在同步块中访问静态变量

Question

(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.

Answer 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++; } } }