A \l;class\u cbot\class; method can be declared \c;synchronized\n;. This is to make sure that the method is never being executed by more than one bot at the same time.
Both of them will execute \c;val=nb\n; and wait 2 seconds so both of them will have \c;val=33\n;. With \c;synchronized\n; the first bot starts execution with \c;val=33\n; and then waits 2 seconds and returns. Only once the first bot has returned from the \c;inc\n; method, the second bot will be allowed to enter the \c;inc\n; method and therefore the second bot will always have \c;val=34\n;.
You can have more than one synchronized method in your \l;class\u cbot\class; in order to prevent simultaneous execution across more than one method. In other words: as long as a bot's program is inside a synchronized method, no other bot can enter any synchronized method of the same class.
