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我已经写ConcurrentSkipListMap了 3 dimensional ，但无法找到一种迭代它的方法。我如何定义iterator相同的。

import java.util.concurrent.ConcurrentSkipListMap;
/**
 * Helper implementation to handle 3 dimensional sorted maps
 */
public class MyCustomIndex {
    private ConcurrentSkipListMap<byte[], ConcurrentSkipListMap<byte[], ConcurrentSkipListMap<byte[], byte[]>>> table;

    public MyCustomIndex() {
        this.table = new ConcurrentSkipListMap<byte[], ConcurrentSkipListMap<byte[], ConcurrentSkipListMap<byte[], byte[]>>>(new CustomComparator); 
    }
    /**
     * 
     * @param K
     * @param F
     * @param Q
     */
    public void put(byte[] K, byte[] F, byte[] Q) {
        ConcurrentSkipListMap<byte[], byte[]> QToDummyValueMap; 
        ConcurrentSkipListMap<byte[], ConcurrentSkipListMap<byte[], byte[]>> FToQMap;

        if( table.containsK(K)) {
            FToQMap = table.get(K);
            if ( FToQMap.containsK(F)) {
                QToDummyValueMap = FToQMap.get(F);
            } else {
                QToDummyValueMap = new ConcurrentSkipListMap<byte[], byte[]>(new CustomComparator); 
            }
        } else {
            QToDummyValueMap = new ConcurrentSkipListMap<byte[], byte[]>(new CustomComparator);
            FToQMap = new ConcurrentSkipListMap<byte[], ConcurrentSkipListMap<byte[], byte[]>>(new CustomComparator);
        }       
        QToDummyValueMap.put(Q, new byte[0]);
        FToQMap.put(F, QToDummyValueMap);
        table.put(K, FToQMap);
    }

    public ConcurrentSkipListMap<byte[], ConcurrentSkipListMap<byte[], ConcurrentSkipListMap<byte[], byte[]>>> gettable() {
        return table;
    }
    public void settable(
            ConcurrentSkipListMap<byte[], ConcurrentSkipListMap<byte[], ConcurrentSkipListMap<byte[], byte[]>>> table) {
        this.table = table;
    }

}
4

1 回答 1

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这是一个嵌套迭代器，它将采用 anIterator<Iterator<T>>并将其转换为Iterator<T>. 还有一些静态方法可以让你Iterator<V>从 s 中生成对象Map<K,V>以及一些高阶的东西（Iterator<Iterator<V>>等等Map<K,Map<K,V>）。

如您在三路测试和 MapMapMap 测试中所见，在更高级别的迭代器上进行迭代的想法Iterator<Iterator<Iterator<T>>>是将其中一个包装在另一个中。

public class NestedIterator<T> implements Iterator<T> {
  // Outer iterator. Goes null when exhausted.
  Iterator<Iterator<T>> i2 = null;
  // Inner iterator. Goes null when exhausted.
  Iterator<T> i1 = null;
  // Next value.
  T next = null;

  // Takes a depth-2 iterator.
  public NestedIterator(Iterator<Iterator<T>> i2) {
    this.i2 = i2;
    // Prime the pump.
    if (i2 != null && i2.hasNext()) {
      i1 = i2.next();
    }
  }

  @Override
  public boolean hasNext() {
    // Is there one waiting?
    if (next == null) {
      // No!
      // i1 will go null if it is exhausted.
      if (i1 == null) {
        // i1 is exhausted! Get a new one from i2.
        if (i2 != null && i2.hasNext()) {
          /// Get next.
          i1 = i2.next();
          // Set i2 null if exhausted.
          if (!i2.hasNext()) {
            // Exhausted.
            i2 = null;
          }
        } else {
          // Exhausted.
          i2 = null;
        }
      }
      // A null i1 now will mean all is over!
      if (i1 != null) {
        if (i1.hasNext()) {
          // get next.
          next = i1.next();
          // Set i1 null if exhausted.
          if (!i1.hasNext()) {
            // Exhausted.
            i1 = null;
          }
        } else {
          // Exhausted.
          i1 = null;
        }
      }
    }
    return next != null;
  }

  @Override
  public T next() {
    T n = next;
    next = null;
    return n;
  }

  @Override
  public void remove() {
    throw new UnsupportedOperationException("Not supported.");
  }

  // Iterating across Maps of Maps of Maps.
  static <K1, K2, K3, V> Iterator<Iterator<Iterator<V>>> iiiV(Map<K1, Map<K2, Map<K3, V>>> i) {
    final Iterator<Map<K2, Map<K3, V>>> iV = iV(i);
    return new Iterator<Iterator<Iterator<V>>>() {
      @Override
      public boolean hasNext() {
        return iV.hasNext();
      }

      @Override
      public Iterator<Iterator<V>> next() {
        return iiV(iV.next());
      }

      @Override
      public void remove() {
        iV.remove();
      }
    };
  }

  // Iterating across Maps of Maps.
  static <K1, K2, V> Iterator<Iterator<V>> iiV(Map<K1, Map<K2, V>> i) {
    final Iterator<Map<K2, V>> iV = iV(i);
    return new Iterator<Iterator<V>>() {
      @Override
      public boolean hasNext() {
        return iV.hasNext();
      }

      @Override
      public Iterator<V> next() {
        return iV(iV.next());
      }

      @Override
      public void remove() {
        iV.remove();
      }
    };
  }

  // Iterating across Map values.
  static <K, V> Iterator<V> iV(final Map<K, V> map) {
    return iV(map.entrySet().iterator());
  }

