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<div class="subTitle">edu.emory.mathcs.backport.java.util.concurrent</div>
<h2 title="Interface Future" class="title">Interface Future</h2>
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<dt>All Known Subinterfaces:</dt>
<dd><a href="../../../../../../../edu/emory/mathcs/backport/java/util/concurrent/RunnableFuture.html" title="interface in edu.emory.mathcs.backport.java.util.concurrent">RunnableFuture</a>, <a href="../../../../../../../edu/emory/mathcs/backport/java/util/concurrent/RunnableScheduledFuture.html" title="interface in edu.emory.mathcs.backport.java.util.concurrent">RunnableScheduledFuture</a>, <a href="../../../../../../../edu/emory/mathcs/backport/java/util/concurrent/ScheduledFuture.html" title="interface in edu.emory.mathcs.backport.java.util.concurrent">ScheduledFuture</a></dd>
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<dl>
<dt>All Known Implementing Classes:</dt>
<dd><a href="../../../../../../../edu/emory/mathcs/backport/java/util/concurrent/FutureTask.html" title="class in edu.emory.mathcs.backport.java.util.concurrent">FutureTask</a></dd>
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<pre>public interface <span class="strong">Future</span></pre>
<div class="block">A <tt>Future</tt> represents the result of an asynchronous
computation. Methods are provided to check if the computation is
complete, to wait for its completion, and to retrieve the result of
the computation. The result can only be retrieved using method
<tt>get</tt> when the computation has completed, blocking if
necessary until it is ready. Cancellation is performed by the
<tt>cancel</tt> method. Additional methods are provided to
determine if the task completed normally or was cancelled. Once a
computation has completed, the computation cannot be cancelled.
If you would like to use a <tt>Future</tt> for the sake
of cancellability but not provide a usable result, you can
declare types of the form <tt>Future<?></tt> and
return <tt>null</tt> as a result of the underlying task.
<p>
<b>Sample Usage</b> (Note that the following classes are all
made-up.) <p>
<pre>
interface ArchiveSearcher { String search(String target); }
class App {
ExecutorService executor = ...
ArchiveSearcher searcher = ...
void showSearch(final String target)
throws InterruptedException {
Future<String> future
= executor.submit(new Callable<String>() {
public String call() {
return searcher.search(target);
}});
displayOtherThings(); // do other things while searching
try {
displayText(future.get()); // use future
} catch (ExecutionException ex) { cleanup(); return; }
}
}
</pre>
The <a href="../../../../../../../edu/emory/mathcs/backport/java/util/concurrent/FutureTask.html" title="class in edu.emory.mathcs.backport.java.util.concurrent"><code>FutureTask</code></a> class is an implementation of <tt>Future</tt> that
implements <tt>Runnable</tt>, and so may be executed by an <tt>Executor</tt>.
