Synchronized Block in Java

Synchronized block can be used to perform synchronization on any specific resource of the method.

Suppose you have 50 lines of code in your method, but you want to synchronize only 5 lines, you can use synchronized block.

If you put all the codes of the method in the synchronized block, it will work same as the synchronized method.

Points to remember

Synchronized block is used to lock an object for any shared resource.
Scope of synchronized block is smaller than the method.

Syntax

synchronized (object reference expression) { 
   //code block 
 }

Example

Let's see the simple example of synchronized block.

Program of synchronized block

snippet

class Table{

 void printTable(int n){
   synchronized(this){//synchronized block
     for(int i=1;i<=5;i++){
      System.out.println(n*i);
      try{
       Thread.sleep(400);
      }catch(Exception e){System.out.println(e);}
     }
   }
 }//end of the method
}

class MyThread1 extends Thread{
Table t;
MyThread1(Table t){
this.t=t;
}
public void run(){
t.printTable(5);
}

}
class MyThread2 extends Thread{
Table t;
MyThread2(Table t){
this.t=t;
}
public void run(){
t.printTable(100);
}
}

public class TestSynchronizedBlock1{
public static void main(String args[]){
Table obj = new Table();//only one object
MyThread1 t1=new MyThread1(obj);
MyThread2 t2=new MyThread2(obj);
t1.start();
t2.start();
}
}

Output

Output:5 10 15 20 25 100 200 300 400 500

Synchronized block by using anonymous class

Same Example of synchronized block by using anonymous class:

//Program of synchronized block by using anonymous class

snippet

class Table{

void printTable(int n){
   synchronized(this){//synchronized block
     for(int i=1;i<=5;i++){
      System.out.println(n*i);
      try{
       Thread.sleep(400);
      }catch(Exception e){System.out.println(e);}
     }
   }
}//end of the method
}

public class TestSynchronizedBlock2{
public static void main(String args[]){
final Table obj = new Table();//only one object

Thread t1=new Thread(){
public void run(){
obj.printTable(5);
}
};
Thread t2=new Thread(){
public void run(){
obj.printTable(100);
}
};

t1.start();
t2.start();
}
}

Output

Output:5 10 15 20 25 100 200 300 400 500