茴香豆系列之单例的几种写法

1. 懒汉式

public class Singleton {private static Singleton instance;private Singleton(){}public static synchronized Singleton getInstance(){if (instance == null) {instance = new Singleton();}return instance;}
}

2. 饿汉式

public class Singleton {private static Singleton instance = new Singleton();private Singleton(){}public static Singleton getInstance(){return instance;}
}

3. 静态内部类

public class Singleton {private static class SingletonHolder{private static final Singleton instance = new Singleton();}private Singleton(){}public static final Singleton getInstance(){return SingletonHolder.instance;}
}

4. 枚举式

public enum Singleton {instance;public void somthing(){}
}

5. 锁两遍

public class Singleton {private volatile static Singleton singleton;private Singleton(){}public static Singleton getSingleton(){if (singleton == null) {synchronized (Singleton.class) {if (singleton == null) {singleton = new Singleton();}}}return singleton;}
}

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