Access static variable in synchronized block

问题:

(Java synchronization problem)As my title, can I access a static variable in a synchronized block? Will it cause inconsistency ? Can anyone tell me the detail of the disadvantages or advantages of accessing a static variable synchronized block.

回答1:

can I access a static variable in a synchronized block ?

Yes, You can.

Will it cause inconsistency ?

Static means shared across all the instances of that Class in a JVM. Shared resources are not thread-safe.Hence Static variables are not thread safe.So, if multiple threads tries to access a static variable, it may result in inconsistency.

The ways, which I know of to synchronize access to a static variable.

1. Synchronize on Static object.

      public class SomeClass{
         private static int sum = 0;
         private static final Object locker = new Object();
   
         public void increaseSum() {
              synchronized (locker) {
              sum++;
         }
       }
     }
   

2. Synchronized Static method.

   public class SomeClass {
       private static int sum = 0;
   
      public static synchronized void increaseSum() {
        sum++;
    }
   }
   

3. Synchronize on class object

    public class SomeClass {
       private static int sum= 0;
   
       public void increaseSum() {
          synchronized (SomeClass .class) {
          sum++;
        }
      }
    }