Creating threads

Definition

A thread is one path of execution. You create one by giving a Thread some code to run (a Runnable, usually a lambda) and calling start(). Call join() to wait until it has finished.

Example code

Three threads each compute a result, and main waits for them

class Demo {
    public static void main(String[] args) throws InterruptedException {
        int[] results = new int[3];
        Thread[] threads = new Thread[3];

        for (int i = 0; i < threads.length; i++) {
            int id = i;
            threads[i] = new Thread(() -> results[id] = (id + 1) * 100, "worker-" + i);   // the code to run
            threads[i].start();                                                             // run it in parallel
        }

        for (Thread thread : threads) thread.join();                                       // wait for all of them

        System.out.println(java.util.Arrays.toString(results));
    }
}

// Output:
// [100, 200, 300]