Java Doc for PriorityBlockingQueue.java in  » 6.0-JDK-Core » Collections-Jar-Zip-Logging-regex » java » util » concurrent » Java Source Code / Java DocumentationJava Source Code and Java Documentation

This class and its iterator implement all of the optional methods of the Collection and Iterator interfaces. The Iterator provided in method PriorityBlockingQueue.iterator() is not guaranteed to traverse the elements of the PriorityBlockingQueue in any particular order. If you need ordered traversal, consider using Arrays.sort(pq.toArray()). Also, method drainTo can be used to remove some or all elements in priority order and place them in another collection.

Operations on this class make no guarantees about the ordering of elements with equal priority. If you need to enforce an ordering, you can define custom classes or comparators that use a secondary key to break ties in primary priority values. For example, here is a class that applies first-in-first-out tie-breaking to comparable elements. To use it, you would insert a new FIFOEntry(anEntry) instead of a plain entry object.

 class FIFOEntry<E extends Comparable<? super E>>
 implements Comparable<FIFOEntry<E>> {
 final static AtomicLong seq = new AtomicLong();
 final long seqNum;
 final E entry;
 public FIFOEntry(E entry) {
 seqNum = seq.getAndIncrement();
 this.entry = entry;
 }
 public E getEntry() { return entry; }
 public int compareTo(FIFOEntry<E> other) {
 int res = entry.compareTo(other.entry);
 if (res == 0 && other.entry != this.entry)
 res = (seqNum < other.seqNum ? -1 : 1);
 return res;
 }
 }

This class is a member of the Java Collections Framework.
since:
   1.5
author:
   Doug Lea<
Parameters:
  E - > the type of elements held in this collection

The returned array will be "safe" in that no references to it are maintained by this queue.

If this queue fits in the specified array with room to spare (i.e., the array has more elements than this queue), the element in the array immediately following the end of the queue is set to null.

Like the PriorityBlockingQueue.toArray() method, this method acts as bridge between array-based and collection-based APIs.

The returned array will be "safe" in that no references to it are maintained by this queue. (In other words, this method must allocate a new array). The caller is thus free to modify the returned array.

This method acts as bridge between array-based and collection-based APIs. an array containing all of the elements in this queue

If this queue fits in the specified array with room to spare (i.e., the array has more elements than this queue), the element in the array immediately following the end of the queue is set to null.

Like the PriorityBlockingQueue.toArray() method, this method acts as bridge between array-based and collection-based APIs. Further, this method allows precise control over the runtime type of the output array, and may, under certain circumstances, be used to save allocation costs.

Suppose x is a queue known to contain only strings. The following code can be used to dump the queue into a newly allocated array of String:

 String[] y = x.toArray(new String[0]);