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Queue (OpenJPA 1.0.1 API) | |
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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> | |
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<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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