读《研磨设计模式》-代码笔记-单例模式

bylijinnan

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public class Singleton {}class LazySingleton{private static LazySingleton instance;public static LazySingleton getInstance() {if (instance == null) {instance = new LazySingleton();}return instance;}private LazySingleton(){}}/* * 双重锁模式  * 1.比起单纯的"public static synchronized LazySecureSingleton getInstance()"要快 * 2.但volatile的使用需要小心。已经建议不使用volatile关键字了 */class LazySecureSingleton{private volatile static LazySecureSingleton instance;public static LazySecureSingleton getInstance() {if (instance == null) {synchronized (LazySecureSingleton.class){if (instance == null) {instance = new LazySecureSingleton();}}}return instance;}private LazySecureSingleton(){}}class EagerSingleton{private static EagerSingleton instance = new EagerSingleton();public static EagerSingleton getInstance() {return instance;}private EagerSingleton(){}}/* * 使用静态内部类 * 利用“静态内部类只有在被使用时才装载”的特性 */class InnerStaticClassSingleton{private static class SingletonHolder {private static InnerStaticClassSingleton instance = new InnerStaticClassSingleton();}public static InnerStaticClassSingleton getInstance() {return SingletonHolder.instance;}private InnerStaticClassSingleton(){}}/* * 用枚举来实现单例 <Effective Java>里面认为这是实现单例的最好方法 */enum EnumSingleton{INSTANCE;}