Difference between synchronized method and synchrozed block

[Anwar Hussain]

Hi,

Can some body explain the difference between synchronized method and synchrozed block.

Thanks

[Patricia Samuel]

See it here

[Anwar Hussain]

Patricia Samuel wrote:See it here

Its confusing me

[Patricia Samuel]

with a synchronized block you can choose what to synchronize on. With a synchronized method, an instance method always synchronizes on the instance, a static method always synchronizes on the class.

public synchronized void methodName() {  
    // ...code here  
}  
   
 public void methodName() {  
     synchronized (this) {  
         // ...code here  
     }  
 }     

synchronized(this) can have any object you want to synchronize where as when a method is synchronized it will work with instance for which it is called.

[Anwar Hussain]

Patricia Samuel wrote:with a synchronized block you can choose what to synchronize on. With a synchronized method, an instance method always synchronizes on the instance, a static method always synchronizes on the class.

public synchronized void methodName() {  
    // ...code here  
}  
   
 public void methodName() {  
     synchronized (this) {  
         // ...code here  
     }  
 }     

synchronized(this) can have any object you want to synchronize where as when a method is synchronized it will work with instance for which it is called.

So when a thread is in the middle of execution of the synchronized block with 'this' as argument , can another thread call a synchronzed method of that same object???

[Embla Tingeling]

Anwar Hussain wrote:So when a thread is in the middle of execution of the synchronized block with 'this' as argument , can another thread call a synchronzed method of that same object???

It doesn't matter whether a whole method is synchronized or just a block. Synchronized always means the synchronized code section can be run by one thread at a time only.

[Vivek Singh]

Anwar Hussain wrote:So when a thread is in the middle of execution of the synchronized block with 'this' as argument , can another thread call a synchronzed method of that same object???

 public synchronized void doStuff () {
    System.out.println("synchronized");
}
   

Is equivalent to :-

public void doStuff() {
    synchronized(this) {
        System.out.println("synchronized");
    }
}
    

Form K&B
"When you synchronize a method, the object used to invoke the method is the object whose lock must be acquired. But when you synchronize a block of code, you specify which object's lock you want to use as the lock, so you could, for example, use some third-party object as the lock for this piece of code. That gives you the ability to have more than one lock for code synchronization within a single object."