3 |
|
/** |
4 |
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* An unbounded priority queue based on a priority heap. This queue orders |
5 |
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* elements according to an order specified at construction time, which is |
6 |
< |
* specified in the same manner as {@link TreeSet} and {@link TreeMap}: elements are ordered |
6 |
> |
* specified in the same manner as {@link TreeSet} and {@link TreeMap}: |
7 |
> |
* elements are ordered |
8 |
|
* either according to their <i>natural order</i> (see {@link Comparable}), or |
9 |
|
* according to a {@link Comparator}, depending on which constructor is used. |
10 |
< |
* The {@link #peek}, {@link #poll}, and {@link #remove} methods return the |
11 |
< |
* minimal element with respect to the specified ordering. If multiple |
12 |
< |
* elements are tied for least value, no guarantees are made as to |
13 |
< |
* which of these elements is returned. |
10 |
> |
* The <em>head</em> of this queue is the least element with respect to the |
11 |
> |
* specified ordering. If multiple elements are tied for least value, the |
12 |
> |
* head is one of those elements. A priority queue does not permit |
13 |
> |
* <tt>null</tt> elements. |
14 |
> |
* |
15 |
> |
* <p>The {@link #remove()} and {@link #poll()} methods remove and |
16 |
> |
* return the head of the queue. |
17 |
> |
* |
18 |
> |
* <p>The {@link #element()} and {@link #peek()} methods return, but do |
19 |
> |
* not delete, the head of the queue. |
20 |
|
* |
21 |
|
* <p>A priority queue has a <i>capacity</i>. The capacity is the |
22 |
|
* size of the array used internally to store the elements on the |
24 |
|
* elements are added to a priority queue, its capacity grows |
25 |
|
* automatically. The details of the growth policy are not specified. |
26 |
|
* |
27 |
< |
*<p>Implementation note: this implementation provides O(log(n)) time |
28 |
< |
*for the insertion methods (<tt>offer</tt>, <tt>poll</tt>, |
29 |
< |
*<tt>remove()</tt> and <tt>add</tt>) methods; linear time for the |
30 |
< |
*<tt>remove(Object)</tt> and <tt>contains(Object)</tt> methods; and |
31 |
< |
*constant time for the retrieval methods (<tt>peek</tt>, |
32 |
< |
*<tt>element</tt>, and <tt>size</tt>). |
27 |
> |
* <p>Implementation note: this implementation provides O(log(n)) time |
28 |
> |
* for the insertion methods (<tt>offer</tt>, <tt>poll</tt>, |
29 |
> |
* <tt>remove()</tt> and <tt>add</tt>) methods; linear time for the |
30 |
> |
* <tt>remove(Object)</tt> and <tt>contains(Object)</tt> methods; and |
31 |
> |
* constant time for the retrieval methods (<tt>peek</tt>, |
32 |
> |
* <tt>element</tt>, and <tt>size</tt>). |
33 |
|
* |
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|
* <p>This class is a member of the |
35 |
|
* <a href="{@docRoot}/../guide/collections/index.html"> |
38 |
|
* @author Josh Bloch |
39 |
|
*/ |
40 |
|
public class PriorityQueue<E> extends AbstractQueue<E> |
41 |
< |
implements Queue<E>, |
42 |
< |
java.io.Serializable { |
41 |
> |
implements Queue<E>, Sorted, java.io.Serializable { |
42 |
> |
|
43 |
|
private static final int DEFAULT_INITIAL_CAPACITY = 11; |
44 |
|
|
45 |
|
/** |
75 |
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private transient int modCount = 0; |
76 |
|
|
77 |
|
/** |
78 |
< |
* Create a new priority queue with the default initial capacity |
78 |
> |
* Create a <tt>PriorityQueue</tt> with the default initial capacity |
79 |
|
* (11) that orders its elements according to their natural |
80 |
|
* ordering (using <tt>Comparable</tt>.) |
81 |
|
*/ |
82 |
|
public PriorityQueue() { |
83 |
< |
this(DEFAULT_INITIAL_CAPACITY); |
83 |
> |
this(DEFAULT_INITIAL_CAPACITY, null); |
84 |
|
} |
85 |
|
|
86 |
|
/** |
87 |
< |
* Create a new priority queue with the specified initial capacity |
87 |
> |
* Create a <tt>PriorityQueue</tt> with the specified initial capacity |
