What is the point of making the singleton instance volatile while using double lock? [duplicate]

Answer 1

Write to a volatile field will happen before any read operation. Below is an example code for better understanding:

private static volatile ResourceService resourceInstance;
//lazy Initialiaztion
public static ResourceService getInstance () {
    if (resourceInstance == null) { // first check
        synchronized(ResourceService.class) {
            if (resourceInstance == null) { // double check
                // creating instance of ResourceService for only one time
                resourceInstance = new ResourceService ();                    
            }
        }
    }
    return resourceInstance;
}

This link can serve you better http://javarevisited.blogspot.com/2011/06/volatile-keyword-java-example-tutorial.html