IoDH 实现的单例模式

public class Singleton {

    private Singleton(){
        System.out.println(Singleton.class);
    }
    
    private static class HolderClass{
        private final static Singleton s = new Singleton();
    }
    
    public static Singleton getInstance(){
        return HolderClass.s;
    }
    
    
    public static void main(String[] args) {
        Singleton s = Singleton.getInstance();
    }
    
}