For example, the above construction with <tt>submit</tt> could be replaced by:
<pre>
FutureTask<String> future =
new FutureTask<String>(new Callable<String>() {
public String call() {
return searcher.search(target);
}});
executor.execute(future);
</pre>
<p>Memory consistency effects: Actions taken by the asynchronous computation
<a href="package-summary.html#MemoryVisibility"> <i>happen-before</i></a>
actions following the corresponding <code>Future.get()</code> in another thread.</div>
<dl><dt><span class="strong">Since:</span></dt>
<dd>1.5</dd>
<dt><span class="strong">Author:</span></dt>
<dd>Doug Lea</dd>
<dt><span class="strong">See Also:</span></dt><dd><a href="../../../../../../../edu/emory/mathcs/backport/java/util/concurrent/FutureTask.html" title="class in edu.emory.mathcs.backport.java.util.concurrent"><code>FutureTask</code></a>,
<a href="../../../../../../../edu/emory/mathcs/backport/java/util/concurrent/Executor.html" title="interface in edu.emory.mathcs.backport.java.util.concurrent"><code>Executor</code></a></dd></dl>
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<h3>Method Summary</h3>
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<caption><span>Methods</span><span class="tabEnd"> </span></caption>
<tr>
<th class="colFirst" scope="col">Modifier and Type</th>
<th class="colLast" scope="col">Method and Description</th>
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<tr class="altColor">
<td class="colFirst"><code>boolean</code></td>
<td class="colLast"><code><strong><a href="../../../../../../../edu/emory/mathcs/backport/java/util/concurrent/Future.html#cancel(boolean)">cancel</a></strong>(boolean mayInterruptIfRunning)</code>
<div class="block">Attempts to cancel execution of this task.</div>
</td>
</tr>
<tr class="rowColor">
<td class="colFirst"><code>java.lang.Object</code></td>
<td class="colLast"><code><strong><a href="../../../../../../../edu/emory/mathcs/backport/java/util/concurrent/Future.html#get()">get</a></strong>()</code>
<div class="block">Waits if necessary for the computation to complete, and then
retrieves its result.</div>
</td>
</tr>
<tr class="altColor">
<td class="colFirst"><code>java.lang.Object</code></td>
<td class="colLast"><code><strong><a href="../../../../../../../edu/emory/mathcs/backport/java/util/concurrent/Future.html#get(long, edu.emory.mathcs.backport.java.util.concurrent.TimeUnit)">get</a></strong>(long timeout,
<a href="../../../../../../../edu/emory/mathcs/backport/java/util/concurrent/TimeUnit.html" title="class in edu.emory.mathcs.backport.java.util.concurrent">TimeUnit</a> unit)</code>
<div class="block">Waits if necessary for at most the given time for the computation
to complete, and then retrieves its result, if available.</div>
</td>
</tr>
<tr class="rowColor">
<td class="colFirst"><code>boolean</code></td>
<td class="colLast"><code><strong><a href="../../../../../../../edu/emory/mathcs/backport/java/util/concurrent/Future.html#isCancelled()">isCancelled</a></strong>()</code>
<div class="block">Returns <tt>true</tt> if this task was cancelled before it completed
normally.</div>
</td>
</tr>
<tr class="altColor">
<td class="colFirst"><code>boolean</code></td>
<td class="colLast"><code><strong><a href="../../../../../../../edu/emory/mathcs/backport/java/util/concurrent/Future.html#isDone()">isDone</a></strong>()</code>
<div class="block">Returns <tt>true</tt> if this task completed.</div>
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<h4>cancel</h4>
<pre>boolean cancel(boolean mayInterruptIfRunning)</pre>
<div class="block">Attempts to cancel execution of this task. This attempt will
fail if the task has already completed, has already been cancelled,
or could not be cancelled for some other reason. If successful,
and this task has not started when <tt>cancel</tt> is called,
this task should never run. If the task has already started,
then the <tt>mayInterruptIfRunning</tt> parameter determines
whether the thread executing this task should be interrupted in
an attempt to stop the task.
<p>After this method returns, subsequent calls to <a href="../../../../../../../edu/emory/mathcs/backport/java/util/concurrent/Future.html#isDone()"><code>isDone()</code></a> will
always return <tt>true</tt>. Subsequent calls to <a href="../../../../../../../edu/emory/mathcs/backport/java/util/concurrent/Future.html#isCancelled()"><code>isCancelled()</code></a>
will always return <tt>true</tt> if this method returned <tt>true</tt>.</div>
<dl><dt><span class="strong">Parameters:</span></dt><dd><code>mayInterruptIfRunning</code> - <tt>true</tt> if the thread executing this
task should be interrupted; otherwise, in-progress tasks are allowed
to complete</dd>
<dt><span class="strong">Returns:</span></dt><dd><tt>false</tt> if the task could not be cancelled,
typically because it has already completed normally;
<tt>true</tt> otherwise</dd></dl>
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<h4>isCancelled</h4>
<pre>boolean isCancelled()</pre>
<div class="block">Returns <tt>true</tt> if this task was cancelled before it completed
normally.</div>
<dl><dt><span class="strong">Returns:</span></dt><dd><tt>true</tt> if this task was cancelled before it completed</dd></dl>
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<h4>isDone</h4>
<pre>boolean isDone()</pre>
<div class="block">Returns <tt>true</tt> if this task completed.
