log4j-core/src/main/java/org/apache/logging/log4j/core/util/ArrayUtils.java

/*
 * 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.logging.log4j.core.util;

import java.lang.reflect.Array;

/**
 * Copied from Apache Commons Lang (including the {@code @since} tags.)
 */
public class ArrayUtils {

    /**
     * <p>Returns the length of the specified array.
     * This method can deal with {@code Object} arrays and with primitive arrays.</p>
     *
     * <p>If the input array is {@code null}, {@code 0} is returned.</p>
     *
     * <pre>
     * ArrayUtils.getLength(null)            = 0
     * ArrayUtils.getLength([])              = 0
     * ArrayUtils.getLength([null])          = 1
     * ArrayUtils.getLength([true, false])   = 2
     * ArrayUtils.getLength([1, 2, 3])       = 3
     * ArrayUtils.getLength(["a", "b", "c"]) = 3
     * </pre>
     *
     * @param array  the array to retrieve the length from, may be null
     * @return The length of the array, or {@code 0} if the array is {@code null}
     * @throws IllegalArgumentException if the object argument is not an array.
     * @since 2.1
     */
    public static int getLength(final Object array) {
        if (array == null) {
            return 0;
        }
        return Array.getLength(array);
    }

    /**
     * Checks if an array of Objects is empty or {@code null}.
     *
     * @param array  the array to test
     * @return {@code true} if the array is empty or {@code null}
     * @since 2.1
     */
    public static boolean isEmpty(final byte[] array) {
        return getLength(array) == 0;
    }    

    /**
     * <p>Removes the element at the specified position from the specified array.
     * All subsequent elements are shifted to the left (subtracts one from
     * their indices).</p>
     *
     * <p>This method returns a new array with the same elements of the input
     * array except the element on the specified position. The component
     * type of the returned array is always the same as that of the input
     * array.</p>
     *
     * <p>If the input array is {@code null}, an IndexOutOfBoundsException
     * will be thrown, because in that case no valid index can be specified.</p>
     *
     * @param array  the array to remove the element from, may not be {@code null}
     * @param index  the position of the element to be removed
     * @return A new array containing the existing elements except the element
     *         at the specified position.
     * @throws IndexOutOfBoundsException if the index is out of range
     * (index &lt; 0 || index &gt;= array.length), or if the array is {@code null}.
     * @since 2.1
     */
    private static Object remove(final Object array, final int index) {
        final int length = getLength(array);
        if (index < 0 || index >= length) {
            throw new IndexOutOfBoundsException("Index: " + index + ", Length: " + length);
        }

        final Object result = Array.newInstance(array.getClass().getComponentType(), length - 1);
        System.arraycopy(array, 0, result, 0, index);
        if (index < length - 1) {
            System.arraycopy(array, index + 1, result, index, length - index - 1);
        }

        return result;
    }

    /**
     * <p>Removes the element at the specified position from the specified array.
     * All subsequent elements are shifted to the left (subtracts one from
     * their indices).</p>
     *
     * <p>This method returns a new array with the same elements of the input
     * array except the element on the specified position. The component
     * type of the returned array is always the same as that of the input
     * array.</p>
     *
     * <p>If the input array is {@code null}, an IndexOutOfBoundsException
     * will be thrown, because in that case no valid index can be specified.</p>
     *
     * <pre>
     * ArrayUtils.remove(["a"], 0)           = []
     * ArrayUtils.remove(["a", "b"], 0)      = ["b"]
     * ArrayUtils.remove(["a", "b"], 1)      = ["a"]
     * ArrayUtils.remove(["a", "b", "c"], 1) = ["a", "c"]
     * </pre>
     *
     * @param <T> the component type of the array
     * @param array  the array to remove the element from, may not be {@code null}
     * @param index  the position of the element to be removed
     * @return A new array containing the existing elements except the element
     *         at the specified position.
     * @throws IndexOutOfBoundsException if the index is out of range
     * (index &lt; 0 || index &gt;= array.length), or if the array is {@code null}.
     * @since 2.1
     */
    @SuppressWarnings("unchecked") // remove() always creates an array of the same type as its input
    public static <T> T[] remove(final T[] array, final int index) {
        return (T[]) remove((Object) array, index);
    }

}