| /* |
| * 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. |
| */ |
| |
| /* $Id$ */ |
| |
| package org.apache.fop.util; |
| |
| /** |
| * A utility class that provides helper methods for implementing equals and hashCode. |
| */ |
| public final class CompareUtil { |
| |
| private static final Object TIE_LOCK = new Object(); |
| |
| private CompareUtil() { |
| } |
| |
| /** |
| * Compares two objects for equality. |
| * In order to prevent lock-ordering deadlocks the following strategy is used: |
| * when two non null objects are passed to the method, the comparison |
| * is done by calling the {@link Object#equals(Object)} method of the object |
| * with the lower hash code ({@link System#identityHashCode(Object)}); |
| * in the rare case that two different objects have the same hash code, a lock |
| * is used. |
| * |
| * @param o1 an object |
| * @param o2 another object |
| * @return true if either o1 and o2 are null or if o1.equals(o2) |
| */ |
| public static boolean equal(Object o1, Object o2) { |
| int o1Hash = System.identityHashCode(o1); |
| int o2Hash = System.identityHashCode(o2); |
| if (o1Hash == o2Hash && o1 != o2 && o1Hash != 0) { |
| // in the rare case of different objects with the same hash code, |
| // the tieLock object is used to synchronize access |
| synchronized (TIE_LOCK) { |
| return o1.equals(o2); |
| } |
| } |
| if (o1Hash > o2Hash) { |
| Object tmp = o1; |
| o1 = o2; |
| o2 = tmp; |
| } |
| return o1 == null ? o2 == null : o1 == o2 || o1.equals(o2); |
| } |
| |
| /** |
| * Returns the hash code of the given object. |
| * |
| * @param object an object |
| * @return object.hashCode(), or 0 if object is null |
| */ |
| public static int getHashCode(Object object) { |
| return object == null ? 0 : object.hashCode(); |
| } |
| |
| /** |
| * Compares two numbers for equality. Uses the same comparison algorithm as |
| * the {@link Double#equals(Object)} method. |
| * |
| * @param n1 a number |
| * @param n2 another number |
| * @return true if the two numbers are equal, false otherwise |
| */ |
| public static boolean equal(double n1, double n2) { |
| return Double.doubleToLongBits(n1) == Double.doubleToLongBits(n2); |
| } |
| |
| /** |
| * Returns a hash code for the given number. Applies the same algorithm as |
| * the {@link Double#hashCode()} method. |
| * |
| * @param number a number |
| * @return a hash code for that number |
| */ |
| public static int getHashCode(double number) { |
| long bits = Double.doubleToLongBits(number); |
| return (int) (bits ^ (bits >>> 32)); |
| } |
| |
| } |