Java thread practice

App.java

import java.util.concurrent.CountDownLatch;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

public class App {
    private static final int COUNT = 10;
    public static void main( String[] args ) throws InterruptedException {
        // 10回カウントするCountDownLatchを生成
        CountDownLatch countDownLatch = new CountDownLatch(COUNT);
        // Threadを3つ生成するExecutorServiceを生成
        ExecutorService exec = Executors.newFixedThreadPool(3);
        for (int i = 0; i < COUNT; i++) {
            exec.submit(new TestRunnable(countDownLatch));
        }
        // 各TestRunnableオブジェクトに渡したcountDownLatchオブジェクト
        // のカウントダウンがすべて修了するまで待ち受け。
        countDownLatch.await();
        System.out.println("finished!");
    }
}

TestRunnable.java

import java.util.concurrent.CountDownLatch;

public class TestRunnable implements Runnable {
    private final CountDownLatch countDownLatch;
    TestRunnable(CountDownLatch countDownLatch) {
        this.countDownLatch = countDownLatch;
    }
    public void run() {
        // 処理を実行してから受け取ったCountDownLatchをカウントアップ
        System.out.println(Thread.currentThread().getId());
        countDownLatch.countDown();
    }
}