/*

 * 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.collections4.functors;

import java.io.Serializable;

import org.apache.commons.collections4.Equator;

/**

 * Default {@link Equator} implementation.

 *

 * @param <T>  the types of object this {@link Equator} can evaluate.

 * @since 4.0

 */

public class DefaultEquator<T> implements Equator<T>, Serializable {

    /** Serial version UID */

    private static final long serialVersionUID = 825802648423525485L;

    /** Static instance */

    @SuppressWarnings("rawtypes") // the static instance works for all types

    public static final DefaultEquator INSTANCE = new DefaultEquator<>();

    /**

     * Hashcode used for <code>null</code> objects.

     */

    public static final int HASHCODE_NULL = -1;

    /**

     * Factory returning the typed singleton instance.

     *

     * @param <T>  the object type

     * @return the singleton instance

     */

    public static <T> DefaultEquator<T> defaultEquator() {

        return DefaultEquator.INSTANCE;

    }

    /**

     * Restricted constructor.

     */

    private DefaultEquator() {

        super();

    }

    /**

     * {@inheritDoc} Delegates to {@link Object#equals(Object)}.

     */

    @Override

    public boolean equate(final T o1, final T o2) {

        return o1 == o2 || o1 != null && o1.equals(o2);

    }

    /**

     * {@inheritDoc}

     *

     * @return <code>o.hashCode()</code> if <code>o</code> is non-

     *         <code>null</code>, else {@link #HASHCODE_NULL}.

     */

    @Override

    public int hash(final T o) {

        return o == null ? HASHCODE_NULL : o.hashCode();

    }

    private Object readResolve() {

        return INSTANCE;

    }

}