are these interface arguments ?

[Aftab Hassan]

Hello,
I'm a bit confused about what feature of Java this is. I am doing a bit of Hadoop and this syntax is something I've not seen before.

public class Mapper1 extends MapReduceBase implements Mapper<LongWritable, Text, Text, LongWritable>

Can you tell me what <...> above is, and point me to an online page/tutorial regarding the same?

Thanks.

PS : Kindly note that I respect that this forum is only for Java related queries and not for Hadoop etc. Just thought I'd post it here, since it was a Java question.

[Ulf Dittmer]

That's generics. It has nothing to do with interfaces, specifically.

[Aftab Hassan]

Ulf Dittmer wrote:That's generics. It has nothing to do with interfaces, specifically.

Thanks a lot Ulf Dittmer for the pointer.
Googled and figured out the rest.

Marking the thread as solved.

[Campbell Ritchie]

Who wrote a class with four type parameters?

[Paweł Baczyński]

Campbell Ritchie wrote:Who wrote a class with four type parameters?

Don't know. But I think it is this class from hadoop: Mapper you can found this class' history here ;).
But if this is the class OP meant then this declaration:

public class Mapper1 extends MapReduceBase implements Mapper<LongWritable, Text, Text, LongWritable>

will result in a compile error.
You can't implement a class. Interface only.

Aftab, is full name of your Mapper class org.apache.hadoop.mapreduce.Mapper?

[Aftab Hassan]

Pawel Pawlowicz wrote:Aftab, is full name of your Mapper class org.apache.hadoop.mapreduce.Mapper?

Yes, that's the one.
http://hadoop.apache.org/docs/r2.3.0/api/org/apache/hadoop/mapreduce/Mapper.html