Returns a hash code for the given JavaBean object
for all the reader methods
using the algorithm suggested in
Item 8 of Effective Java by Joshua Bloch.
Gets the entry corresponding to the specified key; if no such entry
exists, returns the entry for the least key greater than the specified
key; if no such entry exists (i.e., the greatest key in the Tree is less
than the specified key), returns null.
Returns the entry for the greatest key less than the specified key; if no
such entry exists (i.e., the least key in the Tree is greater than the
specified key), returns null.