Java array join to String with String separator

public class Main {
  public static void main(String[] argv) throws Exception {
    Object[] array = new String[] { "CSS", "HTML", "Java", null, "demo2s.com", "Javascript 123" };
    System.out.println(join(array, "/"));
  }//www .  jav  a 2s .  c om

  /**
   * <p>
   * Joins the elements of the provided array into a single String containing the
   * provided list of elements.
   * </p>
   *
   * <p>
   * No delimiter is added before or after the list. A <code>null</code> separator
   * is the same as an empty String (""). Null objects or empty strings within the
   * array are represented by empty strings.
   * </p>
   *
   * <pre>
   * StringUtil.join(null, *)                = null
   * StringUtil.join([], *)                  = ""
   * StringUtil.join([null], *)              = ""
   * StringUtil.join(["a", "b", "c"], "--")  = "a--b--c"
   * StringUtil.join(["a", "b", "c"], null)  = "abc"
   * StringUtil.join(["a", "b", "c"], "")    = "abc"
   * StringUtil.join([null, "", "a"], ',')   = ",,a"
   * </pre>
   *
   * @param array
   *          the array of values to join together, may be null
   * @param separator
   *          the separator character to use, null treated as ""
   * @return the joined String, <code>null</code> if null array input
   */
  public static String join(Object[] array, String separator) {
    if (array == null) {
      return null;
    }
    return join(array, separator, 0, array.length);
  }

  /**
   * <p>
   * Joins the elements of the provided array into a single String containing the
   * provided list of elements.
   * </p>
   *
   * <p>
   * No delimiter is added before or after the list. A <code>null</code> separator
   * is the same as an empty String (""). Null objects or empty strings within the
   * array are represented by empty strings.
   * </p>
   *
   * <pre>
   * StringUtil.join(null, *)                = null
   * StringUtil.join([], *)                  = ""
   * StringUtil.join([null], *)              = ""
   * StringUtil.join(["a", "b", "c"], "--")  = "a--b--c"
   * StringUtil.join(["a", "b", "c"], null)  = "abc"
   * StringUtil.join(["a", "b", "c"], "")    = "abc"
   * StringUtil.join([null, "", "a"], ',')   = ",,a"
   * </pre>
   *
   * @param array
   *          the array of values to join together, may be null
   * @param separator
   *          the separator character to use, null treated as ""
   * @param startIndex
   *          the first index to start joining from. It is an error to pass in an
   *          end index past the end of the array
   * @param endIndex
   *          the index to stop joining from (exclusive). It is an error to pass
   *          in an end index past the end of the array
   * @return the joined String, <code>null</code> if null array input
   */
  public static String join(Object[] array, String separator, int startIndex, int endIndex) {
    if (array == null) {
      return null;
    }
    if (separator == null) {
      separator = EMPTY;
    }

    // endIndex - startIndex > 0: Len = NofStrings *(len(firstString) +
    // len(separator))
    // (Assuming that all Strings are roughly equally long)
    int bufSize = (endIndex - startIndex);
    if (bufSize <= 0) {
      return EMPTY;
    }

    bufSize *= ((array[startIndex] == null ? 16 : array[startIndex].toString().length()) + separator.length());

    StringBuffer buf = new StringBuffer(bufSize);

    for (int i = startIndex; i < endIndex; i++) {
      if (i > startIndex) {
        buf.append(separator);
      }
      if (array[i] != null) {
        buf.append(array[i]);
      }
    }
    return buf.toString();
  }

  public static final String EMPTY = "";
}

/*
 * 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.
 */