88 |
|
* that orders its elements according to their natural ordering |
89 |
|
* (using <tt>Comparable</tt>.) |
90 |
|
* |
95 |
|
} |
96 |
|
|
97 |
|
/** |
98 |
< |
* Create a new priority queue with the specified initial capacity (11) |
98 |
> |
* Create a <tt>PriorityQueue</tt> with the specified initial capacity |
99 |
|
* that orders its elements according to the specified comparator. |
100 |
|
* |
101 |
|
* @param initialCapacity the initial capacity for this priority queue. |
102 |
|
* @param comparator the comparator used to order this priority queue. |
103 |
+ |
* If <tt>null</tt> then the order depends on the elements' natural |
104 |
+ |
* ordering. |
105 |
|
*/ |
106 |
|
public PriorityQueue(int initialCapacity, Comparator<E> comparator) { |
107 |
|
if (initialCapacity < 1) |
111 |
|
} |
112 |
|
|
113 |
|
/** |
114 |
< |
* Create a new priority queue containing the elements in the specified |
114 |
> |
* Create a <tt>PriorityQueue</tt> containing the elements in the specified |
115 |
|
* collection. The priority queue has an initial capacity of 110% of the |
116 |
|
* size of the specified collection. If the specified collection |
117 |
|
* implements the {@link Sorted} interface, the priority queue will be |
137 |
|
initialCapacity = 1; |
138 |
|
queue = (E[]) new Object[initialCapacity + 1]; |
139 |
|
|
131 |
– |
|
140 |
|
if (initialElements instanceof Sorted) { |
141 |
|
comparator = ((Sorted)initialElements).comparator(); |
142 |
|
for (Iterator<E> i = initialElements.iterator(); i.hasNext(); ) |
151 |
|
// Queue Methods |
152 |
|
|
153 |
|
/** |
154 |
< |
* Remove and return the minimal element from this priority queue |
147 |
< |
* if it contains one or more elements, otherwise return |
148 |
< |
* <tt>null</tt>. The term <i>minimal</i> is defined according to |
149 |
< |
* this priority queue's order. |
154 |
> |
* Add the specified element to this priority queue. |
155 |
|
* |
156 |
< |
* @return the minimal element from this priority queue if it contains |
157 |
< |
* one or more elements, otherwise <tt>null</tt>. |
156 |
> |
* @param element the element to add. |
157 |
> |
* @return <tt>true</tt> |
158 |
> |
* @throws ClassCastException if the specified element cannot be compared |
159 |
> |
* with elements currently in the priority queue according |
160 |
> |
* to the priority queue's ordering. |
161 |
> |
* @throws NullPointerException if the specified element is null. |
162 |
|
*/ |
163 |
+ |
public boolean offer(E element) { |
164 |
+ |
if (element == null) |
165 |
+ |
throw new NullPointerException(); |
166 |
+ |
modCount++; |
167 |
+ |
++size; |
168 |
+ |
|
169 |
+ |
// Grow backing store if necessary |
170 |
+ |
while (size >= queue.length) { |
171 |
+ |
E[] newQueue = (E[]) new Object[2 * queue.length]; |
172 |
+ |
System.arraycopy(queue, 0, newQueue, 0, queue.length); |
173 |
+ |
queue = newQueue; |
174 |
+ |
} |
175 |
+ |
|
176 |
+ |
queue[size] = element; |
177 |
+ |
fixUp(size); |
178 |
+ |
return true; |
179 |
+ |
} |
180 |
+ |
|
181 |
|
public E poll() { |
182 |
|
if (size == 0) |
183 |
|
return null; |
184 |
|
return remove(1); |
185 |
|
} |
186 |
|
|
160 |
– |
/** |
161 |
– |
* Return, but do not remove, the minimal element from the |
162 |
– |
* priority queue, or return <tt>null</tt> if the queue is empty. |
163 |
– |
* The term <i>minimal</i> is defined according to this priority |
164 |
– |
* queue's order. This method returns the same object reference |
165 |
– |
* that would be returned by by the <tt>poll</tt> method. The two |
166 |
– |
* methods differ in that this method does not remove the element |
167 |
– |
* from the priority queue. |
168 |
– |
* |
169 |
– |
* @return the minimal element from this priority queue if it contains |
170 |
– |
* one or more elements, otherwise <tt>null</tt>. |
171 |
– |
*/ |
187 |
|
public E peek() { |
188 |
|
return queue[1]; |
189 |
|
