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| SUMMARY: NESTED | FIELD | CONSTR | <A HREF="#method_summary">METHOD</A></FONT></TD> |
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| <H2> |
| <FONT SIZE="-1"> |
| org.apache.openjpa.lib.util.concurrent</FONT> |
| <BR> |
| Interface Queue</H2> |
| <DL> |
| <DT><B>All Superinterfaces:</B> <DD><A HREF="http://java.sun.com/j2se/1.5.0/docs/api/java/util/Collection.html" title="class or interface in java.util">Collection</A>, <A HREF="http://java.sun.com/j2se/1.5.0/docs/api/java/lang/Iterable.html" title="class or interface in java.lang">Iterable</A></DD> |
| </DL> |
| <DL> |
| <DT><B>All Known Implementing Classes:</B> <DD><A HREF="../../../../../../org/apache/openjpa/lib/util/concurrent/ConcurrentLinkedQueue.html" title="class in org.apache.openjpa.lib.util.concurrent">ConcurrentLinkedQueue</A></DD> |
| </DL> |
| <HR> |
| <DL> |
| <DT><PRE>public interface <B>Queue</B><DT>extends <A HREF="http://java.sun.com/j2se/1.5.0/docs/api/java/util/Collection.html" title="class or interface in java.util">Collection</A></DL> |
| </PRE> |
| |
| <P> |
| A collection designed for holding elements prior to processing. |
| Besides basic <A HREF="http://java.sun.com/j2se/1.5.0/docs/api/java/util/Collection.html" title="class or interface in java.util"><CODE>Collection</CODE></A> operations, |
| queues provide additional insertion, extraction, and inspection |
| operations. Each of these methods exists in two forms: one throws |
| an exception if the operation fails, the other returns a special |
| value(either <tt>null</tt> or <tt>false</tt>, depending on the |
| operation). The latter form of the insert operation is designed |
| specifically for use with capacity-restricted <tt>Queue</tt> |
| implementations; in most implementations, insert operations cannot fail. |
| |
| |
| <table BORDER CELLPADDING=3 CELLSPACING=1> |
| <tr> |
| <td></td> |
| <td ALIGN=CENTER><em>Throws exception</em></td> |
| <td ALIGN=CENTER><em>Returns special value</em></td> |
| </tr> |
| <tr> |
| <td><b>Insert</b></td> |
| <td><A HREF="../../../../../../org/apache/openjpa/lib/util/concurrent/Queue.html#add(java.lang.Object)"><CODE>add(e)</CODE></A></td> |
| <td><A HREF="../../../../../../org/apache/openjpa/lib/util/concurrent/Queue.html#offer(java.lang.Object)"><CODE>offer(e)</CODE></A></td> |
| </tr> |
| <tr> |
| <td><b>Remove</b></td> |
| <td><A HREF="../../../../../../org/apache/openjpa/lib/util/concurrent/Queue.html#remove()"><CODE>remove()</CODE></A></td> |
| <td><A HREF="../../../../../../org/apache/openjpa/lib/util/concurrent/Queue.html#poll()"><CODE>poll()</CODE></A></td> |
| </tr> |
| <tr> |
| <td><b>Examine</b></td> |
| <td><A HREF="../../../../../../org/apache/openjpa/lib/util/concurrent/Queue.html#element()"><CODE>element()</CODE></A></td> |
| <td><A HREF="../../../../../../org/apache/openjpa/lib/util/concurrent/Queue.html#peek()"><CODE>peek()</CODE></A></td> |
| </tr> |
| </table> Queues typically, but do not necessarily, order elements in a |
| FIFO(first-in-first-out) manner. Among the exceptions are |
| priority queues, which order elements according to a supplied |
| comparator, or the elements' natural ordering, and LIFO queues(or |
| stacks) which order the elements LIFO(last-in-first-out). |
| Whatever the ordering used, the <em>head</em> of the queue is that |
| element which would be removed by a call to <A HREF="../../../../../../org/apache/openjpa/lib/util/concurrent/Queue.html#remove()"><CODE>remove()</CODE></A> or |
