In most places, this is the implementation followed for Singleton Design Pattern.

It makes use of the keyword volatile to prevent the issue of partial object creation (establishes happens-before relation between reads and writes to instance).

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

I was wondering if we could avoid the usage of volatile by making the entire getInstance() method synchronized? If it does not work, how would the execution of both cases differ?