Several thread-safe singleton collection

1. static inner class

 

public class Singleton {

    // Private constructor prevents instantiation from other classes
    private Singleton() {
    }

    /**
     * SingletonHolder is loaded on the first execution of
     * Singleton.getInstance() or the first access to SingletonHolder.INSTANCE,
     * not before.
     */
    private static class SingletonHolder {
        public static final Singleton INSTANCE = new Singleton();
    }

    public static Singleton getInstance() {
        return SingletonHolder.INSTANCE;
    }
    
}

 

2. to be continued