Java:如果同步发生变化,它不会阻塞

相关的 Java will synchronized block if changed?

 public class TestConcurrentTwo {
     public static void main(String[] args) {

         class lock {
             public Object lockObj = new Object();
             int protectedValue = 0;
         }
         lock a = new lock();

         Thread t = new Thread(() -> {
             try {
                 synchronized (a.lockObj) {
                     System.out.println("from first block start");
                     System.out.println(a.protectedValue);
                     a.lockObj = new Object();
                     Thread.sleep(1000);
                     System.out.println(a.protectedValue);
                     System.out.println("from first block done");
                 }
             } catch (InterruptedException x) {}
         });
         t.start();
         try {
             Thread.sleep(100);
         } catch (InterruptedException x) {}

         synchronized (a.lockObj) {
             System.out.println("from second block start");
             a.protectedValue++;
             System.out.println("from second block done");
         }

         System.out.println(a.protectedValue);
     }
 }

输出:

from first block start
0
from second block start
from second block done
1
1
from first block done

在相关的答案中,它们都持有原始的引用,因此第二个块应该被阻塞,直到第一个块完成为止。

然而,第二个街区确实进行了一次 a.lockObj 从第一个街区变了。为什么?