    001/*
    002 * Licensed to the Apache Software Foundation (ASF) under one or more
    003 * contributor license agreements.  See the NOTICE file distributed with
    004 * this work for additional information regarding copyright ownership.
    005 * The ASF licenses this file to You under the Apache License, Version 2.0
    006 * (the "License"); you may not use this file except in compliance with
    007 * the License.  You may obtain a copy of the License at
    008 *
    009 *      http://www.apache.org/licenses/LICENSE-2.0
    010 *
    011 * Unless required by applicable law or agreed to in writing, software
    012 * distributed under the License is distributed on an "AS IS" BASIS,
    013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    014 * See the License for the specific language governing permissions and
    015 * limitations under the License.
    016 */
    017package org.apache.commons.collections4.functors;
    018
    019import java.io.Serializable;
    020
    021import org.apache.commons.collections4.Equator;
    022
    023/**
    024 * Default {@link Equator} implementation.
    025 *
    026 * @param <T>  the types of object this {@link Equator} can evaluate.
    027 * @since 4.0
    028 */
    029public class DefaultEquator<T> implements Equator<T>, Serializable {
    030
    031    /** Serial version UID */
    032    private static final long serialVersionUID = 825802648423525485L;
    033
    034    /** Static instance */
    035    @SuppressWarnings("rawtypes") // the static instance works for all types
    036    public static final DefaultEquator INSTANCE = new DefaultEquator<>();
    037
    038    /**
    039     * Hashcode used for <code>null</code> objects.
    040     */
    041    public static final int HASHCODE_NULL = -1;
    042
    043    /**
    044     * Factory returning the typed singleton instance.
    045     *
    046     * @param <T>  the object type
    047     * @return the singleton instance
    048     */
    049    @SuppressWarnings("unchecked") // the static instance works for all types
    050    public static <T> DefaultEquator<T> defaultEquator() {
    051        return DefaultEquator.INSTANCE;
    052    }
    053
    054    /**
    055     * Restricted constructor.
    056     */
    057    private DefaultEquator() {
    058        super();
    059    }
    060
    061    /**
    062     * {@inheritDoc} Delegates to {@link Object#equals(Object)}.
    063     */
    064    @Override
    065    public boolean equate(final T o1, final T o2) {
    066        return o1 == o2 || o1 != null && o1.equals(o2);
    067    }
    068
    069    /**
    070     * {@inheritDoc}
    071     *
    072     * @return <code>o.hashCode()</code> if <code>o</code> is non-
    073     *         <code>null</code>, else {@link #HASHCODE_NULL}.
    074     */
    075    @Override
    076    public int hash(final T o) {
    077        return o == null ? HASHCODE_NULL : o.hashCode();
    078    }
    079
    080    private Object readResolve() {
    081        return INSTANCE;
    082    }
    083
    084}