Threads Syncronization in java

class SynchronizeDemo2
{
    public static void main(String args[])
    {
        Shared shared = new Shared();
        CustomThread thread1 = new CustomThread(shared, "one");
        CustomThread thread2 = new CustomThread(shared, "two");
        CustomThread thread3 = new CustomThread(shared, "three");
        CustomThread thread4 = new CustomThread(shared, "four");
        try
        {
            thread1.join();
            thread2.join();
            thread3.join();
            thread4.join();
        }
        catch(InterruptedException e) {}
    }
}

class CustomThread extends Thread
{
    Shared shared;
    public CustomThread(Shared shared, String string)
    {
        super(string);
        this.shared = shared;
        start();
    }
    public void run()
    {
        shared.doWork(Thread.currentThread().getName());
    }
}

class Shared
{
     synchronized void doWork(String string)
    {
        System.out.println("Starting " + string);
        try
        {
            Thread.sleep(1000);
        }
        catch (InterruptedException e) {}
        System.out.println("Ending " + string);
    }
}