can I make static method / block as synchronized ? how does it work ?

[Kavita Kale]

Hi,

I am bit confused in static & synchronized .....

can I make static method / block as synchronized ? and how does it work ?
is it works at class level ?

bye ...

[dhwani mathur]

Hi Kavita


As per i know you can make static method as synchronized
i am not sure about static blocks so i cant say on it......

About its behaviour is ,i hope you must be knowing that static methods
are not related to instance of class so they can be called without object,
second thing is as it is synchronized so it can be used only by one thread at a time...........

and you asked how will it work so i can say on this you first try some code than you can bring up more queries............

[Burkhard Hassel]

Howdy Kavita,

yes it works on class level.

All static methods that are marked "synchronized" will block on the class.

E.g.:

class Sync {
static synchronized void method() {
for (int i=0; i<10; i++) {
String s = Thread.currentThread().getName();
System.out.print(s + " ");
try {
Thread.sleep(77);
} catch (InterruptedException ie) {
ie.printStackTrace();
}
}
System.out.println();
}
}
 
class SyncThread implements Runnable{

public void run() {
Sync.method();
}
 
public static void main(String[] args){
Thread one = new Thread(new SyncThread());
one.setName("one");
one.start();
Thread two = new Thread(new SyncThread());
two.setName("two");
two.start();
}
}

produces:
one one one one one one one one one one
two two two two two two two two two two

Because it is synchronized, thread "two" will wait.

When you remove the "synchronized" keyword from method method() it will produce
one two one two one two one two one two one two one two one two one two one two


static blocks (class initializers) cannot and need not be marked synchronized. It is useless, the class will be loaded only once, and there will be no interferences.


But I guess, you meant blocks inside static methods. In this case you must specify the class literal as the object the lock is on.
For the above method you could also write:

class Sync {
static void method() {
// [B]class literal[/B] goes into sync brackets:
synchronized([B]Sync.class[/B]) { 
for (int i=0; i<10; i++) {
String s = Thread.currentThread().getName();
System.out.print(s + " ");
try {
Thread.sleep(77);
} catch (InterruptedException ie) {
ie.printStackTrace();
}
}
System.out.println();
}
}
}
//other class remains the same

This will behave just as if the whole static method is declared synchronized. Of course you could also sync only relative parts of the method, but in this example the whole thing is synchronized.

Dont't forget that Thread.sleep() does not return the lock, so it behaves "neutral".

Hoped that helped.


Yours,
Bu.