What are some things in the class library you wish more people knew about or used?

    
class LongRunningAction implements Runnable {
    private String threadName;
    private Phaser ph;

    LongRunningAction(String threadName, Phaser ph) {
        this.threadName = threadName;
        this.ph = ph;
        ph.register();
    }

    @Override
    public void run() {
        ph.arriveAndAwaitAdvance();
        try {
            Thread.sleep(20);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        ph.arriveAndDeregister();
    }
}

  

    
executorService.submit(new LongRunningAction("thread-1", ph));
executorService.submit(new LongRunningAction("thread-2", ph));
executorService.submit(new LongRunningAction("thread-3", ph));