HashCodeUtil.java

/*
@VaadinAddonLicenseForJavaFiles@
 */
package com.spaceapplications.vaadin.addon.eventtimeline.gwt.client;

/**
 * Collected methods which allow easy implementation of <code>hashCode</code>.
 * 
 * Example use case:
 * 
 * <pre>
 * public int hashCode() {
 *   int result = HashCodeUtil.SEED;
 *   // collect the contributions of various fields
 *   result = HashCodeUtil.hash(result, fPrimitive);
 *   result = HashCodeUtil.hash(result, fObject);
 *   return result;
 * }
 * </pre>
 */
public final class HashCodeUtil {

  /**
   * An initial value for a <code>hashCode</code>, to which is added
   * contributions from fields. Using a non-zero value decreases collisons of
   * <code>hashCode</code> values.
   */
  public static final int SEED = 23;

  /**
   * booleans.
   */
  public static int hash(int aSeed, boolean aBoolean) {
    return firstTerm(aSeed) + (aBoolean ? 1 : 0);
  }

  /**
   * chars.
   */
  public static int hash(int aSeed, char aChar) {
    return firstTerm(aSeed) + (int) aChar;
  }

  /**
   * ints.
   */
  public static int hash(int aSeed, int aInt) {
    /*
     * Implementation Note: byte and short are handled by this method, through
     * implicit conversion.
     */
    return firstTerm(aSeed) + aInt;
  }

  /**
   * longs.
   */
  public static int hash(int aSeed, long aLong) {
    return firstTerm(aSeed) + (int) (aLong ^ (aLong >>> 32));
  }

  /**
   * <code>aObject</code> is a possibly-null object field, and possibly an
   * array.
   * 
   * If <code>aObject</code> is an array, then each element may be a primitive
   * or a possibly-null object.
   */
  public static int hash(int aSeed, Object aObject) {
    int result = aSeed;
    if (aObject == null) {
      result = hash(result, 0);
    } else if (!isArray(aObject)) {
      result = hash(result, aObject.hashCode());
    } 
    return result;
  }

  // / PRIVATE ///
  private static final int fODD_PRIME_NUMBER = 37;

  private static int firstTerm(int aSeed) {
    return fODD_PRIME_NUMBER * aSeed;
  }

  private static boolean isArray(Object aObject) {
    return aObject.getClass().isArray();
  }
}