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Infinispan Commons

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package org.infinispan.commons.util;

import java.util.Collection;
import java.util.Map;
import java.util.Objects;
import java.util.Set;

/**
 * Similar to the JDK's AbstractMap, this provides common functionality for custom map implementations.  Unlike JDK's
 * AbstractMap, there is no support for null keys.
 *
 * @author Manik Surtani
 * @since 4.0
 */
public abstract class AbstractMap implements Map {
   // views
   protected transient Set> entrySet = null;
   protected transient Set keySet = null;
   protected transient Collection values = null;

   @Override
   public int hashCode() {
      int h = 0;
      for (Entry kvEntry : entrySet()) h += kvEntry.hashCode();
      return h;
   }

   // The normal bit spreader...
   protected static int hash(Object key) {
      int h = key.hashCode();
      h ^= (h >>> 20) ^ (h >>> 12);
      return h ^ (h >>> 7) ^ (h >>> 4);
   }

   protected static boolean eq(Object o1, Object o2) {
      return Objects.equals(o1, o2);
   }

   protected static void assertKeyNotNull(Object key) {
      if (key == null) throw new NullPointerException("Null keys are not supported!");
   }

   protected static class SimpleEntry implements Map.Entry {
      private final K key;
      private V value;

      SimpleEntry(K key, V value) {
         this.key = key;
         this.value = value;
      }

      @Override
      public K getKey() {
         return key;
      }

      @Override
      public V getValue() {
         return value;
      }

      @Override
      public V setValue(V value) {
         V old = this.value;
         this.value = value;
         return old;
      }

      public boolean equals(Object o) {
         if (this == o)
            return true;

         if (!(o instanceof Map.Entry))
            return false;
         Map.Entry e = (Map.Entry) o;
         return eq(key, e.getKey()) && eq(value, e.getValue());
      }

      public int hashCode() {
         return hash(key) ^
               (value == null ? 0 : hash(value));
      }

      public String toString() {
         return getKey() + "=" + getValue();
      }
   }
}