blocks|key|658401|text|您正在寻找的可能是代替Runnable的Callable<V>接口，并使用Future<V>对象检索值，该对象也允许您等待直到计算出值为止。您可以通过从Executors.newSingleThreadExecutor()获得的ExecutorService来实现此目的。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|658402|public+void+test()+{
++++int+x;
++++ExecutorService+es+=+Executors.newSingleThreadExecutor();
++++Future<Integer>+result+=+es.submit(new+Callable<Integer>()+{
++++++++public+Integer+call()+throws+Exception+{
++++++++++++//+the+other+thread
++++++++++++return+2;
++++++++}
++++});
++++try+{
++++++++x+=+result.get();
++++}+catch+(Exception+e)+{
++++++++//+failed
++++}
++++es.shutdown();
}|code-block|syntax|javascript|658403|entityMap^0|B|8|K|B|11|9|24|Z|36|F|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@$9|N|A|O|B|C]|$9|P|A|Q|B|C]|$9|R|A|S|B|C]|$9|T|A|U|B|C]|$9|V|A|W|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|X|8|@]|D|@]|E|$I|J]]|$1|K|3|-4|5|6|7|Y|8|@]|D|@]|E|$]]]|L|$]]

What you are looking for is probably the <code>Callable&lt;V&gt;</code> interface in place of <code>Runnable</code>, and retrieving the value with a <code>Future&lt;V&gt;</code> object, which also lets you wait until the value has been computed. You can achieve this with an <code>ExecutorService</code>, which you can get from <code>Executors.newSingleThreadExecutor()</code> .

<pre><code>public void test() {
 int x;
 ExecutorService es = Executors.newSingleThreadExecutor();
 Future&lt;Integer&gt; result = es.submit(new Callable&lt;Integer&gt;() {
 public Integer call() throws Exception {
 // the other thread
 return 2;
 }
 });
 try {
 x = result.get();
 } catch (Exception e) {
 // failed
 }
 es.shutdown();
}
</code></pre>

blocks|key|444072|text|您可以使用局部最终变量数组。该变量需要是非基元类型，因此可以使用数组。您还需要同步这两个线程，例如使用CountDownLatch|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|444073|public+void+test()
{+++
++++final+CountDownLatch+latch+=+new+CountDownLatch(1);
++++final+int[]+value+=+new+int[1];
++++Thread+uiThread+=+new+HandlerThread("UIHandler"){
++++++++@Override
++++++++public+void+run(){
++++++++++++value[0]+=+2;
++++++++++++latch.countDown();+//+Release+await()+in+the+test+thread.
++++++++}
++++};
++++uiThread.start();
++++latch.await();+//+Wait+for+countDown()+in+the+UI+thread.+Or+could+uiThread.join();
++++//+value[0]+holds+2+at+this+point.
}|code-block|syntax|javascript|444074|您还可以像这样使用Executor和Callable：|style|CODE|444075|public+void+test()+throws+InterruptedException,+ExecutionException
{+++
++++ExecutorService+executor+=+Executors.newSingleThreadExecutor();
++++Callable<Integer>+callable+=+new+Callable<Integer>()+{
++++++++@Override
++++++++public+Integer+call()+{
++++++++++++return+2;
++++++++}
++++};
++++Future<Integer>+future+=+executor.submit(callable);
++++//+future.get()+returns+2+or+raises+an+exception+if+the+thread+dies,+so+safer
++++executor.shutdown();
}|444076|entityMap|0|LINK|mutability|MUTABLE|url|http://docs.oracle.com/javase/7/docs/api/java/util/concurrent/CountDownLatch.html|1|http://docs.oracle.com/javase/7/docs/api/java/util/concurrent/Executors.html|2|http://docs.oracle.com/javase/7/docs/api/java/util/concurrent/Callable.html^0|1F|E|0|0|0|9|8|I|8|9|8|1|I|8|2|0|0^^$0|@$1|2|3|4|5|6|7|10|8|@]|9|@$A|11|B|12|1|13]]|C|$]]|$1|D|3|E|5|F|7|14|8|@]|9|@]|C|$G|H]]|$1|I|3|J|5|6|7|15|8|@$A|16|B|17|K|L]|$A|18|B|19|K|L]]|9|@$A|1A|B|1B|1|1C]|$A|1D|B|1E|1|1F]]|C|$]]|$1|M|3|N|5|F|7|1G|8|@]|9|@]|C|$G|H]]|$1|O|3|-4|5|6|7|1H|8|@]|9|@]|C|$]]]|P|$Q|$5|R|S|T|C|$U|V]]|W|$5|R|S|T|C|$U|X]]|Y|$5|R|S|T|C|$U|Z]]]]

You can use a local final variable array. The variable needs to be of non-primitive type, so you can use an array. You also need to synchronize the two threads, for example using a <a href="http://docs.oracle.com/javase/7/docs/api/java/util/concurrent/CountDownLatch.html">CountDownLatch</a>:

