Static Synchronized Method Behavior

Question

What does the use of the 'static synchronized' keyword in the increment() method ensure in this example?
 
```java
public class StaticInstanceSync {
    private static int counter = 0;
    
    public static synchronized void increment() {
        counter++;
    }
    
    public void runTask() {
        for(int i = 0; i < 1000; i++) {
            increment();
        }
    }
    
    public static void main(String[] args) throws InterruptedException {
        StaticInstanceSync sis1 = new StaticInstanceSync();
        StaticInstanceSync sis2 = new StaticInstanceSync();
        Thread t1 = new Thread(() -> sis1.runTask());
        Thread t2 = new Thread(() -> sis2.runTask());
        t1.start();
        t2.start();
        t1.join();
        t2.join();
        System.out.println(counter);
    }
}
```

Accepted Answer

It ensures that only one thread, across all instances, executes the increment() method at a time, preventing race conditions on the counter variable.

Answer

It guarantees atomic updates to the counter variable without any performance cost.

Answer

It mistakenly synchronizes on the instance lock, rendering the static method non-thread-safe.

Answer

It only synchronizes threads accessing the same instance, so race conditions may occur between different instances.

Question Leaderboard