I figured it out on my own. I have stored my own implementation of DefaultSimilarity under /dist/ folder in solr. Then i add <lib dir="../../../dist/org/apache/lucene/search/similarities/" regex=".*\.jar"/> to my solrconfig.xml and everything works fine.
package org.apache.lucene.search.similarities;
import org.apache.lucene.index.FieldInvertState;
import org.apache.lucene.search.similarities.DefaultSimilarity;
public class MyNewSimilarityClass extends DefaultSimilarity {
@Override
public float coord(int overlap, int maxOverlap) {
return 1.0f;
}
@Override
public float idf(long docFreq, long numDocs) {
return 1.0f;
}
@Override
public float lengthNorm(FieldInvertState arg0) {
return 1.0f;
}
@Override
public float tf(float freq) {
return 1.0f;
}
}