| <A HREF="../../../../../../org/apache/openjpa/lib/util/concurrent/Queue.html#poll()"><CODE>poll()</CODE></A>. In a FIFO queue, all new elements are inserted at |
| the <em> tail</em> of the queue. Other kinds of queues may use |
| different placement rules. Every <tt>Queue</tt> implementation |
| must specify its ordering properties. |
| The <A HREF="../../../../../../org/apache/openjpa/lib/util/concurrent/Queue.html#offer(java.lang.Object)"><CODE>offer</CODE></A> method inserts an element if possible, |
| otherwise returning <tt>false</tt>. This differs from the <A HREF="http://java.sun.com/j2se/1.5.0/docs/api/java/util/Collection.html#add(E)" title="class or interface in java.util"><CODE>Collection.add</CODE></A> method, which can fail to |
| add an element only by throwing an unchecked exception. The |
| <tt>offer</tt> method is designed for use when failure is a normal, |
| rather than exceptional occurrence, for example, in fixed-capacity |
| (or "bounded") queues. |
| The <A HREF="../../../../../../org/apache/openjpa/lib/util/concurrent/Queue.html#remove()"><CODE>remove()</CODE></A> and <A HREF="../../../../../../org/apache/openjpa/lib/util/concurrent/Queue.html#poll()"><CODE>poll()</CODE></A> methods remove and |
| return the head of the queue. |
| Exactly which element is removed from the queue is a |
| function of the queue's ordering policy, which differs from |
| implementation to implementation. The <tt>remove()</tt> and |
| <tt>poll()</tt> methods differ only in their behavior when the |
| queue is empty: the <tt>remove()</tt> method throws an exception, |
| while the <tt>poll()</tt> method returns <tt>null</tt>. |
| The <A HREF="../../../../../../org/apache/openjpa/lib/util/concurrent/Queue.html#element()"><CODE>element()</CODE></A> and <A HREF="../../../../../../org/apache/openjpa/lib/util/concurrent/Queue.html#peek()"><CODE>peek()</CODE></A> methods return, but do |
| not remove, the head of the queue. |
| The <tt>Queue</tt> interface does not define the <i>blocking queue |
| methods</i>, which are common in concurrent programming. These methods, |
| which wait for elements to appear or for space to become available, are |
| defined in the <CODE>edu.emory.mathcs.backport.java.util.concurrent.BlockingQueue</CODE> interface, which |
| extends this interface. |
| |
| <tt>Queue</tt> implementations generally do not allow insertion |
| of <tt>null</tt> elements, although some implementations, such as |
| <A HREF="http://java.sun.com/j2se/1.5.0/docs/api/java/util/LinkedList.html" title="class or interface in java.util"><CODE>LinkedList</CODE></A>, do not prohibit insertion of <tt>null</tt>. |
| Even in the implementations that permit it, <tt>null</tt> should |
| not be inserted into a <tt>Queue</tt>, as <tt>null</tt> is also |
| used as a special return value by the <tt>poll</tt> method to |
| indicate that the queue contains no elements. |
| |
| <tt>Queue</tt> implementations generally do not define |
| element-based versions of methods <tt>equals</tt> and |
| <tt>hashCode</tt> but instead inherit the identity based versions |
| from class <tt>Object</tt>, because element-based equality is not |
| always well-defined for queues with the same elements but different |
| ordering properties. |
| This interface is a member of the |
| <a href="../../../../../../../guide/collections/index.html"> |
| Java Collections Framework</a>. |
| <P> |
| |
| <P> |
| <DL> |
| <DT><B>Since:</B></DT> |
| <DD>1.5</DD> |
| <DT><B>Author:</B></DT> |
| <DD>Doug Lea</DD> |
