    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;
    020import java.util.Objects;
    021
    022import org.apache.commons.collections4.Equator;
    023
    024/**
    025 * Default {@link Equator} implementation.
    026 *
    027 * @param <T>  the types of object this {@link Equator} can evaluate.
    028 * @since 4.0
    029 */
    030public class DefaultEquator<T> implements Equator<T>, Serializable {
    031
    032    /** Serial version UID */
    033    private static final long serialVersionUID = 825802648423525485L;
    034
    035    /** Static instance */
    036    @SuppressWarnings("rawtypes") // the static instance works for all types
    037    public static final DefaultEquator INSTANCE = new DefaultEquator<>();
    038
    039    /**
    040     * Hashcode used for {@code null} objects.
    041     */
    042    public static final int HASHCODE_NULL = -1;
    043
    044    /**
    045     * Factory returning the typed singleton instance.
    046     *
    047     * @param <T>  the object type
    048     * @return the singleton instance
    049     */
    050    public static <T> DefaultEquator<T> defaultEquator() {
    051        return INSTANCE;
    052    }
    053
    054    /**
    055     * Restricted constructor.
    056     */
    057    private DefaultEquator() {
    058    }
    059
    060    /**
    061     * {@inheritDoc} Delegates to {@link Objects#equals(Object, Object)}.
    062     */
    063    @Override
    064    public boolean equate(final T o1, final T o2) {
    065        return Objects.equals(o1, o2);
    066    }
    067
    068    /**
    069     * {@inheritDoc}
    070     *
    071     * @return {@code o.hashCode()} if {@code o} is non-
    072     *         {@code null}, else {@link #HASHCODE_NULL}.
    073     */
    074    @Override
    075    public int hash(final T o) {
    076        return o == null ? HASHCODE_NULL : o.hashCode();
    077    }
    078
    079    /**
    080     * Returns the singleton instance.
    081     *
    082     * @return the singleton instance.
    083     */
    084    private Object readResolve() {
    085        return INSTANCE;
    086    }
    087
    088}