How synchronized block achieve synchronization

Question

In Java if a method is qualified by synchronized keyword, it ensures that this method will be accessed by a single thread at any time, by manipulating objects monitor such that when a thread enters a synchronized method it locks monitor, so that all other threads know it is already locked by another thread.

My Question here is how does synchronized block achieve synchronization, What I mean is that there is no monitor associated with this synchronized block so what indication it uses to determine if this block is already in execution? I am lost here.

Answer 1

Each object has an implicit lock associated with it. When entering a synchronized block, the process must acquire the object's lock before continuing. The lock is returned upon exiting the synchronized block.

public class SomeClass {
   private Object mutex = new Object();
   public static synchronized void method1() {
      // static methods aquire the class level lock for SomeClass 
   }
   public synchronized void method2() {
      // aquire the lock associated with 'this' instance (of SomeClass)
   }
   public void method3() {
      synchronized (mutex) {
         // aquire the lock of the mutex object
      }
   }
}