Data Structures and Algorithms in Java[1].pdf - Fulvio Frisone

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The java.util.PriorityQueue Class
There is no priority queue interface built into Java, but Java does include a class,
java.util.PriorityQueue, which implements the java.util.Queue
interface. Instead of adding and removing elements according to the FIFO policy,
however, which is the standard queue policy, the
java.util.PriorityQueue class processes its entries according to a
priority. This priority is defined by a given comparator object, which is passed to
the queue in a constructor, or it is defined by the natural ordering of the elements
being stored in the queue. Even though the java.util.PriorityQueue is
based on the java.util.Queue interface, we can define a simple
correspondence between the methods of this class and our priority queue ADT, as
shown in Table 8.1, assuming we have a class, PQEntry, which implements the
Entry interface.
Table 8.1: Methods of our priority queue ADT and
corresponding methods of class
java.util.PriorityQueue. We assume that the
comparator for PQEntry objects is essentially the
same as the comparator for the keys of the priority
queue. Note that java.util.PriorityQueue has a
pair of methods for its main operation. The two
methods have similar functionality, with minor
differences in the way they deal with boundary
conditions (e.g., trying to remove from an empty
priority queue).
Priority Queue ADT
Classjava.util.PriorityQueue
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