Checks whether the String contains only digit characters. : String vs Char Array « Data Type « Java Tutorial

import java.math.BigDecimal;
import java.math.BigInteger;

 * 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
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * See the License for the specific language governing permissions and
 * limitations under the License.

 * Provides extra functionality for Java Number classes.
 * @author <a href="">Rand McNeely</a>
 * @author Stephen Colebourne
 * @author <a href="">Steve Downey</a>
 * @author Eric Pugh
 * @author Phil Steitz
 * @since 1.0
 * @version $Id: 488819 2006-12-19 21:50:04Z bayard $
public class Main {
   * Checks whether the <code>String</code> contains only
   * digit characters.
   * <code>Null</code> and empty String will return
   * <code>false</code>.
   * @param str  the <code>String</code> to check
   * @return <code>true</code> if str contains only unicode numeric
  public static boolean isDigits(String str) {
      if ((str == null) || (str.length() == 0)) {
          return false;
      for (int i = 0; i < str.length(); i++) {
          if (!Character.isDigit(str.charAt(i))) {
              return false;
      return true;

2.28.String vs Char Array
2.28.1.Demonstrates the charAt and getChars
2.28.2.Converting Char array to String
2.28.3.Creating Character Arrays From String Objects
2.28.4.Copy characters from string into char Array
2.28.5.Creating String Objects From Character Arrays String(textArray, 9, 3): Creating String Objects From certain part of a character Array
2.28.7.Creating String Objects From Character Arrays using String.copyValueOf()
2.28.8.Creating a string from a subset of the array elements
2.28.9.Extracting a substring as an array of characters using the method getChars()
2.28.10.Using the Collection-Based for Loop with a String: Counting all vowels in a string
2.28.11.Construct one String from another.
2.28.12.demonstrates getChars( ):
2.28.13.implements CharSequence
2.28.14.Removes spaces (char <= 32) from end of this String with escape, handling null by returning null
2.28.15.Removes spaces (char <= 32) from end of this String, handling null by returning null
2.28.16.Swaps the case of a String changing upper and title case to lower case, and lower case to upper case.
2.28.17.Deletes all whitespaces from a String as defined by Character.isWhitespace(char).
2.28.18.Checks whether the String contains only digit characters.
2.28.19.Checks that the String does not contain certain characters.