JAva readにもロックが必要です

今日readに鍵をかける必要があるかと聞かれ、答えられませんでした.自分でプログラムを書いてみましたが、答えは肯定的で、readロックは実行の順序を保証し、スレッドが汚れたデータを読まないようにするためです.

public class TestThread {
	private int a = 1;

	public synchronized void add(){
		this.a = this.a + 1;
		System.out.println(Thread.currentThread().getName() + "current a is " + a);
	}

	public int get(){
		System.out.println("current a is " + a);
		return a;
	}

	public static void main(String[] args) throws Exception{
		final TestThread testThread = new TestThread();
		Thread t1 = new Thread(new Runnable(){
			public void run(){
				testThread.add();
				//make sure the second thread to be executed at this moment
				try {
					Thread.sleep(10000);
				} catch (InterruptedException e) {
					// TODO Auto-generated catch block
					e.printStackTrace();
				}

				testThread.get();
			}
		}
		);

		Thread t2 = new Thread(new Runnable(){
			public void run(){
				//make sure the first thread to be started firstly at beginning
				try {
					Thread.sleep(5000);
				} catch (InterruptedException e) {
					// TODO Auto-generated catch block
					e.printStackTrace();
				}
				testThread.add();
				testThread.get();
			}
		}
		);

		t1.start();
		t2.start();
	}
}

output:
Thread-0current a is 2
Thread-1current a is 3
current a is 3
current a is 3
testThread.add();testThread.get();ロックをかけると、さっき汚れたデータを読んだ問題は発生しません.