A hash-code generator and a collection of static hash-code generation methods. : Hash Code « Development Class « Java






A hash-code generator and a collection of static hash-code generation methods.

         
 
/*
 * JBoss, Home of Professional Open Source
 * Copyright 2005, JBoss Inc., and individual contributors as indicated
 * by the @authors tag. See the copyright.txt in the distribution for a
 * full listing of individual contributors.
 *
 * This is free software; you can redistribute it and/or modify it
 * under the terms of the GNU Lesser General Public License as
 * published by the Free Software Foundation; either version 2.1 of
 * the License, or (at your option) any later version.
 *
 * This software is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this software; if not, write to the Free
 * Software Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA
 * 02110-1301 USA, or see the FSF site: http://www.fsf.org.
 */

import java.io.Serializable;

/**
 * A hash-code generator and a collection of static hash-code generation
 * methods.
 * 
 * @version <tt>$Revision: 2800 $</tt>
 * @author <a href="mailto:jason@planet57.com">Jason Dillon</a>
 */
@SuppressWarnings("unchecked")
public final class HashCode implements Serializable, Cloneable, Comparable {
  /** The serialVersionUID */
  private static final long serialVersionUID = 2391396931740264021L;

  /** Hashcode for a 'null' value. */
  private static final int NULL_HASHCODE = 0;

  /** Hashcode for a 'true' boolean */
  private static final int TRUE_HASHCODE = 1231; // completely arbitrary

  /** Hashcode for a 'false' boolean */
  private static final int FALSE_HASHCODE = 1237; // completely arbitrary

  /** The hash-code value. */
  private int value;

  /**
   * Construct a new <tt>HashCode</tt> using the given <tt>int</tt> as the
   * base value.
   * 
   * @param value
   *          <tt>int</tt> to use as the base value.
   */
  public HashCode(final int value) {
    this.value = value;
  }

  /**
   * Construct a new <tt>HashCode</tt>.
   */
  public HashCode() {
    this(0);
  }

  /**
   * Add the hash-code of the given value.
   * 
   * @param b
   *          Value to get hash-code from.
   * @return <i>This</i> <tt>HashCode</tt>.
   */
  public HashCode add(final boolean b) {
    value ^= generate(b);
    return this;
  }

  /**
   * Add the hash-code of the given value.
   * 
   * @param n
   *          Value to get hash-code from.
   * @return <i>This</i> <tt>HashCode</tt>.
   */
  public HashCode add(final byte n) {
    value ^= n;
    return this;
  }

  /**
   * Add the hash-code of the given value.
   * 
   * @param n
   *          Value to get hash-code from.
   * @return <i>This</i> <tt>HashCode</tt>.
   */
  public HashCode add(final char n) {
    value ^= n;
    return this;
  }

  /**
   * Add the hash-code of the given value.
   * 
   * @param n
   *          Value to get hash-code from.
   * @return <i>This</i> <tt>HashCode</tt>.
   */
  public HashCode add(final short n) {
    value ^= n;
    return this;
  }

  /**
   * Add the hash-code of the given value.
   * 
   * @param n
   *          Value to get hash-code from.
   * @return <i>This</i> <tt>HashCode</tt>.
   */
  public HashCode add(final int n) {
    value ^= n;
    return this;
  }

  /**
   * Add the hash-code of the given value.
   * 
   * @param n
   *          Value to get hash-code from.
   * @return <i>This</i> <tt>HashCode</tt>.
   */
  public HashCode add(final long n) {
    value ^= generate(n);
    return this;
  }

  /**
   * Add the hash-code of the given value.
   * 
   * @param f
   *          Value to get hash-code from.
   * @return <i>This</i> <tt>HashCode</tt>.
   */
  public HashCode add(final float f) {
    value ^= generate(f);
    return this;
  }

  /**
   * Add the hash-code of the given value.
   * 
   * @param f
   *          Value to get hash-code from.
   * @return <i>This</i> <tt>HashCode</tt>.
   */
  public HashCode add(final double f) {
    value ^= generate(f);
    return this;
  }

  /**
   * Add the hash-code of the given object.
   * 
   * @param obj
   *          Value to get hash-code from.
   * @return <i>This</i> <tt>HashCode</tt>.
   */
  public HashCode add(final Object obj) {
    value ^= generate(obj);
    return this;
  }

  /**
   * Get the hash-code.
   * 
   * @return Hash-code.
   */
  public int hashCode() {
    return value;
  }

