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{{java|AbstractQueue}} is an example of a ''skeletal implementation''.
====BlockingQueue class====▼
=====PriorityQueue class=====▼
The <code>java.util.PriorityQueue</code> class implements <code>java.util.Queue</code>, but also alters it.{{sfn|Bloch|2018|loc=Chapter §9 Item 64: Refer to objects by their interfaces|pp=280-281}} <code>PriorityQueue</code> has an additional {{Javadoc|module=java.base|package=java.util.concurrent|class=PriorityQueue|member=comparator()|text=comparator()|monotype=y}} method.{{sfn|Bloch|2018|loc=Chapter §9 Item 64: Refer to objects by their interfaces|pp=280-281}} Instead of elements being ordered in the order in which they are inserted, they are ordered by priority. The method used to determine priority is either the {{Javadoc|module=java.base|package=java.lang|class=Comparable|member=compareTo(T)|monotype=y}} method in the elements, or a method given in the constructor. The class creates this by using a heap to keep the items sorted.<ref>{{cite web|url=http://docs.oracle.com/javase/7/docs/api/java/util/PriorityQueue.html |title=PriorityQueue (Java Platform SE 7) |publisher=Docs.oracle.com |date=2013-06-06 |access-date=2013-08-16}}</ref>▼
The
'''{{Javadoc|module=java.base|package=java.util.concurrent|class=BlockingQueue|monotype=y}}''' interface extends <code>Queue</code>,{{sfn|Goetz|Peierls|Bloch|Bowbeer|2006|loc=§5.2 Concurrent collections|pp=84-85}} and can be used more flexibly. <code>BlockingQueue</code> works like a regular <code>Queue</code>, but additions to and removals from the <code>BlockingQueue</code> are blocking.{{sfn|Bloch|2018|loc=Chapter §11 Item 78: Synchronize access to shared mutable data|pp=325-329}} If
{{Javadoc|module=java.base|package=java.util|class=Queue|member=remove(java.lang.Object)|text=remove(Object o)|monotype=y}} is called on an empty <code>BlockingQueue</code>, it can be set to wait either a specified time or indefinitely for an item to appear in the <code>BlockingQueue</code>. Similarly, adding an item using the method {{Javadoc|module=java.base|package=java.util|class=Queue|member=add(java.lang.Object)|text=add(Object o)|monotype=y}} is subject to an optional capacity restriction on the <code>BlockingQueue</code>, and the method can wait for space to become available in the <code>BlockingQueue</code> before returning. <code>BlockingQueue</code> interface introduces a method {{Javadoc|module=java.base|package=java.util|class=BlockingQueue|member=take()|text=take()|monotype=y}} which removes and gets the head of the <code>BlockingQueue</code>, and waits until the <code>BlockingQueue</code> is no longer empty if required.<ref>{{cite web|url=http://docs.oracle.com/javase/7/docs/api/java/util/concurrent/BlockingQueue.html |title=BlockingQueue (Java Platform SE 7) |publisher=Docs.oracle.com |date=2013-06-06 |access-date=2013-08-16}}</ref>{{sfn|Bloch|2018|loc=Chapter §11 Item 81: Prefer concurrency utilities to wait and notify|pp=325-329}}
▲====PriorityQueue class====
▲The <code>java.util.PriorityQueue</code> class implements <code>java.util.Queue</code>, but also alters it.{{sfn|Bloch|2018|loc=Chapter §9 Item 64: Refer to objects by their interfaces|pp=280-281}} <code>PriorityQueue</code> has an additional {{Javadoc|module=java.base|package=java.util.concurrent|class=PriorityQueue|member=comparator()|text=comparator()|monotype=y}} method.{{sfn|Bloch|2018|loc=Chapter §9 Item 64: Refer to objects by their interfaces|pp=280-281}} Instead of elements being ordered in the order in which they are inserted, they are ordered by priority. The method used to determine priority is either the {{Javadoc|module=java.base|package=java.lang|class=Comparable|member=compareTo(T)|monotype=y}} method in the elements, or a method given in the constructor. The class creates this by using a heap to keep the items sorted.<ref>{{cite web|url=http://docs.oracle.com/javase/7/docs/api/java/util/PriorityQueue.html |title=PriorityQueue (Java Platform SE 7) |publisher=Docs.oracle.com |date=2013-06-06 |access-date=2013-08-16}}</ref>
===Double-ended queue (Deque) interfaces===
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