面试手写题

• 手写单例模式

public class Singleton {
    private Singleton() {
    }

    private enum SingletonHolder {
        HOLDER;
        private Singleton singleton;

        SingletonHolder() {
            singleton = new Singleton();
        }
    }
    
    public static Singleton getInstance() {
        return SingletonHolder.HOLDER.singleton;
    }

}