How to write a Singleton in proper manner?

Question

Today in my interview one interviewer asked me to write a Singleton class. And i gave my answer as

public class Singleton {

    private static Singleton re         


        

Answer 1

A thread safe version of the OPs initial approach, plus no one else dared to suggest a synchronized statement.

final class Singleton
{
    private static Object lock = new Object();
    private static volatile Singleton instance = null;
    private Singleton() { }
    public static Singleton getInstance()
    {
        if(instance == null)
        {
            synchronized(lock)
            {
                if(instance == null)
                {
                    instance = new Singleton();
                }
            }
        }
        return instance;
    }
}