Thread safety for static variables

Question

class ABC implements Runnable {
    private static int a;
    private static int b;
    public void run() {
    }
}

I have a Java class as above. I hav

Answer 1

Use a synchronized method, e.g.

public synchronized void increment()
{
  a++; b++;
  // push in to hash table.
}

The above is good if you are accessing the statics through a single instance, however if you have multiple instances, then you need to synchronize on some static object - something like (untested)..

private static Object lock = new Object();

in the method

public void increment()
{
  synchronize(lock)
  {
    a++;b++;
    // do stuff
  }
}

NOTE: These approaches assume that you want to increment a and b in one atomic action, the other answers highlight how they can be individually incremented using atomics.