设计模式之单例模式

经过多方博客，文章参考，枚举是实现单例模式的最好方式

public enum Singleton {
     INSTANCE;
     public void businessMethod() {
          System.out.println("我是一个单例！");
     }
}

public class MainClass {
    public static void main(String[] args) {
        Singleton s1 = Singleton.INSTANCE;
        Singleton s2 = Singleton.INSTANCE;
        System.out.println(s1==s2);
    }
}
将一个已有的类改造为单例类

public class Singleton {
    private Singleton(){
    }
    public static enum SingletonEnum {
        SINGLETON;
        private Singleton instance = null;
        private SingletonEnum(){
            instance = new Singleton();
        }
        public Singleton getInstance(){
            return instance;
        }
    }
}

……
    public static void main(String args[]) {
        Singleton s1 = SingletonEnum.SINGLETON.getInstance();
        Singleton s2 = SingletonEnum.SINGLETON.getInstance();
        System.out.println(s1==s2);
    }
    ……