content: /*
   * Licensed to the Apache Software Foundation (ASF) under one or more
   * contributor license agreements.  See the NOTICE file distributed with
   * this work for additional information regarding copyright ownership.
   * The ASF licenses this file to You 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 org.apache.commons.lang.builder;
  
  import java.util.HashSet;
  import java.util.Set;
  
  /**
   * <p>
   * Assists in implementing {@link Object#hashCode()} methods.
   * </p>
   * <p/>
   * <p>
   * This class enables a good <code>hashCode</code> method to be built for any class. It follows the rules laid out in
   * the book <a href="http://java.sun.com/docs/books/effective/index.html">Effective Java</a> by Joshua Bloch. Writing a
   * good <code>hashCode</code> method is actually quite difficult. This class aims to simplify the process.
   * </p>
   * <p/>
   * <p>
   * All relevant fields from the object should be included in the <code>hashCode</code> method. Derived fields may be
   * excluded. In general, any field used in the <code>equals</code> method must be used in the <code>hashCode</code>
   * method.
   * </p>
   * <p/>
   * <p>
   * To use this class write code as follows:
   * </p>
   * <p/>
   * <pre>
   * public class Person {
   *   String name;
   *   int age;
   *   boolean smoker;
   *   ...
   *
   *   public int hashCode() {
   *     // you pick a hard-coded, randomly chosen, non-zero, odd number
   *     // ideally different for each class
   *     return new HashCodeBuilder(17, 37).
   *       append(name).
   *       append(age).
   *       append(smoker).
   *       toHashCode();
   *   }
   * }
   * </pre>
   * <p/>
   * <p>
   * If required, the superclass <code>hashCode()</code> can be added using {@link #appendSuper}.
   * </p>
   * <p/>
   * <p>
   * Alternatively, there is a method that uses reflection to determine the fields to test. Because these fields are
   * usually private, the method, <code>reflectionHashCode</code>, uses <code>AccessibleObject.setAccessible</code>
   * to change the visibility of the fields. This will fail under a security manager, unless the appropriate permissions
   * are set up correctly. It is also slower than testing explicitly.
   * </p>
   * <p/>
   * <p>
   * A typical invocation for this method would look like:
   * </p>
   * <p/>
   * <pre>
   * public int hashCode() {
   *   return HashCodeBuilder.reflectionHashCode(this);
   * }
   * </pre>
   *
   * @author Stephen Colebourne
   * @author Gary Gregory
   * @author Pete Gieser
   * @version $Id: HashCodeBuilder.java 447989 2006-09-19 21:58:11Z ggregory $
   * @since 1.0
   */
  public class HashCodeBuilder {
      /**
       * <p>
       * A registry of objects used by reflection methods to detect cyclical object references and avoid infinite loops.
       * </p>
       *
       * @since 2.3
       */
      private static final ThreadLocal registry = new ThreadLocal() {
          protected synchronized Object initialValue() {
              // The HashSet implementation is not synchronized,
              // which is just what we need here.
              return new HashSet();
          }
      };
  
      /**
       * <p>
       * Returns the registry of objects being traversed by the reflection methods in the current thread.
       * </p>
       *
       * @return Set the registry of objects being traversed
       * @since 2.3
       */
      static Set getRegistry() {
          return (Set) registry.get();
      }
  
      /**
       * <p>
       * Returns <code>true</code> if the registry contains the given object. Used by the reflection methods to avoid
       * infinite loops.
       * </p>
       *
       * @param value The object to lookup in the registry.
       * @return boolean <code>true</code> if the registry contains the given object.
       * @since 2.3
       */
      static boolean isRegistered(Object value) {
          return getRegistry().contains(toIdentityHashCodeInteger(value));
      }
  
      // -------------------------------------------------------------------------
  
      /**
       * <p>
       * Registers the given object. Used by the reflection methods to avoid infinite loops.
       * </p>
       *
       * @param value The object to register.
       */
      static void register(Object value) {
          getRegistry().add(toIdentityHashCodeInteger(value));
      }
  
      /**
       * Returns an Integer for the given object's default hash code.
       *
       * @param value object for which the hashCode is to be calculated
       * @return Default int hash code
       * @see System#identityHashCode(Object)
       */
      private static Integer toIdentityHashCodeInteger(Object value) {
          return System.identityHashCode(value);
      }
  
      /**
       * <p>
       * Unregisters the given object.
       * </p>
       * <p/>
       * <p/>
       * Used by the reflection methods to avoid infinite loops.
       *
       * @param value The object to unregister.
       * @since 2.3
       */
      static void unregister(Object value) {
          getRegistry().remove(toIdentityHashCodeInteger(value));
      }
  
      /**
       * Constant to use in building the hashCode.
       */
      private final int iConstant;
  
      /**
       * Running total of the hashCode.
       */
      private int iTotal = 0;
  
      /**
       * <p>
       * Uses two hard coded choices for the constants needed to build a <code>hashCode</code>.
       * </p>
       */
      public HashCodeBuilder() {
          iConstant = 37;
          iTotal = 17;
      }
  
