Examlab Thread question

[Anu Bhagat]

Hi,

I am having difficulty understandinng this code.
doSleep() method is a static method. why it is possible to call it from run ( non static method.)
Please explain. Thanks.

Anu

    
class A implements Runnable{
     public static void doSleep(int y){
          try{
               Thread.sleep(y);
          }catch(Throwable e){
          }
     }
     public synchronized void run(){
          doSleep(500);
          System.out.println(Thread.currentThread().getName());
          doSleep(500);
     }
}
public class Multi{
     public static void main(String arguments[]){
          Thread rba=new Thread(new Thread(new A()));
          Thread rbb=new Thread(new Thread(new A()));
          rba.start();
          rbb.start();
     }
}

[Jisha Anand]

Anu Bhagat wrote:Hi,
doSleep() method is a static method. why it is possible to call it from run ( non static method.)

Hi Anu,

Why is it impossible? We can always call static method from non-static context right? But the other way around - calling non-static from static context is not possible!

I think you got confused with static modifier; understand that static members are class properties which are loaded by the JVM when the class is loaded; but instance members are loaded only when an instance is created. So by the time an instance is instantiated, its static members would be in place right? So no problem calling them by static members right?

Hope you are not more confused now

[Ninad Kulkarni]

Hi, Anu

One class member is shared among all instances of class.
If class method want to call instance method then class member need to know object reference to call instance method of particular object. Without object reference class method doesn't know which instance method to call.

[Anu Bhagat]

Thanks. I got mixed up and couldn't see it clearly. ok now
Anu

[Fritz Guerilus]

Hi,
I have a follow up question:
How can the doSleep() method pass an int argument, to the sleep() method which takes a long?
-Thank you

[Ankit Garg]

There will be automatic upcast from int to long...

[Fritz Guerilus]

Ankit Garg wrote:There will be automatic upcast from int to long...

Ok, so if it were the other around, a long being sent to a int, it would require a explicit downcast, or else it would fail.
Is that correct?
-Thank you

[Guillaume Jeudy]

If it's a long sent to an int it requires an explicit downcast otherwise it won't compile.

except when the long is a literal or constant whose value fit inside an int. In such a case the long value is implicit narrowed to an int with
no explicit casting required.

[Ankit Garg]

Guillaume Jeudy wrote:except when the long is a literal or constant whose value fit inside an int. In such a case the long value is implicit narrowed to an int with
no explicit casting required.

This is not true. An implicit type cast from long to int is never performed

int i = 2L;       //error
final long l = 23L;
i = l;            //error

An implicit down cast is performed from int (literal or compile time constant) to short or byte (in range of course) but that too doesn't apply to method calls...