Kann mir jemand erklären, warum diese Codes nicht die gleichen Ergebnisse liefern (der einzige Unterschied zwischen zwei Codes liegt in der run () -Methode)?

NB: Der erste Code scheint keine Sperre zu machen!

Erster Code:

class LetterThread extends Thread 
{

    private StringBuffer letter;

    public static void main(String[] args) {
        StringBuffer sbltr = new StringBuffer("A");

        LetterThread one = new LetterThread(sbltr);
        LetterThread two = new LetterThread(sbltr);
        LetterThread three = new LetterThread(sbltr);

        one.setName("Thread ONE");
        two.setName("Thread TWO");
        three.setName("Thread THREE");

        one.start();
        two.start();
        three.start();

    }

    LetterThread(StringBuffer letter) {
        this.letter = letter;
    }

    public synchronized void run() {
        {
            for (int x = 0; x < 100; x++) {
                System.out.println(Thread.currentThread().getName() + " (" + x
                        + ") = " + letter);
            }

            letter.setCharAt(0, (char) (letter.charAt(0) + 1));
        }
    }
}

Zweiter Code: Dieser Code funktioniert genau wie erwartet zu

class LetterThread extends Thread 
{

    private StringBuffer letter;

    public static void main(String[] args) {
        StringBuffer sbltr = new StringBuffer("A");

        LetterThread one = new LetterThread(sbltr);
        LetterThread two = new LetterThread(sbltr);
        LetterThread three = new LetterThread(sbltr);

        one.setName("Thread ONE");
        two.setName("Thread TWO");
        three.setName("Thread THREE");

        one.start();
        two.start();
        three.start();

    }

    LetterThread(StringBuffer letter) {
        this.letter = letter;
    }

    public void run() {
        synchronized (letter) {
            for (int x = 0; x < 100; x++) {
                System.out.println(Thread.currentThread().getName() + " (" + x
                        + ") = " + letter);
            }

            letter.setCharAt(0, (char) (letter.charAt(0) + 1));
        }
    }