在我的示例中，同步和锁定有什么区别?

Task class includes a method named doSomething() to print the thread name and executing elapsed time.

import java.util.Calendar;

public class Task {
    public void doSomething() {
        try {
            Thread.sleep(2000);
        } catch (InterruptedException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }

        StringBuilder sb = new StringBuilder();
        //Thread Name
        sb.append("Thread Name: ").append(Thread.currentThread().getName());

        //Timestamp  for the executing
        sb.append(", elaspsed time: ").append(Calendar.getInstance().get(13)).append(" s ");
        System.out.println(sb.toString());
    }
}

TaskWithLock 类

import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;

public class TaskWithLock extends Task implements Runnable {
    private final Lock lock = new ReentrantLock();

    @Override
    public void run() {
        try {
            lock.lock();
            doSomething();
        } finally {
            lock.unlock();
        }

    }
}

TaskWithSync 类

public class TaskWithSync extends Task implements Runnable {

    @Override
    public void run() {
        synchronized ("A") {
            doSomething();
        }
    }
}

主类

public class Main {
    public static void runableTasks(Class<? extends Runnable> clz)
            throws Exception {
        ExecutorService service = Executors.newCachedThreadPool();

        System.out.printf("<-- Start executing %s Task --> 
",
                clz.getSimpleName());

        // Start 3 threads
        for (int i = 0; i < 3; i++) {
            service.submit(clz.newInstance());
        }

        // Wait for some time, and then close the executor
        TimeUnit.SECONDS.sleep(10);
        System.out
                .printf("<-- %s Tasks is complet --> 
", clz.getSimpleName());
        service.shutdown();
    }

    public static void main(String[] args) throws Exception {
        //Execute tasks with Lock
        runableTasks(TaskWithLock.class);

        //Execute tasks with Synchronized 
        //runableTasks(TaskWithSync.class);
    }
}

第一次，通过调用runableTasks(TaskWithSync.class)方法同步执行任务；

<-- Start executing TaskWithSync Task --> 
Thread Name: pool-1-thread-1, elaspsed time: 28 s 
Thread Name: pool-1-thread-3, elaspsed time: 30 s 
Thread Name: pool-1-thread-2, elaspsed time: 32 s 
<-- TaskWithSync Tasks is complet --> 

第二次，调用方法runableTasks(TaskWithLock.class);

<-- Start executing TaskWithLock Task --> 
Thread Name: pool-1-thread-3, elaspsed time: 23 s 
Thread Name: pool-1-thread-2, elaspsed time: 23 s 
Thread Name: pool-1-thread-1, elaspsed time: 23 s 
<-- TaskWithLock Tasks is complet --> 

上面的例子使用 Lock 和 synchronized 来运行任务，我这里有一些问题:

private final Object lock = new Object();

public void run() {
    synchronized (lock) {
        doSomething();
    }
}