My arduino sends "1" on serial at each pulse. I want to count the number of pulses on Processing. Sometimes the number is incremented twice, what can I do ?

My code :

2.   // if Arduino sent something on the console, increment the 2 counters
3.   if(myPort.available() > 0)
4.   {
5.     myPort.clear();
6.     counter++;
7.     counterByHour++;
8.     println(counter);
9.     
10.     // Arduino sends "on", so there are more caractere,
11.     // this clear the variable
12.     myPort.clear();
13.   }

Thanks :)