<pre><code>public void test()
{ 
 final CountDownLatch latch = new CountDownLatch(1);
 final int[] value = new int[1];
 Thread uiThread = new HandlerThread("UIHandler"){
 @Override
 public void run(){
 value[0] = 2;
 latch.countDown(); // Release await() in the test thread.
 }
 };
 uiThread.start();
 latch.await(); // Wait for countDown() in the UI thread. Or could uiThread.join();
 // value[0] holds 2 at this point.
}
</code></pre>

You can also use an <a href="http://docs.oracle.com/javase/7/docs/api/java/util/concurrent/Executors.html"><code>Executor</code></a> and a <a href="http://docs.oracle.com/javase/7/docs/api/java/util/concurrent/Callable.html"><code>Callable</code></a> like this:

<pre><code>public void test() throws InterruptedException, ExecutionException
{ 
 ExecutorService executor = Executors.newSingleThreadExecutor();
 Callable&lt;Integer&gt; callable = new Callable&lt;Integer&gt;() {
 @Override
 public Integer call() {
 return 2;
 }
 };
 Future&lt;Integer&gt; future = executor.submit(callable);
 // future.get() returns 2 or raises an exception if the thread dies, so safer
 executor.shutdown();
}
</code></pre>

blocks|key|444168|text|如果您想要调用方法的值，那么它应该等待线程完成，这使得使用线程有点毫无意义。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|444169|为了直接回答你的问题，这个值可以存储在调用方法和线程都有引用的任何可变对象中。您可以使用外部this，但除了对于琐碎的示例之外，它不会特别有用。|offset|length|style|CODE|444170|对问题中的代码稍加注意:扩展Thread通常是一种糟糕的风格。实际上，不必要地扩展类不是一个好主意。我注意到你的run方法是同步的，因为某些原因。现在，由于本例中的对象是Thread，因此您可以干扰Thread使用其锁的任何内容(在参考实现中，与join有关)。|444171|entityMap^0|0|1A|4|0|E|6|1K|3|2D|6|2R|6|3F|4|0^^$0|@$1|2|3|4|5|6|7|L|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|M|8|@$D|N|E|O|F|G]]|9|@]|A|$]]|$1|H|3|I|5|6|7|P|8|@$D|Q|E|R|F|G]|$D|S|E|T|F|G]|$D|U|E|V|F|G]|$D|W|E|X|F|G]|$D|Y|E|Z|F|G]]|9|@]|A|$]]|$1|J|3|-4|5|6|7|10|8|@]|9|@]|A|$]]]|K|$]]

If you want the value from the calling method, then it should wait for the thread to finish, which makes using threads a bit pointless.

To directly answer you question, the value can be stored in any mutable object both the calling method and the thread both have a reference to. You could use the outer <code>this</code>, but that isn't going to be particularly useful other than for trivial examples.

A little note on the code in the question: Extending <code>Thread</code> is usually poor style. Indeed extending classes unnecessarily is a bad idea. I notice you <code>run</code> method is synchronised for some reason. Now as the object in this case is the <code>Thread</code> you may interfere with whatever <code>Thread</code> uses its lock for (in the reference implementation, something to do with <code>join</code>, IIRC).

blocks|key|658601|text|使用上述答案中描述的Future可以完成这项工作，但由于f.get()会阻塞线程，直到它获得结果，这就违反了并发性。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|658602|最好的解决方案是使用芭乐的ListenableFuture。举个例子：|658603|++++ListenableFuture<Void>+future+=+MoreExecutors.listeningDecorator(Executors.newFixedThreadPool(1,+new+NamedThreadFactory).submit(new+Callable<Void>()
++++{
++++++++@Override
++++++++public+Void+call()+throws+Exception
++++++++{
++++++++++++someBackgroundTask();
++++++++}
++++});
++++Futures.addCallback(future,+new+FutureCallback<Long>()
++++{
++++++++@Override
++++++++public+void+onSuccess(Long+result)
++++++++{
++++++++++++doSomething();
++++++++}

++++++++@Override
++++++++public+void+onFailure(Throwable+t)
++++++++{

++++++++}
++++};|code-block|syntax|javascript|658604|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|K|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|L|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|M|8|@]|9|@]|A|$G|H]]|$1|I|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|J|$]]

Using Future described in above answers does the job, but a bit less significantly as f.get(), blocks the thread until it gets the result, which violates concurrency. 

