Synchronized non static method in java What Yasser Ibrahim @Jobilize

Author: Yasser Ibrahim

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Question 220 / 297: What is the possible result of compiling and running the following code?

public class Test implements Runnable {
	Integer id = 0;

	public static void main(String[] args) {
		new Thread(new Test()).start();
		new Thread(new Test()).start();
	}

	public void run() {
		press(id);
	}

	synchronized void press(Integer id) {
		System.out.print(id.intValue());
		System.out.print((++id).intValue());
	}
}

A 1010

B 0101

C 0123

D compilation error

E an exception is thrown at run time

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Explanation:

The two threads are executing on two different instances of Test, which means that the two threads are working on two different instances of variable id.

The result "0123" is not possible, because each thread will start with value "0" for "id"

The result "1010" is not possible because "id" starts with value "0" then incremented to "1"

"0101" is a possible output, which happens the first thread to execute seizes the CPU till it finishes method press()

Another scenario may happen when the the CPU switches between the two threads allowing each to execute one print statement at a time, this will result in the output "0011"

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