Java Reference
In-Depth Information
1
// Fig. 16.15: PriorityQueueTest.java
2
// PriorityQueue test program.
3
import
java.util.PriorityQueue;
4
5
public class
PriorityQueueTest
6
{
7
public static void
main(String[] args)
8
{
9
// queue of capacity 11
PriorityQueue<Double> queue =
new
PriorityQueue<>();
10
11
12
// insert elements to queue
queue.offer(
3.2)
;
queue.offer(
9.8
);
queue.offer(
5.4
);
13
14
15
16
17
System.out.print(
"Polling from queue: "
);
18
19
// display elements in queue
20
while
(
queue.size()
>
0
)
21
{
22
System.out.printf(
"%.1f "
,
queue.peek()
);
// view top element
23
queue.poll();
// remove top element
24
}
25
}
26
}
// end class PriorityQueueTest
Polling from queue: 3.2 5.4 9.8
Fig. 16.15
|
PriorityQueue
test program.
A
Set
is an
unordered
Collection
of unique elements (i.e.,
no duplicates
). The collections
framework contains several
Set
implementations, including
HashSet
and
TreeSet
.
Hash-
Set
stores its elements in a
hash table
, and
TreeSet
stores its elements in a
tree
. Hash tables
are presented in Section 16.11. Trees are discussed in Section 21.7.
Figure 16.16 uses a
HashSet
to
remove duplicate strings
from a
List
. Recall that both
List
and
Collection
are generic types, so line 16 creates a
List
that contains
String
objects, and line 20 passes a
Collection
of
String
s to method
printNonDuplicates
.
Method
printNonDuplicates
(lines 24-35) takes a
Collection
argument. Line 27 con-
structs a
HashSet<String>
from the
Collection<String>
argument. By definition,
Set
s
do
not
contain duplicates, so when the
HashSet
is constructed, it
removes any duplicates
in
the
Collection
. Lines 31-32 output elements in the
Set
.
1
// Fig. 16.16: SetTest.java
2
// HashSet used to remove duplicate values from array of strings.
3
import
java.util.List;
4
import
java.util.Arrays;
Fig. 16.16
|
HashSet
used to remove duplicate values from an array of strings. (Part 1 of 2.)