Best solution is to use Guava's ListenableFuture. An example : 

<pre><code> ListenableFuture&lt;Void&gt; future = MoreExecutors.listeningDecorator(Executors.newFixedThreadPool(1, new NamedThreadFactory).submit(new Callable&lt;Void&gt;()
 {
 @Override
 public Void call() throws Exception
 {
 someBackgroundTask();
 }
 });
 Futures.addCallback(future, new FutureCallback&lt;Long&gt;()
 {
 @Override
 public void onSuccess(Long result)
 {
 doSomething();
 }

 @Override
 public void onFailure(Throwable t)
 {

 }
 };
</code></pre>

blocks|key|444238|text|从Java8开始，我们有了CompletableFuture。就您的情况而言，您可以使用supplyAsync方法在执行后获取结果。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|444239|请找到一些参考here。|444240|++++CompletableFuture<Integer>+completableFuture
++++  =+CompletableFuture.supplyAsync(()+->+yourMethod());

+++completableFuture.get()+//gives+you+the+value|code-block|syntax|javascript|444241|entityMap|0|LINK|mutability|MUTABLE|url|https://www.baeldung.com/java-completablefuture#Processing^0|D|H|18|B|0|7|4|0|0|0^^$0|@$1|2|3|4|5|6|7|U|8|@$9|V|A|W|B|C]|$9|X|A|Y|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|Z|8|@]|D|@$9|10|A|11|1|12]]|E|$]]|$1|H|3|I|5|J|7|13|8|@]|D|@]|E|$K|L]]|$1|M|3|-4|5|6|7|14|8|@]|D|@]|E|$]]]|N|$O|$5|P|Q|R|E|$S|T]]]]

From Java 8 onwards we have <code>CompletableFuture</code>.
On your case, you may use the method <code>supplyAsync</code> to get the result after execution.
Please find some reference <a href="https://www.baeldung.com/java-completablefuture#Processing" rel="nofollow noreferrer">here</a>.
<pre><code> CompletableFuture&lt;Integer&gt; completableFuture
   = CompletableFuture.supplyAsync(() -&gt; yourMethod());

 completableFuture.get() //gives you the value
</code></pre>

blocks|key|444282|text|这是一种更简洁的方法，您只需对现有代码稍作更改即可。目标是从Thread中获得结果。结果并不是真的需要return。取而代之的是，使用回调样式获取结果并进行进一步处理。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|444283|public+class+Test+{

++public+static+void+main(String[]+args)+{
++++String+str+=+args[0];
++++int+count+=+0;

++++Thread+t+=+new+Thread(()+->
++++++someFuncToRun(str,+count,+(value)+->+{
++++++++System.out.println(value);
++++++++return+value;
++++++}));

++++t.start();
++}
++//+Here+I+even+run+a+recursive+method+because+run+things+in+the+
++//+a+thread+sometime+is+to+delegate+those+heavy+lifting+elsewhere
++public+static+String+someFuncToRun(String+str,+int+ctn,+Callback<String>+p)+{
++++%2B%2Bctn;
++++if+(ctn+==+10)+{
++++++System.out.println("End+here");
++++++return+p.cb(str);
++++}
++++System.out.println(ctn+%2B+"+times");
++++return+someFuncToRun(str+%2B+"+%2B1",+ctn,+p);
++}
}

//+The+key+is+here,+this+allow+you+to+pass+a+lambda+callback+to+your+method+
//+update:+use+generic+to+allow+passing+different+type+of+data
//+you+could+event+make+it+<T,S>+so+input+one+type+return+another+type++
interface+Callback<T>+{
++++public+T+cb(T+a);
}|code-block|syntax|javascript|444284|entityMap^0|1F|6|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@$9|N|A|O|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|P|8|@]|D|@]|E|$I|J]]|$1|K|3|-4|5|6|7|Q|8|@]|D|@]|E|$]]]|L|$]]

Here is a cleaner approach, you just need a bit change to your existing code. The goal is to get the result from the the Thread. It doesn't really have to be <code>return</code> a result. Instead, using a callback style to take that result and do further processing.
<pre><code>public class Test {

 public static void main(String[] args) {
 String str = args[0];
 int count = 0;

 Thread t = new Thread(() -&gt;
 someFuncToRun(str, count, (value) -&gt; {
 System.out.println(value);
 return value;
 }));

 t.start();
 }
 // Here I even run a recursive method because run things in the 
 // a thread sometime is to delegate those heavy lifting elsewhere
 public static String someFuncToRun(String str, int ctn, Callback&lt;String&gt; p) {
 ++ctn;
 if (ctn == 10) {
 System.out.println(&quot;End here&quot;);
 return p.cb(str);
 }
 System.out.println(ctn + &quot; times&quot;);
 return someFuncToRun(str + &quot; +1&quot;, ctn, p);
 }
}

// The key is here, this allow you to pass a lambda callback to your method 
// update: use generic to allow passing different type of data
// you could event make it &lt;T,S&gt; so input one type return another type 
interface Callback&lt;T&gt; {
 public T cb(T a);
}

</code></pre>

I have a method with a <code>HandlerThread</code>. A value gets changed inside the <code>Thread</code> and I'd like to return it to the <code>test()</code> method. Is there a way to do this?

<pre><code>public void test()
{ 
 Thread uiThread = new HandlerThread("UIHandler"){
 public synchronized void run(){
 int value; 
 value = 2; //To be returned to test()
 }
 };
 uiThread.start();
}
</code></pre>

Returning value from Thread

我有一个带有HandlerThread的方法。在Thread中更改了一个值，我想将它返回给test()方法。有没有办法做到这一点？public void test(){       Thread uiThread = new HandlerThread("UIHandler"){        public synch...

问从线程返回值
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