content: package backtype.storm.tuple;
  
  import java.util.ArrayList;
  import java.util.Arrays;
  import java.util.HashMap;
  import java.util.Iterator;
  import java.util.List;
  import java.util.Map;
  import java.io.Serializable;
  
  public class Fields implements Iterable<String>, Serializable {
      private List<String> _fields;
      private Map<String, Integer> _index = new HashMap<String, Integer>();
      
      public Fields(String... fields) {
          this(Arrays.asList(fields));
      }
      
      public Fields(List<String> fields) {
          _fields = new ArrayList<String>(fields);
          index();
      }
      
      public List<Object> select(Fields selector, List<Object> tuple) {
          List<Object> ret = new ArrayList<Object>(selector.size());
          for(String s: selector) {
              ret.add(tuple.get(_index.get(s)));
          }
          return ret;
      }
  
      public List<String> toList() {
          return new ArrayList<String>(_fields);
      }
      
      public int size() {
          return _fields.size();
      }
  
      public String get(int index) {
          return _fields.get(index);
      }
  
      public Iterator<String> iterator() {
          return _fields.iterator();
      }
      
      public int fieldIndex(String field) {
          Integer ret = _index.get(field);
          if(ret==null) {
              throw new IllegalArgumentException(field + " does not exist");
          }
          return ret;
      }
      
      private void index() {
          for(int i=0; i<_fields.size(); i++) {
              _index.put(_fields.get(i), i);
          }
      }
  }