java multithreading wait for all threads to die

i have a problem, i create an aribrary number of threads in a for loop wich i want to run cuncurrently, but i need to wait for all of them to be finished executing before i can continue... anyone know if this is possible??

			Sum thesum = new Sum(N);
			for(int i=0; i<N; i++){
				childProcess thread = new childProcess(N, i, darray[i], thesum);
				thread.start();
			}
                        //WHAT CAN I PUT HERE?
			thesum.print();

you could set up something with Object.wait() and Object.notify()... make a flag object, make the main thread wait on it. and have the other threads call notify when they're done.