  // Iterating across Map.Entry Iterators.
  static <K, V> Iterator<V> iV(final Iterator<Map.Entry<K, V>> i) {
    return new Iterator<V>() {
      @Override
      public boolean hasNext() {
        return i.hasNext();
      }

      @Override
      public V next() {
        return i.next().getValue();
      }

      @Override
      public void remove() {
        i.remove();
      }
    };
  }

  // **** TESTING ****
  enum I {
    I1, I2, I3;
  };

  public static void main(String[] args) {
    // Two way test.
    testTwoWay();
    System.out.flush();
    System.err.flush();
    // Three way test.
    testThreeWay();
    System.out.flush();
    System.err.flush();
    // MapMap test
    testMapMap();
    System.out.flush();
    System.err.flush();
    // MapMapMap test
    testMapMapMap();
    System.out.flush();
    System.err.flush();
  }

  private static void testMapMap() {
    Map<String,String> m = new TreeMap<> ();
    m.put("M-1", "V-1");
    m.put("M-2", "V-2");
    Map<String,Map<String,String>> mm = new TreeMap<> ();
    mm.put("MM-1", m);
    mm.put("MM-2", m);
    System.out.println("MapMap");
    Iterator<Iterator<String>> iiV = iiV(mm);
    for (Iterator<String> i = new NestedIterator<>(iiV); i.hasNext();) {
      System.out.print(i.next() + ",");
    }
    System.out.println();
  }

  private static void testMapMapMap() {
    Map<String,String> m = new TreeMap<> ();
    m.put("M-1", "V-1");
    m.put("M-2", "V-2");
    m.put("M-3", "V-3");
    Map<String,Map<String,String>> mm = new TreeMap<> ();
    mm.put("MM-1", m);
    mm.put("MM-2", m);
    Map<String,Map<String,Map<String,String>>> mmm = new TreeMap<> ();
    mmm.put("MMM-1", mm);
    mmm.put("MMM-2", mm);
    System.out.println("MapMapMap");
    Iterator<Iterator<Iterator<String>>> iiiV = iiiV(mmm);
    for (Iterator<String> i = new NestedIterator<>(new NestedIterator<>(iiiV)); i.hasNext();) {
      System.out.print(i.next() + ",");
    }
    System.out.println();
  }

  private static void testThreeWay() {
    // Three way test.
    System.out.println("Three way");
    List<Iterator<I>> lii1 = Arrays.asList(
            EnumSet.allOf(I.class).iterator(),
            EnumSet.allOf(I.class).iterator(),
            EnumSet.allOf(I.class).iterator(),
            EnumSet.allOf(I.class).iterator());
    List<Iterator<I>> lii2 = Arrays.asList(
            EnumSet.allOf(I.class).iterator(),
            EnumSet.allOf(I.class).iterator(),
            EnumSet.allOf(I.class).iterator(),
            EnumSet.allOf(I.class).iterator());
    List<Iterator<I>> lii3 = Arrays.asList(
            EnumSet.allOf(I.class).iterator(),
            EnumSet.allOf(I.class).iterator(),
            EnumSet.allOf(I.class).iterator(),
            EnumSet.allOf(I.class).iterator());
    Iterator<Iterator<Iterator<I>>> liii = Arrays.asList(
            lii1.iterator(),
            lii2.iterator(),
            lii3.iterator()).iterator();
    // Grow a 3-nest.
    // Unroll it.
    for (Iterator<I> ii = new NestedIterator<>(new NestedIterator<>(liii)); ii.hasNext();) {
      I it = ii.next();
      System.out.print(it + ",");
    }
    System.out.println();
  }

  private static void testTwoWay() {
    System.out.println("Two way");
    List<Iterator<I>> lii = Arrays.asList(
            EnumSet.allOf(I.class).iterator(),
            EnumSet.allOf(I.class).iterator(),
            EnumSet.allOf(I.class).iterator());
    for (Iterator<I> ii = new NestedIterator<>(lii.iterator()); ii.hasNext();) {
      I it = ii.next();
      System.out.print(it + ",");
    }
    System.out.println();
  }
}

您的代码现在看起来像这样。请注意，我根本没有对此进行测试，并且我尽可能地使用了Map代替，并且我正在使用Java 7 中的东西来帮助很多。ConcurrentSkipListMap<>

public class MyCustomIndex  implements Iterable<byte[]> {
  private Map<byte[], Map<byte[], Map<byte[], byte[]>>> table;

  public MyCustomIndex() {
    this.table = new ConcurrentSkipListMap<>();
  }

  /**
   * @param K
   * @param F
   * @param Q
   */
  public void put(byte[] K, byte[] F, byte[] Q) {
    Map<byte[], byte[]> QToDummyValueMap;
    Map<byte[], Map<byte[], byte[]>> FToQMap;

    if (table.containsKey(K)) {
      FToQMap = table.get(K);
      if (FToQMap.containsKey(F)) {
        QToDummyValueMap = FToQMap.get(F);
      } else {
        QToDummyValueMap = new ConcurrentSkipListMap<>();
      }
    } else {
      QToDummyValueMap = new ConcurrentSkipListMap<>();
      FToQMap = new ConcurrentSkipListMap<>();
    }
    QToDummyValueMap.put(Q, new byte[0]);
    FToQMap.put(F, QToDummyValueMap);
    table.put(K, FToQMap);
  }

  public Map<byte[], Map<byte[], Map<byte[], byte[]>>> gettable() {
    return table;
  }

  public Iterator<byte[]> iterator () {
    // **** This is what I have been aiming at all along ****
    return new NestedIterator(new NestedIterator<>(NestedIterator.iiiV(table)));
  }

}
于 2013-03-25T15:18:39.470 回答