java - How threads work -

i have problem understanding how threads work:

class threadtest implements runnable{      synchronized void methoda(long n){          (int i=1;i<3;i++){system.out.print(n+" "+i)}      }       public void run(){          methoda(thread.currentthread.getid());      }       public static void main(string ... args){          new thread(new threadtest()).start();          new thread(new threadtest()).start();      }  }  

as understand, because methoda synchronized loop in method, must finish before next thread calls method -- result must 4-1 4-2 5-1 5-2...

is possible have result 4-1 5-1 5-2 4-2? if yes, how?

is possible have result 4-1 5-1 5-2 4-2.?

it possible.

if yes how?

you using this reference object locked synchronized. since you've got 2 distinct instances of threadtest, each method locks own instance , mutual exclusion not achieved.

so, must understand semantics of synchronized: there defined object involved monitor acquired. basically, object notes thread has acquired monitor , allow same thread re-acquire it; other threads put on hold until monitor released. other object, naturally, has nothing , monitor free acquired thread.

a synchronized method implicitly uses this lock. can example declare static final object lock = new object(); , use synchronized(lock) in method.