Initializing two threads with the same instance of a runnable

Question

Is it bad programming to initialize two threads with the same instance of a runnable? What difference would it make to initialize with separate instances of a runnable, and

Answer 1

To make understand easily(based on the comment of Stephen), added the below program block about the impact of accessing the instance variable from a non-synchronized block with the same instance of Runnable displays the unexpected results.

public class SynchronizedInstanceMethod implements Runnable{

private int counter;

public SynchronizedInstanceMethod(int counterValue){
    this.counter = counterValue;
}

private synchronized void displayMessage(){
    System.out.println(" Display Message ");
}

private void modifyCounter(){
    this.counter++;
    System.out.println("Value -- "+ this.counter);
}

@Override
public void run() {
    this.displayMessage();
    this.modifyCounter();
}

public static void main(String[] args) {
    SynchronizedInstanceMethod instance = new SynchronizedInstanceMethod(5);
    new Thread(instance).start();
    new Thread(instance).start();
}
}