Is a static counter thread safe in multithreaded application?

Question

public class counting
{
  private static int counter = 0;

  public void boolean counterCheck(){
  counter++;
  if(counter==10)
  counter=0;
  }
}

Answer 1

first of counter++ by itself is NOT threadsafe

hardware limitations make it equivalent to

int tmp = counter;
tmp=tmp+1;
counter=tmp;

and what happens when 2 threads are there at the same time? one update is lost that's what

you can make this thread safe with a atomicInteger and a CAS loop

private static AtomicInteger counter = new AtomicInteger(0);

public static boolean counterCheck(){
    do{
        int old = counter.get();
        int tmp = old+1;
        if(tmp==10)
            tmp=0;
        }
    }while(!counter.compareAndSet(old,tmp));
}