source: sample/hadoop-0.16/tw/org/nchc/tuple/ArrayListWritableComparable.java @ 64

/*
 * Cloud9: A MapReduce Library for Hadoop
 * 
 * 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.
 */

package tw.org.nchc.tuple;

import java.io.DataInput;
import java.io.DataOutput;
import java.io.IOException;
import java.util.ArrayList;
import org.apache.hadoop.io.WritableComparable;

/**
 * <p>
 * Class that represents an array list in Hadoop's data type system. It extends ArrayList class, 
 * hence supports all services provided by ArrayList.
 * Elements in the list must be homogeneous and must implement Hadoop's Writable interface. 
 * This class, combined with {@link Tuple}, allows the user to
 * define arbitrarily complex data structures.
 * </p>
 * 
 * @see Tuple
 * @param <E>
 *            type of list element
 */

public class ArrayListWritableComparable<E extends WritableComparable> extends ArrayList<E> implements WritableComparable{

    private static final long serialVersionUID = 1L;

  /**
   * Creates an ArrayListWritable object.
   */
  public ArrayListWritableComparable() {
    super();
  }
  
  /**
   * Creates an ArrayListWritableComparable object from a regular ArrayList.
   */
  public ArrayListWritableComparable(ArrayList<E> array) {
    super(array);
  }

  
  
  /**
   * Deserializes the array.
   * 
   * @param in
   *            source for raw byte representation
   */
  @SuppressWarnings("unchecked")
  public void readFields(DataInput in) throws IOException {

    this.clear();

    int numFields = in.readInt();
    if(numFields==0) return;
    String className = in.readUTF();
    E obj;
    try {
      Class c = Class.forName(className);
      for (int i = 0; i < numFields; i++) {
        obj = (E) c.newInstance();
        obj.readFields(in);
        this.add(obj);
      }

    } catch (ClassNotFoundException e) {
      e.printStackTrace();
    } catch (IllegalAccessException e) {
      e.printStackTrace();
    } catch (InstantiationException e) {
      e.printStackTrace();
    }
  }

  /**
   * Serializes this Tuple.
   * 
   * @param out
   *            where to write the raw byte representation
   */
  public void write(DataOutput out) throws IOException {
    out.writeInt(this.size());
    if(size()==0) return;
    E obj=get(0);
    
    out.writeUTF(obj.getClass().getCanonicalName());

    for (int i = 0; i < size(); i++) {
      obj = get(i);
      if (obj == null) {
        throw new IOException("Cannot serialize null fields!");
      }
      obj.write(out);
    }
  }
  
  /**
   * <p>
   * Defines a natural sort order for the ListWritable class. Following
   * standard convention, this method returns a value less than zero, a value
   * greater than zero, or zero if this ListWritable should be sorted before,
   * sorted after, or is equal to <code>obj</code>. The sort order is
   * defined as follows:
   * </p>
   * 
   * <ul>
   * <li>Each element in the list is compared sequentially from first to
   * last.</li>
   * <li>Lists are sorted with respect to the natural order of the current
   * list element under consideration, by calling its <code>compareTo</code>
   * method.</li>
   * <li>If the current list elements are equal, the next set of elements are
   * considered.</li>
   * <li>If all compared elements are equal, but lists are different lengths,
   * the shorter list is sorted first.</li>
   * <li>If all list elements are equal and the lists are equal in length,
   * then the lists are considered equal</li>
   * </ul>
   * 
   * @return a value less than zero, a value greater than zero, or zero if
   *         this Tuple should be sorted before, sorted after, or is equal to
   *         <code>obj</code>.
   */
  public int compareTo(Object obj) {
    ArrayListWritableComparable<?> that = (ArrayListWritableComparable<?>) obj;

    // iterate through the fields
    for (int i = 0; i < this.size(); i++) {
      // sort shorter list first
      if (i >= that.size())
        return 1;

      @SuppressWarnings("unchecked")
      Comparable<Object> thisField = this.get(i);
      @SuppressWarnings("unchecked")
      Comparable<Object> thatField = that.get(i);

      if (thisField.equals(thatField)) {
        // if we're down to the last field, sort shorter list first
        if (i == this.size() - 1) {
          if (this.size() > that.size())
            return 1;

          if (this.size() < that.size())
            return -1;
        }
        // otherwise, move to next field
      } else {
        return thisField.compareTo(thatField);
      }
    }

    return 0;
  }


  /**
   * Generates human-readable String representation of this ArrayList.
   * 
   * @return human-readable String representation of this ArrayList
   */
  public String toString() {
    StringBuffer sb = new StringBuffer();
    sb.append("[");
    for (int i = 0; i < this.size(); i++){
      if (i != 0)
        sb.append(", ");
      sb.append(this.get(i));
    }
    sb.append("]");

    return sb.toString();
  }
  
}