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Apache Commons Lang, a package of Java utility classes for the classes that are in java.lang's hierarchy, or are considered to be so standard as to justify existence in java.lang.

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/*
 * 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.lang3.reflect;

import org.apache.commons.lang3.BooleanUtils;

/**
 * Utility methods focusing on inheritance.
 *
 * @since 3.2
 */
public class InheritanceUtils {

    /**
     * {@link InheritanceUtils} instances should NOT be constructed in standard programming.
     * Instead, the class should be used as
     * {@code MethodUtils.getAccessibleMethod(method)}.
     *
     * This constructor is {@code public} to permit tools that require a JavaBean
     * instance to operate.
     */
    public InheritanceUtils() {
        super();
    }

    /**
     * Returns the number of inheritance hops between two classes.
     *
     * @param child the child class, may be {@code null}
     * @param parent the parent class, may be {@code null}
     * @return the number of generations between the child and parent; 0 if the same class;
     * -1 if the classes are not related as child and parent (includes where either class is null)
     * @since 3.2
     */
    public static int distance(final Class child, final Class parent) {
        if (child == null || parent == null) {
            return -1;
        }

        if (child.equals(parent)) {
            return 0;
        }

        final Class cParent = child.getSuperclass();
        int d = BooleanUtils.toInteger(parent.equals(cParent));

        if (d == 1) {
            return d;
        } else {
            d += distance(cParent, parent);
            return d > 0 ? d + 1 : -1;
        }
    }
}