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    • com.google.common.collect.RegularImmutableMultiset Maven / Gradle / Ivy

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    This artifact provides a single jar that contains all classes required to use remote Jakarta Enterprise Beans and Jakarta Messaging, including all dependencies. It is intended for use by those not using maven, maven users should just import the Jakarta Enterprise Beans and Jakarta Messaging BOM's instead (shaded JAR's cause lots of problems with maven, as it is very easy to inadvertently end up with different versions on classes on the class path).

    There is a newer version: 35.0.0.Final
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    /*
 * Copyright (C) 2011 The Guava Authors
 *
 * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
 * in compliance with the License. You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software distributed under the License
 * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
 * or implied. See the License for the specific language governing permissions and limitations under
 * the License.
 */

package com.google.common.collect;

import static com.google.common.base.Preconditions.checkNotNull;

import com.google.common.annotations.GwtCompatible;
import com.google.common.annotations.VisibleForTesting;
import com.google.common.base.Objects;
import com.google.common.collect.Multisets.ImmutableEntry;
import com.google.common.primitives.Ints;
import com.google.errorprone.annotations.concurrent.LazyInit;
import java.util.Arrays;
import java.util.Collection;
import org.checkerframework.checker.nullness.compatqual.NullableDecl;

/**
 * Implementation of {@link ImmutableMultiset} with zero or more elements.
 *
 * @author Jared Levy
 * @author Louis Wasserman
 */
@GwtCompatible(emulated = true, serializable = true)
@SuppressWarnings("serial") // uses writeReplace(), not default serialization
class RegularImmutableMultiset extends ImmutableMultiset {
  static final ImmutableMultiset EMPTY = create(ImmutableList.>of());

  static  ImmutableMultiset create(Collection> entries) {
    int distinct = entries.size();
    @SuppressWarnings("unchecked")
    Multisets.ImmutableEntry[] entryArray = new Multisets.ImmutableEntry[distinct];
    if (distinct == 0) {
      return new RegularImmutableMultiset<>(entryArray, null, 0, 0, ImmutableSet.of());
    }
    int tableSize = Hashing.closedTableSize(distinct, MAX_LOAD_FACTOR);
    int mask = tableSize - 1;
    @SuppressWarnings("unchecked")
    Multisets.ImmutableEntry[] hashTable = new Multisets.ImmutableEntry[tableSize];

    int index = 0;
    int hashCode = 0;
    long size = 0;
    for (Entry entry : entries) {
      E element = checkNotNull(entry.getElement());
      int count = entry.getCount();
      int hash = element.hashCode();
      int bucket = Hashing.smear(hash) & mask;
      Multisets.ImmutableEntry bucketHead = hashTable[bucket];
      Multisets.ImmutableEntry newEntry;
      if (bucketHead == null) {
        boolean canReuseEntry =
            entry instanceof Multisets.ImmutableEntry && !(entry instanceof NonTerminalEntry);
        newEntry =
            canReuseEntry
                ? (Multisets.ImmutableEntry) entry
                : new Multisets.ImmutableEntry(element, count);
      } else {
        newEntry = new NonTerminalEntry(element, count, bucketHead);
      }
      hashCode += hash ^ count;
      entryArray[index++] = newEntry;
      hashTable[bucket] = newEntry;
      size += count;
    }

    return hashFloodingDetected(hashTable)
        ? JdkBackedImmutableMultiset.create(ImmutableList.asImmutableList(entryArray))
        : new RegularImmutableMultiset(
            entryArray, hashTable, Ints.saturatedCast(size), hashCode, null);
  }

  private static boolean hashFloodingDetected(Multisets.ImmutableEntry[] hashTable) {
    for (int i = 0; i < hashTable.length; i++) {
      int bucketLength = 0;
      for (Multisets.ImmutableEntry entry = hashTable[i];
          entry != null;
          entry = entry.nextInBucket()) {
        bucketLength++;
        if (bucketLength > MAX_HASH_BUCKET_LENGTH) {
          return true;
        }
      }
    }
    return false;
  }

  /**
   * Closed addressing tends to perform well even with high load factors. Being conservative here
   * ensures that the table is still likely to be relatively sparse (hence it misses fast) while
   * saving space.
   */
  @VisibleForTesting static final double MAX_LOAD_FACTOR = 1.0;

  /**
   * Maximum allowed false positive probability of detecting a hash flooding attack given random
   * input.
   */
  @VisibleForTesting static final double HASH_FLOODING_FPP = 0.001;

  /**
   * Maximum allowed length of a hash table bucket before falling back to a j.u.HashMap based
   * implementation. Experimentally determined.
   */
  @VisibleForTesting static final int MAX_HASH_BUCKET_LENGTH = 9;

  private final transient Multisets.ImmutableEntry[] entries;
  @NullableDecl private final transient Multisets.ImmutableEntry[] hashTable;
  private final transient int size;
  private final transient int hashCode;

  @LazyInit private transient ImmutableSet elementSet;

  private RegularImmutableMultiset(
      ImmutableEntry[] entries,
      ImmutableEntry[] hashTable,
      int size,
      int hashCode,
      ImmutableSet elementSet) {
    this.entries = entries;
    this.hashTable = hashTable;
    this.size = size;
    this.hashCode = hashCode;
    this.elementSet = elementSet;
  }

  private static final class NonTerminalEntry extends Multisets.ImmutableEntry {
    private final Multisets.ImmutableEntry nextInBucket;

    NonTerminalEntry(E element, int count, ImmutableEntry nextInBucket) {
      super(element, count);
      this.nextInBucket = nextInBucket;
    }

    @Override
    public ImmutableEntry nextInBucket() {
      return nextInBucket;
    }
  }

  @Override
  boolean isPartialView() {
    return false;
  }

  @Override
  public int count(@NullableDecl Object element) {
    Multisets.ImmutableEntry[] hashTable = this.hashTable;
    if (element == null || hashTable == null) {
      return 0;
    }
    int hash = Hashing.smearedHash(element);
    int mask = hashTable.length - 1;
    for (Multisets.ImmutableEntry entry = hashTable[hash & mask];
        entry != null;
        entry = entry.nextInBucket()) {
      if (Objects.equal(element, entry.getElement())) {
        return entry.getCount();
      }
    }
    return 0;
  }

  @Override
  public int size() {
    return size;
  }

  @Override
  public ImmutableSet elementSet() {
    ImmutableSet result = elementSet;
    return (result == null) ? elementSet = new ElementSet(Arrays.asList(entries), this) : result;
  }

  @Override
  Entry getEntry(int index) {
    return entries[index];
  }

  @Override
  public int hashCode() {
    return hashCode;
  }
}
    
    
    
    

    




    
    
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