Compile Listing 5-6 ( javac CustomClassAndHashSet.java ) and run the
application ( java CustomClassAndHashSet ). You will observe output (similar
to that shown below) that reveals no duplicate elements:
[Saturn, Earth, Uranus, Fomalhaut b, 51 Pegasi b, Venus,
Jupiter, Mercury, Mars, Neptune]
Note LinkedHashSet is a subclass of HashSet that uses a linked list to store
itselements.Asaresult, LinkedHashSet 'siteratorreturnselementsintheorderin
which they were inserted. For example, if Listing 5-4 had specified Set<String>
ss = new LinkedHashSet<>(); ,theapplication'soutputwouldhavebeen ss:
apples pears grapes bananas kiwis null . Also, LinkedHashSet
offers slower performance than HashSet and faster performance than TreeSet .
Chapter 3 introduced youtotraditional enumerated typesandtheir enumreplacement.
(An enum is an enumerated type that is expressed via reserved word enum .) The fol-
lowing example demonstrates the traditional enumerated type:
static final int SUNDAY = 1;
static final int MONDAY = 2;
static final int TUESDAY = 4;
static final int WEDNESDAY = 8;
static final int THURSDAY = 16;
static final int FRIDAY = 32;
static final int SATURDAY = 64;
Although the enum has many advantages over the traditional enumerated type, the
for example, static final int DAYS_OFF = SUNDAY | MONDAY; .
DAYS_OFF is an example of an integer-based, fixed-length bitset , which is a set of
is set to 1, and is absent from the set when the bit is set to 0.
Note An int -basedbitsetcannotcontainmorethan32membersbecause int has
asizeof32bits.Similarly,a long -basedbitsetcannotcontainmorethan64members
because long has a size of 64 bits.