  /**
   * Compares this object with the specified <tt>int</tt> for order.
   * 
   * @param other
   *          Value to compare with.
   * @return A negative integer, zero, or a positive integer as this object is
   *         less than, equal to, or greater than the specified object.
   */
  public int compareTo(final int other) {
    return (value < other) ? -1 : (value == other) ? 0 : 1;
  }

  /**
   * Compares this object with the specified object for order.
   * 
   * @param obj
   *          Value to compare with.
   * @return A negative integer, zero, or a positive integer as this object is
   *         less than, equal to, or greater than the specified object.
   * 
   * @throws ClassCastException
   *           Object is not a <tt>HashCode</tt>.
   */
  public int compareTo(final Object obj) throws ClassCastException {
    HashCode hashCode = (HashCode) obj;
    return compareTo(hashCode.value);
  }

  /**
   * Test the equality of this <tt>HashCode</tt> and another object.
   * 
   * @param obj
   *          Object to test equality with.
   * @return True if object is equal.
   */
  public boolean equals(final Object obj) {
    if (obj == this)
      return true;

    if (obj != null && obj.getClass() == getClass()) {
      return value == ((HashCode) obj).value;
    }

    return false;
  }

  /**
   * Return a string representation of this <tt>HashCode</tt>.
   * 
   * @return A string representation of this <tt>HashCode</tt>.
   */
  public String toString() {
    return String.valueOf(value);
  }

  /**
   * Return a cloned copy of this <tt>HashCode</tt>.
   * 
   * @return Cloned <tt>HashCode</tt>.
   */
  public Object clone() {
    try {
      return super.clone();
    } catch (CloneNotSupportedException e) {
      throw new InternalError();
    }
  }

  // ///////////////////////////////////////////////////////////////////////
  // Generation Methods //
  // ///////////////////////////////////////////////////////////////////////

  /**
   * Generate a hash code for a boolean value.
   * 
   * @param value
   *          Boolean value to generate hash code from.
   * @return Hash code.
   */
  public static int generate(final boolean value) {
    return value ? TRUE_HASHCODE : FALSE_HASHCODE;
  }

  /**
   * Generate a hash code for a long value.
   * 
   * @param value
   *          Long value to generate hash code from.
   * @return Hash code.
   */
  public static int generate(final long value) {
    return (int) (value ^ (value >> 32));
  }

  /**
   * Generate a hash code for a double value.
   * 
   * @param value
   *          Double value to generate hash code from.
   * @return Hash code.
   */
  public static int generate(final double value) {
    return generate(Double.doubleToLongBits(value));
  }

  /**
   * Generate a hash code for a float value.
   * 
   * @param value
   *          Float value to generate hash code from.
   * @return Hash code.
   */
  public static int generate(final float value) {
    return Float.floatToIntBits(value);
  }

  /**
   * Generate a hash code for a byte array.
   * 
   * @param bytes
   *          An array of bytes to generate a hash code from.
   * @return Hash code.
   */
  public static int generate(final byte[] bytes) {
    int hashcode = 0;

    for (int i = 0; i < bytes.length; i++) {
      hashcode <<= 1;
      hashcode ^= bytes[i];
    }

    return hashcode;
  }

  /**
   * Generate a hash code for an object array.
   * 
   * <p>
   * Does not handle nested primitive array elements.
   * 
   * @param array
   *          Array to generate hashcode for.
   * @param deep
   *          True to traverse elements which are arrays to determine the
   *          elements hash code.
   * @return Hash code.
   */
  public static int generate(final Object array[], final boolean deep) {
    int hashcode = 0;

    for (int i = 0; i < array.length; i++) {
      if (deep && (array[i] instanceof Object[])) {
        hashcode ^= generate((Object[]) array[i], true);
      } else {
        hashcode ^= array[i].hashCode();
      }
    }

    return hashcode;
  }

  /**
   * Generate a shallow hash code for an object array.
   * 
   * @param array
   *          Array to generate hashcode for.
   * @return Hash code.
   */
  public static int generate(final Object array[]) {
    return generate(array, false);
  }

  /**
   * Generate a hash code for an object.
   * 
   * @param obj
   *          Object to generate hashcode for.
   * @return Hash code.
   */
  public static int generate(final Object obj) {
    if (obj != null) {
      return obj.hashCode();
    }

    return NULL_HASHCODE;
  }
}

   
    
    
    
    
    
    
    
    
  








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