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POWhat is the correct way to synchronize a shared, static object in Java?
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copied!<p>This is a question concerning what is the proper way to synchronize a shared object in java. One caveat is that the object that I want to share must be accessed from static methods. My question is, If I synchronize on a static field, does that lock the class the field belongs to similar to the way a synchronized static method would? Or, will this only lock the field itself?</p> <p>In my specific example I am asking: Will calling PayloadService.getPayload() or PayloadService.setPayload() lock PayloadService.payload? Or will it lock the entire PayloadService class?</p> <pre><code>public class PayloadService extends Service { private static PayloadDTO payload = new PayloadDTO(); public static void setPayload(PayloadDTO payload){ synchronized(PayloadService.payload){ PayloadService.payload = payload; } } public static PayloadDTO getPayload() { synchronized(PayloadService.payload){ return PayloadService.payload ; } } ... </code></pre> <p>Is this a correct/acceptable approach ? </p> <p>In my example the PayloadService is a separate thread, updating the payload object at regular intervals - other threads need to call PayloadService.getPayload() at random intervals to get the latest data and I need to make sure that they don't lock the PayloadService from carrying out its timer task</p> <p>Based on the responses, I refactored to the following:</p> <pre><code>public class PayloadHolder { private static PayloadHolder holder; private static PayloadDTO payload; private PayloadHolder(){ } public static synchronized PayloadHolder getInstance(){ if(holder == null){ holder = new PayloadHolder(); } return holder; } public static synchronized void initPayload(){ PayloadHolder.payload = new PayloadDTO(); } public static synchronized PayloadDTO getPayload() { return payload; } public static synchronized void setPayload(PayloadDTO p) { PayloadHolder.payload = p; } } public class PayloadService extends Service { private static PayloadHolder payloadHolder = PayloadHolder.getInstance(); public static void initPayload(){ PayloadHolder.initPayload(); } public static void setPayload(PayloadDTO payload){ PayloadHolder.setPayload(payload); } public static PayloadDTO getPayload() { return PayloadHolder.getPayload(); } ... </code></pre> <p>Is this approach legitimate? I am also curious if it is better to do it this way or using the AtomicReference approach mentioned by Hardcoded ...? - I am keeping an instance of PayloadHolder on PayloadService simply to keep a reference to the PayloadHolder class active in the jvm for as long as the PayloadService is running.</p>

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