Collections and Generics - SCJP Sun Certified Programmer for Java Platform SE6 - page 477

Understand natural ordering vs. comparators. Classes that implement Comparable are
said to have a natural ordering. If a class does not have a natural ordering, use a separate
Comparator object to sort and search instances of the class. The Comparator interface
declares the compare method that returns an int . The return value is a negative integer,
zero, or a positive integer if the fi rst argument is less than, equal to, or greater than the sec-
ond, respectively.
Understand the difference between == and equals . The comparison operator == returns
true if the two references being compared point to the same object. The equals method
compares two objects and uses business logic. If you override equals , make sure you also
override the hashCode method in such a way that two equal objects produce the same hash
code.
Understand the behavior and usage of the sort and binarySearch methods. You should
be able to understand code that uses the sort and binarySearch methods of the Collec-
tions (for lists) and Arrays (for arrays) classes. The Collections class defi nes two static
sort methods: one for natural-order sorting and one for comparator sorting of lists. The
Collections class also defi nes two static binarySearch methods, and the list must be
sorted before it is searched. The Arrays class contains two overloaded sort methods for
each type of array, which provides for both natural-order and comparator sorting. Simi-
larly, the Arrays class contains binarySearch methods for searching the various types of
arrays, and an array must be sorted before it is searched.