| <DT><B>See Also:</B><DD><A HREF="http://java.sun.com/j2se/1.5.0/docs/api/java/util/Collection.html" title="class or interface in java.util"><CODE>Collection</CODE></A>, |
| <A HREF="http://java.sun.com/j2se/1.5.0/docs/api/java/util/LinkedList.html" title="class or interface in java.util"><CODE>LinkedList</CODE></A>, |
| <CODE>PriorityQueue</CODE>, |
| <CODE>edu.emory.mathcs.backport.java.util.concurrent.LinkedBlockingQueue</CODE>, |
| <CODE>edu.emory.mathcs.backport.java.util.concurrent.BlockingQueue</CODE>, |
| <CODE>edu.emory.mathcs.backport.java.util.concurrent.ArrayBlockingQueue</CODE>, |
| <CODE>edu.emory.mathcs.backport.java.util.concurrent.LinkedBlockingQueue</CODE>, |
| <CODE>edu.emory.mathcs.backport.java.util.concurrent.PriorityBlockingQueue</CODE></DL> |
| <HR> |
| |
| <P> |
| |
| <!-- ========== METHOD SUMMARY =========== --> |
| |
| <A NAME="method_summary"><!-- --></A> |
| <TABLE BORDER="1" WIDTH="100%" CELLPADDING="3" CELLSPACING="0" SUMMARY=""> |
| <TR BGCOLOR="#CCCCFF" CLASS="TableHeadingColor"> |
| <TH ALIGN="left" COLSPAN="2"><FONT SIZE="+2"> |
| <B>Method Summary</B></FONT></TH> |
| </TR> |
| <TR BGCOLOR="white" CLASS="TableRowColor"> |
| <TD ALIGN="right" VALIGN="top" WIDTH="1%"><FONT SIZE="-1"> |
| <CODE> boolean</CODE></FONT></TD> |
| <TD><CODE><B><A HREF="../../../../../../org/apache/openjpa/lib/util/concurrent/Queue.html#add(java.lang.Object)">add</A></B>(<A HREF="http://java.sun.com/j2se/1.5.0/docs/api/java/lang/Object.html" title="class or interface in java.lang">Object</A> e)</CODE> |
| |
| <BR> |
| Inserts the specified element into this queue if it is possible to do so |
| immediately without violating capacity restrictions, returning |
| <tt>true</tt> upon success and throwing an <tt>IllegalStateException</tt> |
| if no space is currently available.</TD> |
| </TR> |
| <TR BGCOLOR="white" CLASS="TableRowColor"> |
| <TD ALIGN="right" VALIGN="top" WIDTH="1%"><FONT SIZE="-1"> |
| <CODE> <A HREF="http://java.sun.com/j2se/1.5.0/docs/api/java/lang/Object.html" title="class or interface in java.lang">Object</A></CODE></FONT></TD> |
| <TD><CODE><B><A HREF="../../../../../../org/apache/openjpa/lib/util/concurrent/Queue.html#element()">element</A></B>()</CODE> |
| |
| <BR> |
| Retrieves, but does not remove, the head of this queue.</TD> |
| </TR> |
| <TR BGCOLOR="white" CLASS="TableRowColor"> |
| <TD ALIGN="right" VALIGN="top" WIDTH="1%"><FONT SIZE="-1"> |
| <CODE> boolean</CODE></FONT></TD> |
| <TD><CODE><B><A HREF="../../../../../../org/apache/openjpa/lib/util/concurrent/Queue.html#offer(java.lang.Object)">offer</A></B>(<A HREF="http://java.sun.com/j2se/1.5.0/docs/api/java/lang/Object.html" title="class or interface in java.lang">Object</A> e)</CODE> |
| |
| <BR> |
| Inserts the specified element into this queue if it is possible to do |
| so immediately without violating capacity restrictions.</TD> |
| </TR> |
| <TR BGCOLOR="white" CLASS="TableRowColor"> |
| <TD ALIGN="right" VALIGN="top" WIDTH="1%"><FONT SIZE="-1"> |
| <CODE> <A HREF="http://java.sun.com/j2se/1.5.0/docs/api/java/lang/Object.html" title="class or interface in java.lang">Object</A></CODE></FONT></TD> |
| <TD><CODE><B><A HREF="../../../../../../org/apache/openjpa/lib/util/concurrent/Queue.html#peek()">peek</A></B>()</CODE> |
| |
| <BR> |
| Retrieves, but does not remove, the head of this queue, |
| or returns <tt>null</tt> if this queue is empty.</TD> |
| </TR> |
| <TR BGCOLOR="white" CLASS="TableRowColor"> |
| <TD ALIGN="right" VALIGN="top" WIDTH="1%"><FONT SIZE="-1"> |
