    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.lang3.builder;
    018
    019/**
    020 * <p>{@code Diffable} classes can be compared with other objects
    021 * for differences. The {@link DiffResult} object retrieved can be queried
    022 * for a list of differences or printed using the {@link DiffResult#toString()}.</p>
    023 *
    024 * <p>The calculation of the differences is <i>consistent with equals</i> if
    025 * and only if {@code d1.equals(d2)} implies {@code d1.diff(d2) == ""}.
    026 * It is strongly recommended that implementations are consistent with equals
    027 * to avoid confusion. Note that {@code null} is not an instance of any class
    028 * and {@code d1.diff(null)} should throw a {@code NullPointerException}.</p>
    029 *
    030 * <p>
    031 * {@code Diffable} classes lend themselves well to unit testing, in which a
    032 * easily readable description of the differences between an anticipated result and
    033 * an actual result can be retrieved. For example:
    034 * </p>
    035 * <pre>
    036 * Assert.assertEquals(expected.diff(result), expected, result);
    037 * </pre>
    038 *
    039 * @param <T> the type of objects that this object may be differentiated against
    040 * @since 3.3
    041 */
    042public interface Diffable<T> {
    043
    044    /**
    045     * <p>Retrieves a list of the differences between
    046     * this object and the supplied object.</p>
    047     *
    048     * @param obj the object to diff against, can be {@code null}
    049     * @return a list of differences
    050     * @throws NullPointerException if the specified object is {@code null}
    051     */
    052    DiffResult diff(T obj);
    053}