Synchronization in java with example

In this section we will discuss about Synchronization in java.

Synchronization in java with example

In this section we will discuss about Synchronization in java. Since java is a multi-threaded language so, when two or more thread used a shared resources that lead to two kind of errors: thread interference and memory consistency error, to avoid this error you need to synchronized object,  that the resource will be used by one thread at a time and the process by which synchronization is achieved is called synchronization. Synchronized keyword in java create a critical section in which a lock is associated with the object . To enter the critical section a thread need to obtain the object lock. The general form of synchronized is as follows

synchronized(object)
{
 statement;
}

1. Process Synchronization.
2. Thread Synchronization.

There are two types of thread synchronization Mutual Exclusive and Inter-thread communication. Mutual Exclusion is achieved by making  a method or a block synchronized. Mutual exclusion will keep a thread from interfering with another thread while sharing data. Synchronization is done with a lock on object means every object has a lock and if a thread need to access that object field have to acquire the lock before access them and release the lock when done. A method is synchronized using synchronized keyword.

Example : Understanding the problem without synchronization.

class Demo
{
  public void print(int n)
  {
	  for(int i=1;i<=5;i++)
	  {
		  System.out.println(n*i);
	  try { Thread.sleep(500);
	  
	  }catch(Exception e){System.out.println(e);}
	    
	  }
  }
}
 class Threaddemo extends Thread
 {
	 Demo d;
	 Threaddemo(Demo d)
	 {
		this.d=d;
	 }
   public void run()
   {
	   d.print(5);
   }
 
 } class Threaddemo1 extends Thread
  {
	 Demo d;
	 Threaddemo1(Demo d)
	 {
		this.d=d;
	 }
	 public void run()
	   {
		   d.print(10);
	   }
	 }
  public class Main
  {
	 public static void main(String args[])
	 {
		 Demo d=new Demo();
		 Threaddemo ob1=new Threaddemo (d);
		 Threaddemo1 ob2=new  Threaddemo1(d);
	     ob1.start();
	     ob2.start();
	 }
  }

Output : After Compiling and executing the above program

Understanding  the problem with Synchronization.

class Second
{
  public synchronized void print(int n)
  {
	  for(int i=1;i<=5;i++)
	  {
		  System.out.println(n*i);
	  try { Thread.sleep(500);
	  
	  }catch(Exception e){System.out.println(e);}
	    
	  }
  }
}
 class Third extends Thread
 {
	 Second d;
	 Third(Second d)
	 {
		this.d=d;
	 }
   public void run()
   {
	   d.print(5);
   }
 
 }
 
 
 class Fourth extends Thread
 {
	 Second d;
	 Fourth(Second d)
	 {
		this.d=d;
	 }
	 public void run()
	   {
		   d.print(10);
	   }
	 }
  public class Main2
  {
	 public static void main(String args[])
	 {
		 Second d=new Second();
		 Third ob1=new Third (d);
		 Fourth ob2=new  Fourth(d);
	     ob1.start();
	     ob2.start();
	 }
  }

Output :  After compiling and executing the above program.