Get the index and last index of an int type value array : Array Sort Search « Collections « Java Tutorial

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/*   Copyright 2004 The Apache Software Foundation
 *
 *   Licensed 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.
 */


import java.lang.reflect.Array;


/**
 * Operations on arrays, primitive arrays (like <code>int[]</code>) and
 * primitive wrapper arrays (like <code>Integer[]</code>).
 * 
 * This class tries to handle <code>null</code> input gracefully.
 * An exception will not be thrown for a <code>null</code>
 * array input. However, an Object array that contains a <code>null</code>
 * element may throw an exception. Each method documents its behaviour.
 *
 * @author Stephen Colebourne
 * @author Moritz Petersen
 * @author <a href="mailto:fredrik@westermarck.com">Fredrik Westermarck</a>
 * @author Nikolay Metchev
 * @author Matthew Hawthorne
 * @author Tim O'Brien
 * @author Pete Gieser
 * @author Gary Gregory
 * @author <a href="mailto:equinus100@hotmail.com">Ashwin S</a>
 * @author Maarten Coene
 * @since 2.0
 * @version $Id: ArrayUtils.java 632503 2008-03-01 00:21:52Z ggregory $
 */
public class Main {
  /**
   * The index value when an element is not found in a list or array: <code>-1</code>.
   * This value is returned by methods in this class and can also be used in comparisons with values returned by
   * various method from {@link java.util.List}.
   */
  public static final int INDEX_NOT_FOUND = -1;

  // int IndexOf
  //-----------------------------------------------------------------------
  /**
   * Finds the index of the given value in the array.
   *
   * This method returns {@link #INDEX_NOT_FOUND} (<code>-1</code>) for a <code>null</code> input array.
   * 
   * @param array  the array to search through for the object, may be <code>null</code>
   * @param valueToFind  the value to find
   * @return the index of the value within the array,
   *  {@link #INDEX_NOT_FOUND} (<code>-1</code>) if not found or <code>null</code> array input
   */
  public static int indexOf(int[] array, int valueToFind) {
      return indexOf(array, valueToFind, 0);
  }

  /**
   * Finds the index of the given value in the array starting at the given index.
   *
   * This method returns {@link #INDEX_NOT_FOUND} (<code>-1</code>) for a <code>null</code> input array.
   *
   * A negative startIndex is treated as zero. A startIndex larger than the array
   * length will return {@link #INDEX_NOT_FOUND} (<code>-1</code>).
   * 
   * @param array  the array to search through for the object, may be <code>null</code>
   * @param valueToFind  the value to find
   * @param startIndex  the index to start searching at
   * @return the index of the value within the array,
   *  {@link #INDEX_NOT_FOUND} (<code>-1</code>) if not found or <code>null</code> array input
   */
  public static int indexOf(int[] array, int valueToFind, int startIndex) {
      if (array == null) {
          return INDEX_NOT_FOUND;
      }
      if (startIndex < 0) {
          startIndex = 0;
      }
      for (int i = startIndex; i < array.length; i++) {
          if (valueToFind == array[i]) {
              return i;
          }
      }
      return INDEX_NOT_FOUND;
  }

  /**
   * Finds the last index of the given value within the array.
   *
   * This method returns {@link #INDEX_NOT_FOUND} (<code>-1</code>) for a <code>null</code> input array.
   * 
   * @param array  the array to travers backwords looking for the object, may be <code>null</code>
   * @param valueToFind  the object to find
   * @return the last index of the value within the array,
   *  {@link #INDEX_NOT_FOUND} (<code>-1</code>) if not found or <code>null</code> array input
   */
  public static int lastIndexOf(int[] array, int valueToFind) {
      return lastIndexOf(array, valueToFind, Integer.MAX_VALUE);
  }

  /**
   * Finds the last index of the given value in the array starting at the given index.
   *
   * This method returns {@link #INDEX_NOT_FOUND} (<code>-1</code>) for a <code>null</code> input array.
   *
   * A negative startIndex will return {@link #INDEX_NOT_FOUND} (<code>-1</code>). A startIndex larger than the
   * array length will search from the end of the array.
   * 
   * @param array  the array to traverse for looking for the object, may be <code>null</code>
   * @param valueToFind  the value to find
   * @param startIndex  the start index to travers backwards from
   * @return the last index of the value within the array,
   *  {@link #INDEX_NOT_FOUND} (<code>-1</code>) if not found or <code>null</code> array input
   */
  public static int lastIndexOf(int[] array, int valueToFind, int startIndex) {
      if (array == null) {
          return INDEX_NOT_FOUND;
      }
      if (startIndex < 0) {
          return INDEX_NOT_FOUND;
      } else if (startIndex >= array.length) {
          startIndex = array.length - 1;
      }
      for (int i = startIndex; i >= 0; i--) {
          if (valueToFind == array[i]) {
              return i;
          }
      }
      return INDEX_NOT_FOUND;
  }

  /**
   * Checks if the value is in the given array.
   *
   * The method returns <code>false</code> if a <code>null</code> array is passed in.
   * 
   * @param array  the array to search through
   * @param valueToFind  the value to find
   * @return <code>true</code> if the array contains the object
   */
  public static boolean contains(int[] array, int valueToFind) {
      return indexOf(array, valueToFind) != INDEX_NOT_FOUND;
  }
}