} |
190 |
|
|
191 |
|
// Collection Methods |
192 |
|
|
193 |
+ |
// these first two override just to get the throws docs |
194 |
+ |
|
195 |
|
/** |
196 |
< |
* Removes a single instance of the specified element from this priority |
180 |
< |
* queue, if it is present. Returns true if this collection contained the |
181 |
< |
* specified element (or equivalently, if this collection changed as a |
182 |
< |
* result of the call). |
183 |
< |
* |
184 |
< |
* @param element the element to be removed from this collection, |
185 |
< |
* if present. |
186 |
< |
* @return <tt>true</tt> if this collection changed as a result of the |
187 |
< |
* call |
188 |
< |
* @throws ClassCastException if the specified element cannot be compared |
189 |
< |
* with elements currently in the priority queue according |
190 |
< |
* to the priority queue's ordering. |
191 |
< |
* @throws NullPointerException if the specified element is null. |
196 |
> |
* @throws NullPointerException if the specified element is <tt>null</tt>. |
197 |
|
*/ |
198 |
< |
public boolean remove(Object element) { |
199 |
< |
if (element == null) |
198 |
> |
public boolean add(E element) { |
199 |
> |
return super.add(element); |
200 |
> |
} |
201 |
> |
|
202 |
> |
// /** |
203 |
> |
// * @throws NullPointerException if any element is <tt>null</tt>. |
204 |
> |
// */ |
205 |
> |
// public boolean addAll(Collection c) { |
206 |
> |
// return super.addAll(c); |
207 |
> |
// } |
208 |
> |
|
209 |
> |
/** |
210 |
> |
* @throws NullPointerException if the specified element is <tt>null</tt>. |
211 |
> |
*/ |
212 |
> |
public boolean remove(Object o) { |
213 |
> |
if (o == null) |
214 |
|
throw new NullPointerException(); |
215 |
|
|
216 |
|
if (comparator == null) { |
217 |
|
for (int i = 1; i <= size; i++) { |
218 |
< |
if (((Comparable)queue[i]).compareTo(element) == 0) { |
218 |
> |
if (((Comparable)queue[i]).compareTo(o) == 0) { |
219 |
|
remove(i); |
220 |
|
return true; |
221 |
|
} |
222 |
|
} |
223 |
|
} else { |
224 |
|
for (int i = 1; i <= size; i++) { |
225 |
< |
if (comparator.compare(queue[i], (E) element) == 0) { |
225 |
> |
if (comparator.compare(queue[i], (E)o) == 0) { |
226 |
|
remove(i); |
227 |
|
return true; |
228 |
|
} |
305 |
|
} |
306 |
|
|
307 |
|
/** |
289 |
– |
* Add the specified element to this priority queue. |
290 |
– |
* |
291 |
– |
* @param element the element to add. |
292 |
– |
* @return true |
293 |
– |
* @throws ClassCastException if the specified element cannot be compared |
294 |
– |
* with elements currently in the priority queue according |
295 |
– |
* to the priority queue's ordering. |
296 |
– |
* @throws NullPointerException if the specified element is null. |
297 |
– |
*/ |
298 |
– |
public boolean offer(E element) { |
299 |
– |
if (element == null) |
300 |
– |
throw new NullPointerException(); |
301 |
– |
modCount++; |
302 |
– |
++size; |
303 |
– |
|
304 |
– |
// Grow backing store if necessary |
305 |
– |
while (size >= queue.length) { |
306 |
– |
E[] newQueue = (E[]) new Object[2 * queue.length]; |
307 |
– |
System.arraycopy(queue, 0, newQueue, 0, queue.length); |
308 |
– |
queue = newQueue; |
309 |
– |
} |
310 |
– |
|
311 |
– |
queue[size] = element; |
312 |
– |
fixUp(size); |
313 |
– |
return true; |
314 |
– |
} |
315 |
– |
|
316 |
– |
/** |
308 |
|
* Remove all elements from the priority queue. |
309 |
|
*/ |
310 |
|
public void clear() { |
397 |
|
} |
398 |
|
} |
399 |
|
|
409 |
– |
/** |
410 |
– |
* Returns the comparator associated with this priority queue, or |
411 |
– |
* <tt>null</tt> if it uses its elements' natural ordering. |
412 |
– |
* |
413 |
– |
* @return the comparator associated with this priority queue, or |
414 |
– |
* <tt>null</tt> if it uses its elements' natural ordering. |
415 |
– |
*/ |
400 |
|
public Comparator comparator() { |
401 |
|
return comparator; |
402 |
|
} |
443 |
|
} |
444 |
|
|
445 |
|
} |
446 |
+ |
|