/*

 * 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;

/**

 * An equation function, which determines equality between objects of type T.

 * <p>

 * It is the functional sibling of {@link java.util.Comparator}; {@link Equator} is to

 * {@link Object} as {@link java.util.Comparator} is to {@link java.lang.Comparable}.

 * </p>

 *

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

 * @since 4.0

 */

public interface Equator<T> {

    /**

     * Evaluates the two arguments for their equality.

     *

     * @param o1 the first object to be equated.

     * @param o2 the second object to be equated.

     * @return whether the two objects are equal.

     */

    boolean equate(T o1, T o2);

    /**

     * Calculates the hash for the object, based on the method of equality used in the equate

     * method. This is used for classes that delegate their {@link Object#equals(Object) equals(Object)} method to an

     * Equator (and so must also delegate their {@link Object#hashCode() hashCode()} method), or for implementations

     * of {@link org.apache.commons.collections4.map.HashedMap} that use an Equator for the key objects.

     *

     * @param o the object to calculate the hash for.

     * @return the hash of the object.

     */

    int hash(T o);

}