原因.

New Edit with better solution:

Actually, it got me thinking, and I realized that you are really having a problem with default values for your maps, and that's why your code is a bit messy.

您可以使用生成器来创建基础地图的默认地图来解决此问题:

You can solve this with a Default Map using a generator to create underlying maps:

public class DefaultMap<K, V> extends TreeMap<K, V> {

    static abstract class Generator<V>{
        abstract V create();
    }

    final Generator<V> generator;


    DefaultMap(Generator<V> generator) {
        this.generator = generator;
    }

    @Override
    public V get(Object key) {
        V val = super.get(key);
        if (val == null) {
            val = generator.create();

            put((K)key, val);
        }

        return val;
    }
}

现在，您可以使用实用程序树类来存储所有数据:

Now you can have your utility tree class to store all your data :

public class MyTree {
  private final Map<Double, Map<Double, Map<Integer, Data>>> data;

  public MyTree() {
    data = new DefaultMap<>(new Generator<Map<Double, Map<Integer, Data>>>() {
      @Override
      Map<Double, Map<Integer, Data>> create() {
        return new DefaultMap<>(new Generator<Map<Integer, Data>>() {

          @Override
          Map<Integer, Data> create() {
            return new TreeMap<>();
          }

        });
      }
    });
  }

  void add(MyKey d, Data obj) {
    data.get(d.beta).get(d.yaw).put(d.minute, obj);
  }
}

现在，您可以使用data.get(beta).get(yaw)访问数据，并且没有意大利面条式代码来存储您的值.

Now you can access your data with data.get(beta).get(yaw) and you don't have spaghetti code to store your values.