      /**
       * <p>
       * Two randomly chosen, non-zero, odd numbers must be passed in. Ideally these should be different for each class,
       * however this is not vital.
       * </p>
       * <p/>
       * <p>
       * Prime numbers are preferred, especially for the multiplier.
       * </p>
       *
       * @param initialNonZeroOddNumber    a non-zero, odd number used as the initial value
       * @param multiplierNonZeroOddNumber a non-zero, odd number used as the multiplier
       * @throws IllegalArgumentException if the number is zero or even
       */
      public HashCodeBuilder(int initialNonZeroOddNumber, int multiplierNonZeroOddNumber) {
          if (initialNonZeroOddNumber == 0) {
              throw new IllegalArgumentException("HashCodeBuilder requires a non zero initial value");
          }
          if (initialNonZeroOddNumber % 2 == 0) {
              throw new IllegalArgumentException("HashCodeBuilder requires an odd initial value");
          }
          if (multiplierNonZeroOddNumber == 0) {
              throw new IllegalArgumentException("HashCodeBuilder requires a non zero multiplier");
          }
          if (multiplierNonZeroOddNumber % 2 == 0) {
              throw new IllegalArgumentException("HashCodeBuilder requires an odd multiplier");
          }
          iConstant = multiplierNonZeroOddNumber;
          iTotal = initialNonZeroOddNumber;
      }
  
      /**
       * <p>
       * Append a <code>hashCode</code> for a <code>boolean</code>.
       * </p>
       * <p>
       * This adds <code>iConstant * 1</code> to the <code>hashCode</code> and not a <code>1231</code> or
       * <code>1237</code> as done in java.lang.Boolean. This is in accordance with the <quote>Effective Java</quote>
       * design.
       * </p>
       *
       * @param value the boolean to add to the <code>hashCode</code>
       * @return this
       */
      public HashCodeBuilder append(boolean value) {
          iTotal = iTotal * iConstant + (value ? 0 : 1);
          return this;
      }
  
      /**
       * <p>
       * Append a <code>hashCode</code> for a <code>boolean</code> array.
       * </p>
       *
       * @param array the array to add to the <code>hashCode</code>
       * @return this
       */
      public HashCodeBuilder append(boolean[] array) {
          if (array == null) {
              iTotal = iTotal * iConstant;
          } else {
              for (boolean anArray : array) {
                  append(anArray);
              }
          }
          return this;
      }
  
      // -------------------------------------------------------------------------
  
      /**
       * <p>
       * Append a <code>hashCode</code> for a <code>byte</code>.
       * </p>
       *
       * @param value the byte to add to the <code>hashCode</code>
       * @return this
       */
      public HashCodeBuilder append(byte value) {
          iTotal = iTotal * iConstant + value;
          return this;
      }
  
      // -------------------------------------------------------------------------
  
      /**
       * <p>
       * Append a <code>hashCode</code> for a <code>byte</code> array.
       * </p>
       *
       * @param array the array to add to the <code>hashCode</code>
       * @return this
       */
      public HashCodeBuilder append(byte[] array) {
          if (array == null) {
              iTotal = iTotal * iConstant;
          } else {
              for (byte anArray : array) {
                  append(anArray);
              }
          }
          return this;
      }
  
      /**
       * <p>
       * Append a <code>hashCode</code> for a <code>char</code>.
       * </p>
       *
       * @param value the char to add to the <code>hashCode</code>
       * @return this
       */
      public HashCodeBuilder append(char value) {
          iTotal = iTotal * iConstant + value;
          return this;
      }
  
      /**
       * <p>
       * Append a <code>hashCode</code> for a <code>char</code> array.
       * </p>
       *
       * @param array the array to add to the <code>hashCode</code>
       * @return this
       */
      public HashCodeBuilder append(char[] array) {
          if (array == null) {
              iTotal = iTotal * iConstant;
          } else {
              for (char anArray : array) {
                  append(anArray);
              }
          }
          return this;
      }
  
      /**
       * <p>
       * Append a <code>hashCode</code> for a <code>double</code>.
       * </p>
       *
       * @param value the double to add to the <code>hashCode</code>
       * @return this
       */
      public HashCodeBuilder append(double value) {
          return append(Double.doubleToLongBits(value));
      }
  
      /**
       * <p>
       * Append a <code>hashCode</code> for a <code>double</code> array.
       * </p>
       *
       * @param array the array to add to the <code>hashCode</code>
       * @return this
       */
      public HashCodeBuilder append(double[] array) {
          if (array == null) {
              iTotal = iTotal * iConstant;
          } else {
              for (double anArray : array) {
                  append(anArray);
              }
          }
          return this;
      }
  
      /**
       * <p>
       * Append a <code>hashCode</code> for a <code>float</code>.
       * </p>
       *
       * @param value the float to add to the <code>hashCode</code>
       * @return this
       */
      public HashCodeBuilder append(float value) {
          iTotal = iTotal * iConstant + Float.floatToIntBits(value);
          return this;
      }
  
