Hadoop mapper constructor, when and how?
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Ok, so I tried to run my program and this error showed up:

java.lang.RuntimeException: java.lang.NoSuchMethodException: org.(..).SimpleMapReducePricing$SimplePricingMapper.<init>()

which means that I have to initialize my mapper with a constructor, right?
So, my question is why do I have to do it, (since I haven't seen it in any example) and how can I do it in a simple (noob) way?
I am using the new api, and my piece of code is the following: 

        public class SimplePricingMapper 
	    extends Mapper<Object, Text, Text, DoubleWritable>
        {   public void map(Object key, Text value, Context context
            ) throws IOException, InterruptedException {

and so on...

p.s. I saw a similar question, but I must admit that the answers confused me more. 
Thanks!