| <CODE> <A HREF="http://java.sun.com/j2se/1.5.0/docs/api/java/lang/Object.html" title="class or interface in java.lang">Object</A></CODE></FONT></TD> |
| <TD><CODE><B><A HREF="../../../../../../org/apache/openjpa/lib/util/concurrent/Queue.html#poll()">poll</A></B>()</CODE> |
| |
| <BR> |
| Retrieves and removes the head of this queue, |
| or returns <tt>null</tt> if this queue is empty.</TD> |
| </TR> |
| <TR BGCOLOR="white" CLASS="TableRowColor"> |
| <TD ALIGN="right" VALIGN="top" WIDTH="1%"><FONT SIZE="-1"> |
| <CODE> <A HREF="http://java.sun.com/j2se/1.5.0/docs/api/java/lang/Object.html" title="class or interface in java.lang">Object</A></CODE></FONT></TD> |
| <TD><CODE><B><A HREF="../../../../../../org/apache/openjpa/lib/util/concurrent/Queue.html#remove()">remove</A></B>()</CODE> |
| |
| <BR> |
| Retrieves and removes the head of this queue.</TD> |
| </TR> |
| </TABLE> |
| <A NAME="methods_inherited_from_class_java.util.Collection"><!-- --></A> |
| <TABLE BORDER="1" WIDTH="100%" CELLPADDING="3" CELLSPACING="0" SUMMARY=""> |
| <TR BGCOLOR="#EEEEFF" CLASS="TableSubHeadingColor"> |
| <TH ALIGN="left"><B>Methods inherited from interface java.util.<A HREF="http://java.sun.com/j2se/1.5.0/docs/api/java/util/Collection.html" title="class or interface in java.util">Collection</A></B></TH> |
| </TR> |
| <TR BGCOLOR="white" CLASS="TableRowColor"> |
| <TD><CODE><A HREF="http://java.sun.com/j2se/1.5.0/docs/api/java/util/Collection.html#addAll(java.util.Collection)" title="class or interface in java.util">addAll</A>, <A HREF="http://java.sun.com/j2se/1.5.0/docs/api/java/util/Collection.html#clear()" title="class or interface in java.util">clear</A>, <A HREF="http://java.sun.com/j2se/1.5.0/docs/api/java/util/Collection.html#contains(java.lang.Object)" title="class or interface in java.util">contains</A>, <A HREF="http://java.sun.com/j2se/1.5.0/docs/api/java/util/Collection.html#containsAll(java.util.Collection)" title="class or interface in java.util">containsAll</A>, <A HREF="http://java.sun.com/j2se/1.5.0/docs/api/java/util/Collection.html#equals(java.lang.Object)" title="class or interface in java.util">equals</A>, <A HREF="http://java.sun.com/j2se/1.5.0/docs/api/java/util/Collection.html#hashCode()" title="class or interface in java.util">hashCode</A>, <A HREF="http://java.sun.com/j2se/1.5.0/docs/api/java/util/Collection.html#isEmpty()" title="class or interface in java.util">isEmpty</A>, <A HREF="http://java.sun.com/j2se/1.5.0/docs/api/java/util/Collection.html#iterator()" title="class or interface in java.util">iterator</A>, <A HREF="http://java.sun.com/j2se/1.5.0/docs/api/java/util/Collection.html#remove(java.lang.Object)" title="class or interface in java.util">remove</A>, <A HREF="http://java.sun.com/j2se/1.5.0/docs/api/java/util/Collection.html#removeAll(java.util.Collection)" title="class or interface in java.util">removeAll</A>, <A HREF="http://java.sun.com/j2se/1.5.0/docs/api/java/util/Collection.html#retainAll(java.util.Collection)" title="class or interface in java.util">retainAll</A>, <A HREF="http://java.sun.com/j2se/1.5.0/docs/api/java/util/Collection.html#size()" title="class or interface in java.util">size</A>, <A HREF="http://java.sun.com/j2se/1.5.0/docs/api/java/util/Collection.html#toArray()" title="class or interface in java.util">toArray</A>, <A HREF="http://java.sun.com/j2se/1.5.0/docs/api/java/util/Collection.html#toArray(T[])" title="class or interface in java.util">toArray</A></CODE></TD> |
| </TR> |
| </TABLE> |
| |
| <P> |
| |
| <!-- ============ METHOD DETAIL ========== --> |
| |