Completion may be due to normal termination, an exception, or
cancellation -- in all of these cases, this method will return
<tt>true</tt>.</div>
<dl><dt><span class="strong">Returns:</span></dt><dd><tt>true</tt> if this task completed</dd></dl>
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<h4>get</h4>
<pre>java.lang.Object get()
throws java.lang.InterruptedException,
<a href="../../../../../../../edu/emory/mathcs/backport/java/util/concurrent/ExecutionException.html" title="class in edu.emory.mathcs.backport.java.util.concurrent">ExecutionException</a></pre>
<div class="block">Waits if necessary for the computation to complete, and then
retrieves its result.</div>
<dl><dt><span class="strong">Returns:</span></dt><dd>the computed result</dd>
<dt><span class="strong">Throws:</span></dt>
<dd><code><a href="../../../../../../../edu/emory/mathcs/backport/java/util/concurrent/CancellationException.html" title="class in edu.emory.mathcs.backport.java.util.concurrent">CancellationException</a></code> - if the computation was cancelled</dd>
<dd><code><a href="../../../../../../../edu/emory/mathcs/backport/java/util/concurrent/ExecutionException.html" title="class in edu.emory.mathcs.backport.java.util.concurrent">ExecutionException</a></code> - if the computation threw an
exception</dd>
<dd><code>java.lang.InterruptedException</code> - if the current thread was interrupted
while waiting</dd></dl>
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<h4>get</h4>
<pre>java.lang.Object get(long timeout,
<a href="../../../../../../../edu/emory/mathcs/backport/java/util/concurrent/TimeUnit.html" title="class in edu.emory.mathcs.backport.java.util.concurrent">TimeUnit</a> unit)
throws java.lang.InterruptedException,
<a href="../../../../../../../edu/emory/mathcs/backport/java/util/concurrent/ExecutionException.html" title="class in edu.emory.mathcs.backport.java.util.concurrent">ExecutionException</a>,
<a href="../../../../../../../edu/emory/mathcs/backport/java/util/concurrent/TimeoutException.html" title="class in edu.emory.mathcs.backport.java.util.concurrent">TimeoutException</a></pre>
<div class="block">Waits if necessary for at most the given time for the computation
to complete, and then retrieves its result, if available.</div>
<dl><dt><span class="strong">Parameters:</span></dt><dd><code>timeout</code> - the maximum time to wait</dd><dd><code>unit</code> - the time unit of the timeout argument</dd>
<dt><span class="strong">Returns:</span></dt><dd>the computed result</dd>
<dt><span class="strong">Throws:</span></dt>
<dd><code><a href="../../../../../../../edu/emory/mathcs/backport/java/util/concurrent/CancellationException.html" title="class in edu.emory.mathcs.backport.java.util.concurrent">CancellationException</a></code> - if the computation was cancelled</dd>
<dd><code><a href="../../../../../../../edu/emory/mathcs/backport/java/util/concurrent/ExecutionException.html" title="class in edu.emory.mathcs.backport.java.util.concurrent">ExecutionException</a></code> - if the computation threw an
exception</dd>
<dd><code>java.lang.InterruptedException</code> - if the current thread was interrupted
while waiting</dd>
<dd><code><a href="../../../../../../../edu/emory/mathcs/backport/java/util/concurrent/TimeoutException.html" title="class in edu.emory.mathcs.backport.java.util.concurrent">TimeoutException</a></code> - if the wait timed out</dd></dl>
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