multithreading - Java Synchronisation with and without static variable -

i have been studying synchronization in java , tried run following program

    public class example {         public static void main(string[] args) {             counter countera = new counter();             counter counterb = new counter();               thread  threada = new counterthread(countera);               thread  threadb = new counterthread(counterb);                threada.start();               threadb.start();          }     }      class counterthread extends thread {         protected counter counter = null;          public counterthread(counter counter){            this.counter = counter;         }         public void run() {         for(int i=0; i<2; i++){               counter.add(i);            }         }     }      class counter {          long count = 0;          public synchronized void add(long value){           this.count += value;           system.out.println(this.count);         }     } 

when run above code , gives me same output when run example class java application or when debug example class

 0  1  0  1 

but if modify access modifier of count variable of counter class static mentioned below :

    static long count = 0; 

and if try run example class output

 0  1  0  2 

but when debug example class output

 0  1  1  2 

can me understand difference. in advance , apologies because new multithreading concepts

each instance has own copy of instance variable(s) share static variable. have 2 instances of class , 2 threads operating on these instances:

        counter countera = new counter();         counter counterb = new counter();         thread  threada = new counterthread(countera);         thread  threadb = new counterthread(counterb); 

so effect clear. when count non-static, 2 threads not affect count of 2 different objects. when count static, 2 threads work on same variable shared 2 instances.

when have 2 independent threads in action, execution order dynamic depending on how thread scheduler picks thread execute. using debugger not affect , infact may see different result normal execution of program.