| <A NAME="method_detail"><!-- --></A> |
| <TABLE BORDER="1" WIDTH="100%" CELLPADDING="3" CELLSPACING="0" SUMMARY=""> |
| <TR BGCOLOR="#CCCCFF" CLASS="TableHeadingColor"> |
| <TH ALIGN="left" COLSPAN="1"><FONT SIZE="+2"> |
| <B>Method Detail</B></FONT></TH> |
| </TR> |
| </TABLE> |
| |
| <A NAME="add(java.lang.Object)"><!-- --></A><H3> |
| add</H3> |
| <PRE> |
| boolean <B>add</B>(<A HREF="http://java.sun.com/j2se/1.5.0/docs/api/java/lang/Object.html" title="class or interface in java.lang">Object</A> e)</PRE> |
| <DL> |
| <DD>Inserts the specified element into this queue if it is possible to do so |
| immediately without violating capacity restrictions, returning |
| <tt>true</tt> upon success and throwing an <tt>IllegalStateException</tt> |
| if no space is currently available. |
| <P> |
| <DD><DL> |
| <DT><B>Specified by:</B><DD><CODE><A HREF="http://java.sun.com/j2se/1.5.0/docs/api/java/util/Collection.html#add(E)" title="class or interface in java.util">add</A></CODE> in interface <CODE><A HREF="http://java.sun.com/j2se/1.5.0/docs/api/java/util/Collection.html" title="class or interface in java.util">Collection</A></CODE></DL> |
| </DD> |
| <DD><DL> |
| <DT><B>Parameters:</B><DD><CODE>e</CODE> - the element to add |
| <DT><B>Returns:</B><DD><tt>true</tt> (as specified by <A HREF="http://java.sun.com/j2se/1.5.0/docs/api/java/util/Collection.html#add(E)" title="class or interface in java.util"><CODE>Collection.add(E)</CODE></A>) |
| <DT><B>Throws:</B> |
| <DD><CODE><A HREF="http://java.sun.com/j2se/1.5.0/docs/api/java/lang/IllegalStateException.html" title="class or interface in java.lang">IllegalStateException</A></CODE> - if the element cannot be added at this |
| time due to capacity restrictions |
| <DD><CODE><A HREF="http://java.sun.com/j2se/1.5.0/docs/api/java/lang/ClassCastException.html" title="class or interface in java.lang">ClassCastException</A></CODE> - if the class of the specified element |
| prevents it from being added to this queue |
| <DD><CODE><A HREF="http://java.sun.com/j2se/1.5.0/docs/api/java/lang/NullPointerException.html" title="class or interface in java.lang">NullPointerException</A></CODE> - if the specified element is null and |
| this queue not permit null elements |
| <DD><CODE><A HREF="http://java.sun.com/j2se/1.5.0/docs/api/java/lang/IllegalArgumentException.html" title="class or interface in java.lang">IllegalArgumentException</A></CODE> - if some property of this element |
| prevents it from being added to this queue</DL> |
| </DD> |
| </DL> |
| <HR> |
| |
| <A NAME="offer(java.lang.Object)"><!-- --></A><H3> |
| offer</H3> |
| <PRE> |
| boolean <B>offer</B>(<A HREF="http://java.sun.com/j2se/1.5.0/docs/api/java/lang/Object.html" title="class or interface in java.lang">Object</A> e)</PRE> |
| <DL> |
| <DD>Inserts the specified element into this queue if it is possible to do |
| so immediately without violating capacity restrictions. |
| When using a capacity-restricted queue, this method is generally |
| preferable to <A HREF="../../../../../../org/apache/openjpa/lib/util/concurrent/Queue.html#add(java.lang.Object)"><CODE>add(java.lang.Object)</CODE></A>, which can fail to insert an element only |
| by throwing an exception. |
| <P> |
| <DD><DL> |
| </DL> |
| </DD> |
| <DD><DL> |
| <DT><B>Parameters:</B><DD><CODE>e</CODE> - the element to add |
| <DT><B>Returns:</B><DD><tt>true</tt> if the element was added to this queue, else |
| <tt>false</tt> |
| <DT><B>Throws:</B> |
