how sequence of chained jars in spark.(driver/executor).extraClassPath matters

[Richard Xin]

so let's say I have chained path in 
spark.driver.extraClassPath/spark.executor.extraClassPath such as 
/path1/*:/path2/*, and I have different versions of the same jar under those 2 
directories, how spark pick the version of jar to use, from /path1/*?

Thanks.