code: /*
   * #%L
   * Simmetrics Core
   * %%
   * Copyright (C) 2014 - 2016 Simmetrics Authors
   * %%
   * 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.
   * #L%
   */
  
  
  package org.simmetrics.tokenizers;
  
  import java.util.List;
  import java.util.Set;
  
  import com.google.common.collect.Multiset;
  
  /**
   * A tokenizer divides an input string into tokens. A tokenizer may not provide
   * a collection containing null.
   * <p>
   * It is recommend that implementations extend {@link AbstractTokenizer}
   * rather then implement this interface.
   */
  public interface Tokenizer {
  
  	/**
  	 * Return tokenized version of a string as a list of tokens.
  	 *
  	 * @param input
  	 *            input string to tokenize
  	 *
  	 * @return List tokenized version of a string
  	 */
  	public List<String> tokenizeToList(String input);
  
  	/**
  	 * Return tokenized version of a string as a multiset of tokens.
  	 *
  	 * @param input
  	 *            input string to tokenize
  	 * @return tokenized version of a string as a multiset
  	 */
  	public Multiset<String> tokenizeToMultiset(String input);
  	
  	/**
  	 * Return tokenized version of a string as a set of tokens.
  	 *
  	 * @param input
  	 *            input string to tokenize
  	 * @return tokenized version of a string as a set
  	 */
  	public Set<String> tokenizeToSet(String input);
  
  }
  