Re: Looking for correct way to implements WritableComparable in Hadoop-0.17

[Tom White <to...@cloudera.com>]

Hi Kun,

The book's code is for 0.20.0. In Hadoop 0.17.x WritableComparable was
not generic, so you need a declaration like:

public class IntPair implements WritableComparable {

}

And the compareTo() method should look like this:

public int compareTo(Object o) {
   IntPair ip = (IntPair) o;
   int cmp = compare(first, ip.first);
   if (cmp != 0) {
     return cmp;
   }
   return compare(second, ip.second);
 }

Finally, if you are using Java 5 you should remove the @Override annotations.

Cheers,
Tom

On Sun, Jun 21, 2009 at 1:16 AM, Kunsheng Chen <ke...@yahoo.com> wrote:
>
> Hello everyone,
>
> I am writing my own Comparator inherits from WritableComparable.
>
> I got the folliowing code from "Hadoop definitive guide", which is not working at all, it reminds me "WritableComparable does not take parameter". The book might be using Hadoop-0.21
>
> I also tried the old method for 0.18 version as below:
>
> http://hadoop.apache.org/core/docs/r0.18.3/api/org/apache/hadoop/io/WritableComparable.html
>
> but it will reminds me "hasn't implement compareTo method", which actually I did.
>
> I am wondering if I have to reinstall the hadoop again (I prefer not) or there was any old way to do it.
>
>
> Any idea is well appreciated!
>
> -Kun
>
> --------------------------------------------------
>
> import java.io.*;
>
> import org.apache.hadoop.io.*;
>
> public class IntPair implements WritableComparable<IntPair> {
>
>  private int first;
>  private int second;
>  private Text third;
>
>  public IntPair(int first, int second, Text third) {
>    set(first, second, third);
>  }
>
>  public void set(int first, int second, Text third) {
>    this.first = first;
>    this.second = second;
>    this.third = third;
>  }
>
>  public int getFirst() {
>    return first;
>  }
>
>  public int getSecond() {
>    return second;
>  }
>
>  public Text getThird() {
>
>    return third;
>  }
>
>  @Override
>  public void write(DataOutput out) throws IOException {
>    out.writeInt(first);
>    out.writeInt(second);
>    third.write(out);
>  }
>
>  @Override
>  public void readFields(DataInput in) throws IOException {
>    first = in.readInt();
>    second = in.readInt();
>    // Redundant
>    third.readFields(in);
>
>  }
>
>  @Override
>  public int hashCode() {
>    return first * 163 + second + third.hashCode();
>  }
>
>  @Override
>  public boolean equals(Object o) {
>    if (o instanceof IntPair) {
>      IntPair ip = (IntPair) o;
>      return first == ip.first && second == ip.second && third.equals(ip.third);
>    }
>    return false;
>  }
>  @Override
>  public String toString() {
>    return first + "\t" + second + "\t" + third;
>  }
>
>  @Override
>  public int compareTo(IntPair ip) {
>    int cmp = compare(first, ip.first);
>    if (cmp != 0) {
>      return cmp;
>    }
>    return compare(second, ip.second);
>  }
>
>  /**
>   * Convenience method for comparing two ints.
>   */
>  public static int compare(int a, int b) {
>    return (a < b ? -1 : (a == b ? 0 : 1));
>  }
>
> }
>
> ------------------------------------------------
>
>
>