java - What is the difference between Thread.join and Synchronised? -

i confused when use thread.join() , when use synchronization in multi threading application.

according me, both of them block or wait execution done other thread.
example has output 10 a's , 10 b's & 10 c's in sequential pattern 1 after other :

1  : 2  : 3  : 4  : 5  : 6  : 7  : 8  : 9  : 10 : 1  : b 2  : b 3  : b 4  : b 5  : b 6  : b 7  : b 8  : b 9  : b 10 : b 1  : c 2  : c 3  : c 4  : c 5  : c 6  : c 7  : c 8  : c 9  : c 10 : c ----program ends---- 

example starts here

class synctest extends thread  {        stringbuffer sb;      public synctest(stringbuffer sb)      {         this.sb = sb;        }      public void run()     {         synchronized(sb)          {             for(int i=1;i<=10;i++){                 system.out.println(i+" : "+sb.charat(0));             }             sb.setcharat(0, (char) (sb.charat(0)+1));         }     }      public static void main(string [] args) throws interruptedexception     {         stringbuffer sb = new stringbuffer("a");         thread t1=new synctest(sb);         thread t2=new synctest(sb);         thread t3=new synctest(sb);          t1.start();          t2.start();          t3.start();          thread.sleep(1000);          system.out.println("----program ends----");     } } 

here, output turns out 10 a's followed 10 b's followed 10 c's in sequential order. can use thread.join instead of synchronized block same output this:

public void run()     {         //removed synchronized statement...              for(int i=1;i<=10;i++){                 system.out.println(i+" : "+sb.charat(0));             }             sb.setcharat(0, (char) (sb.charat(0)+1));      }      public static void main(string [] args) throws interruptedexception     {         stringbuffer sb = new stringbuffer("a");         thread t1=new synctest(sb);         thread t2=new synctest(sb);         thread t3=new synctest(sb);          t1.start();         t1.join();         t2.start(); // wait t1 complete         t2.join();         t3.start(); // wait t2 complete         t3.join();                        // wait t3 complete         system.out.println("----program ends----");     } 

can clear confusion on usage of these 2 techniques i.e. when use thread.join , when use synchronization in multi-threading on java.

thread.join() waits thread finish, whereas synchronized block can used prevent 2 threads executing same piece of code @ same time.

it's hard advise when use 1 on other in general, since serve different purposes. it's rare find example, such code, difference between 2 minimal.

that being said, in first example there no guarantee output alphabetical. can't sure thread synchronized block first. in particular case, join() appropriate.