Trivial Description
/** The class is responsible for choosing the desired number of targets * for placing block replicas. * The replica placement strategy is that if the writer is on a datanode, * the 1st replica is placed on the local machine, * otherwise a random datanode. The 2nd replica is placed on a datanode * that is on a different rack. The 3rd replica is placed on a datanode * which is on the same rack as the **first replca**. */
That should read "second replica". The test cases confirm that this is the behavior, as well as the docs.