Checks if the String contains only unicode letters. : Unicode « Development « Java Tutorial

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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.
 */

public class Main {

  //-----------------------------------------------------------------------
  /**
   * Checks if the String contains only unicode letters.
   *
   * <code>null</code> will return <code>false</code>.
   * An empty String ("") will return <code>true</code>.
   *
   * <pre>
   * StringUtils.isAlpha(null)   = false
   * StringUtils.isAlpha("")     = true
   * StringUtils.isAlpha("  ")   = false
   * StringUtils.isAlpha("abc")  = true
   * StringUtils.isAlpha("ab2c") = false
   * StringUtils.isAlpha("ab-c") = false
   * </pre>
   *
   * @param str  the String to check, may be null
   * @return <code>true</code> if only contains letters, and is non-null
   */
  public static boolean isAlpha(String str) {
      if (str == null) {
          return false;
      }
      int sz = str.length();
      for (int i = 0; i < sz; i++) {
          if (Character.isLetter(str.charAt(i)) == false) {
              return false;
          }
      }
      return true;
  }
}