Can a thread call a non-synchronized instance method of an Object when a synchronized method is being executed

Yes, a Non synchronized method can always be called without any problem. In fact Java does not do any check for a non-synchronized method. The Lock object check is performed only for synchronized methods/blocks. In case the method is not declared synchronized Jave will call even if you are playing with shared data. So you have to be careful while doing such thing. The decision of declaring a method as synchronized has to be based on critical section access. If your method does not access a critical section (shared resource or data structure) it need not be declared synchronized. Below is the example which demonstrates this, The Common class has two methods synchronizedMethod1() and method1() MyThread class is calling both the methods in separate threads,

public class Common {

public synchronized void synchronizedMethod1() {

System.out.println(“synchronizedMethod1 called”);

try {

Thread.sleep(1000);

} catch (InterruptedException e) {

e.printStackTrace();

}

System.out.println(“synchronizedMethod1 done”);

}

public void method1() {

System.out.println(“Method 1 called”);

try {

Thread.sleep(1000);

} catch (InterruptedException e) {

e.printStackTrace();

}

System.out.println(“Method 1 done”);

}

}

public class MyThread extends Thread {

private int id = 0;

private Common common;

public MyThread(String name, int no, Common object) {

super(name);

common = object;

id = no;

}

public void run() {

System.out.println(“Running Thread” + this.getName());

try {

if (id == 0) {

common.synchronizedMethod1();

} else {

common.method1();

}

} catch (Exception e) {

e.printStackTrace();

}

}

public static void main(String[] args) {

Common c = new Common();

MyThread t1 = new MyThread(“MyThread-1”, 0, c);

MyThread t2 = new MyThread(“MyThread-2”, 1, c);

t1.start();

t2.start();

}

}  

Here is the output of the program

Running ThreadMyThread-1

synchronizedMethod1 called

Running ThreadMyThread-2

Method 1 called

synchronizedMethod1 done

Method 1 done

This shows that method1() – is called even though the synchronizedMethod1() was in execution.