singleton pattern

singleton.java

public class Singleton {

    private static Object    obj      = new Object();
    private static Singleton instance = null;

    private Singleton(){
    }

    public static Singleton getInstance() {
        // if already inited, no need to get lock everytime
        if (instance == null) {
            synchronized (obj) {
                if (instance == null) {
                    instance = new Singleton();
                }
            }
        }

        return instance;
    }
}