Java，线程无法启动

Question

I don't understand why this only printing 2 actives threads.

/* worker from the example */
for(int i = 0 ; i < 4 ; ++i){
    Worker worker = new Worker(articles, factory);
    worker.start();
    workers.add(worker);            
}       

System.out.println("Number of active threads : " + Worker.activeCount());

My Worker class is written likes this :

class Worker extends Thread{}

Answer 1

Threads take time to start and execute. The current thread doesn't stop and wait for them to start. This means you might not see any threads start by the time you print that message.

Note: the whole purpose of threads is to run code independently as possible. You can't make assumptions about the order in which things happen unless you have explicitly written code to guarantee this.