By using wait(),notify and notifyall() methods in the code.

Threads are synchronized in two ways.

1) block level
2) Method level

Block level synhronization is the better performance 
compare to method level.

Block Level: 
see the code syntax for block level
synchronized {..
....//code to lock the specific object here..
...}

Method Level:
 See the syntax
   public void synchronized XXXMethodName(Parameters or 
object to acquire locking){.....
...}