blocks|key|695379|text|在这个简单的示例中，您只需在两个方法签名中的public之后添加synchronized作为修饰符。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|695380|更复杂的场景需要其他东西。|695381|entityMap^0|M|6|W|C|0|0^^$0|@$1|2|3|4|5|6|7|J|8|@$9|K|A|L|B|C]|$9|M|A|N|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|O|8|@]|D|@]|E|$]]|$1|H|3|-4|5|6|7|P|8|@]|D|@]|E|$]]]|I|$]]

In this simple example you can just put <code>synchronized</code> as a modifier after <code>public</code> in both method signatures.

More complex scenarios require other stuff.

blocks|key|695487|text|使用synchronized关键字。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|695488|class+sample+{
++++private+String+msg=null;

++++public+synchronized+void+newmsg(String+x){
++++++++msg=x;
++++}

++++public+synchronized+string+getmsg(){
++++++++String+temp=msg;
++++++++msg=null;
++++++++return+msg;
++++}
}|code-block|syntax|javascript|695489|在方法上使用synchronized关键字将要求线程获得sample实例上的锁。因此，如果任何一个线程在newmsg()中，则没有其他线程能够获得sample实例上的锁，即使它试图调用getmsg()。|695490|另一方面，如果您的方法执行长时间运行的操作，使用synchronized方法可能会成为一个瓶颈-所有线程，即使它们想要调用该对象中可能交错的其他方法，也仍然必须等待。|695491|在您的简单示例中，可以使用同步方法，因为您实际上有两个不应该交错的方法。但是，在不同的情况下，使用锁对象进行同步可能更有意义，如Joh+Skeet的答案所示。|695492|entityMap^0|2|C|0|0|6|C|S|6|1G|8|21|6|2K|8|0|O|C|0|0^^$0|@$1|2|3|4|5|6|7|S|8|@$9|T|A|U|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|V|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|W|8|@$9|X|A|Y|B|C]|$9|Z|A|10|B|C]|$9|11|A|12|B|C]|$9|13|A|14|B|C]|$9|15|A|16|B|C]]|D|@]|E|$]]|$1|M|3|N|5|6|7|17|8|@$9|18|A|19|B|C]]|D|@]|E|$]]|$1|O|3|P|5|6|7|1A|8|@]|D|@]|E|$]]|$1|Q|3|-4|5|6|7|1B|8|@]|D|@]|E|$]]]|R|$]]

Use the <code>synchronized</code> keyword.

<pre><code>class sample {
 private String msg=null;

 public synchronized void newmsg(String x){
 msg=x;
 }

 public synchronized string getmsg(){
 String temp=msg;
 msg=null;
 return msg;
 }
}
</code></pre>

Using the <code>synchronized</code> keyword on the methods will require threads to obtain a lock on the instance of <code>sample</code>. Thus, if any one thread is in <code>newmsg()</code>, no other thread will be able to get a lock on the instance of <code>sample</code>, even if it were trying to invoke <code>getmsg()</code>.

On the other hand, using <code>synchronized</code> methods can become a bottleneck if your methods perform long-running operations - all threads, even if they want to invoke other methods in that object that could be interleaved, will still have to wait.

IMO, in your simple example, it's ok to use synchronized methods since you actually have two methods that should not be interleaved. However, under different circumstances, it might make more sense to have a lock object to synchronize on, as shown in Joh Skeet's answer.

blocks|key|911649|text|对于此功能，最好根本不使用锁。尝试AtomicReference。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|911650|public+class+Sample+{
++++private+final+AtomicReference<String>+msg+=+new+AtomicReference<String>();

++++public+void+setMsg(String+x)+{
++++++++msg.set(x);
++++}

++++public+String+getMsg()+{
++++++++return+msg.getAndSet(null);
++++}
}|code-block|syntax|javascript|911651|不需要锁，代码更简单。在任何情况下，它都使用一个标准的结构来做你想要的事情。|911652|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|K|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|L|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|M|8|@]|9|@]|A|$]]|$1|I|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|J|$]]

For this functionality you are better off not using a lock at all. Try an AtomicReference.

<pre><code>public class Sample {
 private final AtomicReference&lt;String&gt; msg = new AtomicReference&lt;String&gt;();

 public void setMsg(String x) {
 msg.set(x);
 }

 public String getMsg() {
 return msg.getAndSet(null);
 }
}
</code></pre>

No locks required and the code is simpler IMHO. In any case, it uses a standard construct which does what you want.

blocks|key|695614|text|从Java1.5开始，考虑java.util.concurrent包总是一个好主意。它们是目前java中最先进的锁定机制。synchronize机制比java.util.concurrent类更重要。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|695615|示例如下所示：|695616|import+java.util.concurrent.locks.Lock;
import+java.util.concurrent.locks.ReentrantLock;

public+class+Sample+{

++++private+final+Lock+lock+=+new+ReentrantLock();

++++private+String+message+=+null;

++++public+void+newmsg(String+msg)+{
++++++++lock.lock();
++++++++try+{
++++++++++++message+=+msg;
++++++++}+finally+{
++++++++++++lock.unlock();
++++++++}
++++}

++++public+String+getmsg()+{
++++++++lock.lock();
++++++++try+{
++++++++++++String+temp+=+message;
++++++++++++message+=+null;
++++++++++++return+temp;
++++++++}+finally+{
++++++++++++lock.unlock();
++++++++}
++++}
}|code-block|syntax|javascript|695617|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|$]]

From Java 1.5 it's always a good Idea to consider java.util.concurrent package. They are the state of the art locking mechanism in java right now. The synchronize mechanism is more heavyweight that the java.util.concurrent classes.

The example would look something like this:

<pre><code>import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;

public class Sample {

 private final Lock lock = new ReentrantLock();

 private String message = null;

 public void newmsg(String msg) {
 lock.lock();
 try {
 message = msg;
 } finally {
 lock.unlock();
 }
 }

 public String getmsg() {
 lock.lock();
 try {
 String temp = message;
 message = null;
 return temp;
 } finally {
 lock.unlock();
 }
 }
}
</code></pre>

Let me use this small and simple sample:

<pre><code>class Sample {
 private String msg = null;

 public void newmsg(String x){
 msg = x;
 }

 public String getmsg(){
 String temp = msg;
 msg = null;
 return temp;
 }
}
</code></pre>

Let's assume the function <code>newmsg()</code> is called by other threads that I don't have access to. 

I want to use the synchonize method to guarantee that the string <code>msg</code> is only used by one function per time. In other words, function <code>newmsg()</code> cannot run at the same time as <code>getmsg()</code>.

How to synchronize or lock upon variables in Java?

让我使用这个小而简单的示例：class Sample {    private String msg = null;    public void newmsg(String x){        msg = x;    }    public String getmsg(){        String temp =...

问如何在Java中同步或锁定变量？
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