package org.apache.hadoop.io;

import java.io.DataOutput;
import java.io.DataInput;
import java.io.IOException;

public interface Writable {
  /** 
   * Serialize the fields of this object to <code>out</code>.
   * 
   * @param out <code>DataOuput</code> to serialize this object into.
   * @throws IOException
   */
  void write(DataOutput out) throws IOException;

  /** 
   * Deserialize the fields of this object from <code>in</code>.  
   * 
   * <p>For efficiency, implementations should attempt to re-use storage in the 
   * existing object where possible.</p>
   * 
   * @param in <code>DataInput</code> to deseriablize this object from.
   * @throws IOException
   */
  void readFields(DataInput in) throws IOException;
}
 

package com.yoyzhou.weibo;

import java.io.DataInput;
import java.io.DataOutput;
import java.io.IOException;
import org.apache.hadoop.io.VLongWritable;
import org.apache.hadoop.io.Writable;

/**
 *This MyWritable class demonstrates how to write a custom Writable class 
 *
 **/
public class MyWritable implements Writable{
		
		
	private VLongWritable field1;
	private VLongWritable field2;
		
	public MyWritable(){
		this.set(new VLongWritable(), new VLongWritable());
	}
		
		
	public MyWritable(VLongWritable fld1, VLongWritable fld2){
			
		this.set(fld1, fld2);
			
	}
		
	public void set(VLongWritable fld1, VLongWritable fld2){
		//make sure the smaller field is always put as field1
		if(fld1.get() <= fld2.get()){
			this.field1 = fld1;
			this.field2 = fld2;
		}else{
				
			this.field1 = fld2;
			this.field2 = fld1;
		}
		}
				
	//How to write and read MyWritable fields from DataOutput and DataInput stream
	@Override
	public void write(DataOutput out) throws IOException {
			
		field1.write(out);
		field2.write(out);
	}

	@Override
	public void readFields(DataInput in) throws IOException {
			
		field1.readFields(in);
		field2.readFields(in);
	}

	/** Returns true if <code>o</code> is a MyWritable with the same values. */
	@Override
	public boolean equals(Object o) {
		 if (!(o instanceof MyWritable))
		    return false;
		
		    MyWritable other = (MyWritable)o;
		    return field1.equals(other.field1) && field2.equals(other.field2);
		
	}
		
	@Override
	public int hashCode(){
			
		return field1.hashCode() * 163 + field2.hashCode();
	}
		
	@Override
	public String toString() {
		return field1.toString() + "\t" + field2.toString();
	}
		
}