Hadoop Map Reduce CustomRecordReader Reduce Phase

Question

i am new to hadoop. I successfully created a custom RecordReader and a custom type called "Allineamento" so:

public class Allineamento extends Object implements WritableComparable<Allineamento>

the map phase works and finishes his jobs. When the reduce phase starts i have this exception :

Someone suggests me to insert in "Allineamento" an empty constructor (public Allineamento(){}). Is this the way? And why?

Answer 1

Just add the empty constructor, apparently Hadoop needs the class to have a default constructor, so just add it.

public class Allineamento {
    public Allineamento() {

    }
}

And it should work.