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Provides a simple model for integrating Ehcache in a Spring project via annotations.

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/**
 * Copyright 2010 Nicholas Blair, Eric Dalquist
 *
 * 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.googlecode.ecache.annotations.key;

/**
 * 
 * Builds the checksum and hash code needed to create a
 * {@link HashCodeCacheKey}.
 * 
 *
 * @author Omar Irbouh
 * @author Alex Ruiz
 */
public final class HashCodeCalculator {

  private static final int INITIAL_HASH = 17;

  private static final int MULTIPLIER = 37;

  private long checkSum;

  /**
   * Counts the number of times {@link #append(int)} is executed.
   * It is also used to build {@link #checkSum} and
   * {@link #hashCode}.
   */
  private int count;

  /**
   * Hash code to build;
   */
  private int hashCode;

  /**
   * Constructor.
   */
  public HashCodeCalculator() {
    super();
    hashCode = INITIAL_HASH;
  }

  /**
   * Recalculates {@link #checkSum} and
   * {@link #hashCode} using the specified value.
   *
   * @param value
   *          the specified value.
   */
  public void append(int value) {
    count++;
    int valueToAppend = count * value;

    hashCode = MULTIPLIER * hashCode + (valueToAppend ^ (valueToAppend >>> 16));
    checkSum += valueToAppend;
  }

  /**
   * @return the number that ensures that the combination hashCode/checSum is
   *         unique
   */
  public long getCheckSum() {
    return checkSum;
  }

  /**
   * @return the calculated hash code
   */
  public int getHashCode() {
    return hashCode;
  }
}