threadsafe singleton pattern in java

1package com.journaldev.designpatterns;
2
3public class ASingleton {
4
5	private static volatile ASingleton instance;
6	private static Object mutex = new Object();
7
8	private ASingleton() {
9	}
10
11	public static ASingleton getInstance() {
12		ASingleton result = instance;
13		if (result == null) {
14			synchronized (mutex) {
15				result = instance;
16				if (result == null)
17					instance = result = new ASingleton();
18			}
19		}
20		return result;
21	}
22
23}
24