Question:

I am using Majority voting combination rule in weka. There are 4 classifiers in total. I am wondering what will happen if there is a tie in the number of votes

Weka API : ".....the random number generator used for breaking ties in majority voting..". See :http://fiji.sc/javadoc/weka/classifiers/meta/Vote.html

If you are interested in code , this is how they do it:

// Resolve the ties according to a uniform random distribution

int majorityIndex = majorityIndexes.get(m_Random .nextInt(majorityIndexes.size()));