| <DD><CODE><A HREF="http://java.sun.com/j2se/1.5.0/docs/api/java/lang/ClassCastException.html" title="class or interface in java.lang">ClassCastException</A></CODE> - if the class of the specified element |
| prevents it from being added to this queue |
| <DD><CODE><A HREF="http://java.sun.com/j2se/1.5.0/docs/api/java/lang/NullPointerException.html" title="class or interface in java.lang">NullPointerException</A></CODE> - if the specified element is null and |
| this queue does not permit null elements |
| <DD><CODE><A HREF="http://java.sun.com/j2se/1.5.0/docs/api/java/lang/IllegalArgumentException.html" title="class or interface in java.lang">IllegalArgumentException</A></CODE> - if some property of this element |
| prevents it from being added to this queue</DL> |
| </DD> |
| </DL> |
| <HR> |
| |
| <A NAME="remove()"><!-- --></A><H3> |
| remove</H3> |
| <PRE> |
| <A HREF="http://java.sun.com/j2se/1.5.0/docs/api/java/lang/Object.html" title="class or interface in java.lang">Object</A> <B>remove</B>()</PRE> |
| <DL> |
| <DD>Retrieves and removes the head of this queue. This method differs |
| from <A HREF="../../../../../../org/apache/openjpa/lib/util/concurrent/Queue.html#poll()"><CODE>poll</CODE></A> only in that it throws an exception if this |
| queue is empty. is empty. |
| <P> |
| <DD><DL> |
| </DL> |
| </DD> |
| <DD><DL> |
| |
| <DT><B>Returns:</B><DD>the head of this queue |
| <DT><B>Throws:</B> |
| <DD><CODE><A HREF="http://java.sun.com/j2se/1.5.0/docs/api/java/util/NoSuchElementException.html" title="class or interface in java.util">NoSuchElementException</A></CODE> - if this queue is empty</DL> |
| </DD> |
| </DL> |
| <HR> |
| |
| <A NAME="poll()"><!-- --></A><H3> |
| poll</H3> |
| <PRE> |
| <A HREF="http://java.sun.com/j2se/1.5.0/docs/api/java/lang/Object.html" title="class or interface in java.lang">Object</A> <B>poll</B>()</PRE> |
| <DL> |
| <DD>Retrieves and removes the head of this queue, |
| or returns <tt>null</tt> if this queue is empty. |
| <P> |
| <DD><DL> |
| </DL> |
| </DD> |
| <DD><DL> |
| |
| <DT><B>Returns:</B><DD>the head of this queue, or <tt>null</tt> if this queue is empty</DL> |
| </DD> |
| </DL> |
| <HR> |
| |
| <A NAME="element()"><!-- --></A><H3> |
| element</H3> |
| <PRE> |
| <A HREF="http://java.sun.com/j2se/1.5.0/docs/api/java/lang/Object.html" title="class or interface in java.lang">Object</A> <B>element</B>()</PRE> |
| <DL> |
| <DD>Retrieves, but does not remove, the head of this queue. This method |
| differs from <A HREF="../../../../../../org/apache/openjpa/lib/util/concurrent/Queue.html#peek()"><CODE>peek</CODE></A> only in that it throws an exception |
| if this queue is empty. |
| <P> |
| <DD><DL> |
| </DL> |
| </DD> |
| <DD><DL> |
| |
| <DT><B>Returns:</B><DD>the head of this queue |
| <DT><B>Throws:</B> |
| <DD><CODE><A HREF="http://java.sun.com/j2se/1.5.0/docs/api/java/util/NoSuchElementException.html" title="class or interface in java.util">NoSuchElementException</A></CODE> - if this queue is empty</DL> |
| </DD> |
| </DL> |
| <HR> |
| |
| <A NAME="peek()"><!-- --></A><H3> |
| peek</H3> |
| <PRE> |
| <A HREF="http://java.sun.com/j2se/1.5.0/docs/api/java/lang/Object.html" title="class or interface in java.lang">Object</A> <B>peek</B>()</PRE> |
| <DL> |
| <DD>Retrieves, but does not remove, the head of this queue, |
| or returns <tt>null</tt> if this queue is empty. |
| <P> |
| <DD><DL> |
| </DL> |
| </DD> |
| <DD><DL> |
| |
| <DT><B>Returns:</B><DD>the head of this queue, or <tt>null</tt> if this queue is empty</DL> |
| </DD> |
| </DL> |
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