      /**
       * <p>
       * Append a <code>hashCode</code> for a <code>float</code> array.
       * </p>
       *
       * @param array the array to add to the <code>hashCode</code>
       * @return this
       */
      public HashCodeBuilder append(float[] array) {
          if (array == null) {
              iTotal = iTotal * iConstant;
          } else {
              for (float anArray : array) {
                  append(anArray);
              }
          }
          return this;
      }
  
      /**
       * <p>
       * Append a <code>hashCode</code> for an <code>int</code>.
       * </p>
       *
       * @param value the int to add to the <code>hashCode</code>
       * @return this
       */
      public HashCodeBuilder append(int value) {
          iTotal = iTotal * iConstant + value;
          return this;
      }
  
      /**
       * <p>
       * Append a <code>hashCode</code> for an <code>int</code> array.
       * </p>
       *
       * @param array the array to add to the <code>hashCode</code>
       * @return this
       */
      public HashCodeBuilder append(int[] array) {
          if (array == null) {
              iTotal = iTotal * iConstant;
          } else {
              for (int anArray : array) {
                  append(anArray);
              }
          }
          return this;
      }
  
      /**
       * <p>
       * Append a <code>hashCode</code> for a <code>long</code>.
       * </p>
       *
       * @param value the long to add to the <code>hashCode</code>
       * @return this
       */
      public HashCodeBuilder append(long value) {
          iTotal = iTotal * iConstant + ((int) (value ^ (value >> 32)));
          return this;
      }
  
      /**
       * <p>
       * Append a <code>hashCode</code> for a <code>long</code> array.
       * </p>
       *
       * @param array the array to add to the <code>hashCode</code>
       * @return this
       */
      public HashCodeBuilder append(long[] array) {
          if (array == null) {
              iTotal = iTotal * iConstant;
          } else {
              for (long anArray : array) {
                  append(anArray);
              }
          }
          return this;
      }
  
      /**
       * <p>
       * Append a <code>hashCode</code> for an <code>Object</code>.
       * </p>
       *
       * @param object the Object to add to the <code>hashCode</code>
       * @return this
       */
      public HashCodeBuilder append(Object object) {
          if (object == null) {
              iTotal = iTotal * iConstant;
  
          } else {
              if (object.getClass().isArray() == false) {
                  // the simple case, not an array, just the element
                  iTotal = iTotal * iConstant + object.hashCode();
  
              } else {
                  // 'Switch' on type of array, to dispatch to the correct handler
                  // This handles multi dimensional arrays
                  if (object instanceof long[]) {
                      append((long[]) object);
                  } else if (object instanceof int[]) {
                      append((int[]) object);
                  } else if (object instanceof short[]) {
                      append((short[]) object);
                  } else if (object instanceof char[]) {
                      append((char[]) object);
                  } else if (object instanceof byte[]) {
                      append((byte[]) object);
                  } else if (object instanceof double[]) {
                      append((double[]) object);
                  } else if (object instanceof float[]) {
                      append((float[]) object);
                  } else if (object instanceof boolean[]) {
                      append((boolean[]) object);
                  } else {
                      // Not an array of primitives
                      append((Object[]) object);
                  }
              }
          }
          return this;
      }
  
      /**
       * <p>
       * Append a <code>hashCode</code> for an <code>Object</code> array.
       * </p>
       *
       * @param array the array to add to the <code>hashCode</code>
       * @return this
       */
      public HashCodeBuilder append(Object[] array) {
          if (array == null) {
              iTotal = iTotal * iConstant;
          } else {
              for (Object anArray : array) {
                  append(anArray);
              }
          }
          return this;
      }
  
      /**
       * <p>
       * Append a <code>hashCode</code> for a <code>short</code>.
       * </p>
       *
       * @param value the short to add to the <code>hashCode</code>
       * @return this
       */
      public HashCodeBuilder append(short value) {
          iTotal = iTotal * iConstant + value;
          return this;
      }
  
      /**
       * <p>
       * Append a <code>hashCode</code> for a <code>short</code> array.
       * </p>
       *
       * @param array the array to add to the <code>hashCode</code>
       * @return this
       */
      public HashCodeBuilder append(short[] array) {
          if (array == null) {
              iTotal = iTotal * iConstant;
          } else {
              for (short anArray : array) {
                  append(anArray);
              }
          }
          return this;
      }
  
      /**
       * <p>
       * Adds the result of super.hashCode() to this builder.
       * </p>
       *
       * @param superHashCode the result of calling <code>super.hashCode()</code>
       * @return this HashCodeBuilder, used to chain calls.
       * @since 2.0
       */
      public HashCodeBuilder appendSuper(int superHashCode) {
          iTotal = iTotal * iConstant + superHashCode;
          return this;
      }
  
      /**
       * <p>
       * Return the computed <code>hashCode</code>.
       * </p>
       *
       * @return <code>hashCode</code> based on the fields appended
       */
      public int toHashCode() {
          return iTotal;
      }
  
  }