A priority queue: the binary heap - Data Structures and Problem Solving Using Java - page 813

private static final int DEFAULT_CAPACITY = 100;

1

2
3 /**
4 * Construct an empty PriorityQueue.
5 */
6 public PriorityQueue( )
7 {
8 currentSize = 0;
9 cmp = null;
10 array = (AnyType[]) new Object[ DEFAULT_CAPACITY + 1 ];
11 }
12
13 /**
14 * Construct an empty PriorityQueue with a specified comparator.
15 */
16 public PriorityQueue( Comparator<? super AnyType> c )
17 {
18 currentSize = 0;
19 cmp = c;
20 array = (AnyType[]) new Object[ DEFAULT_CAPACITY + 1 ];
21 }
22
23
24 /**
25 * Construct a PriorityQueue from another Collection.
26 */
27 public PriorityQueue( Collection<? extends AnyType> coll )
28 {
29 cmp = null;
30 currentSize = coll.size( );
31 array = (AnyType[]) new Object[ ( currentSize + 2 ) * 11 / 10 ];
32
33 int i = 1;
34 for( AnyType item : coll )
35 array[ i++ ] = item;
36 buildHeap( );
37 }

figure 21.5
Constructors for the PriorityQueue class

1 /**
2 * Returns the smallest item in the priority queue.
3 * @return the smallest item.
4 * @throws NoSuchElementException if empty.
5 */
6 public AnyType element( )
7 {
8 if( isEmpty( ) )
9 throw new NoSuchElementException( );
10 return array[ 1 ];
11 }

figure 21.6
The element routine