例子: 这里有一座象牙塔可供巫师学习魔法。所有的巫师都使用同一座象牙塔来附魔。这里的象牙塔就是单例。 */ @Slf4j public class App { public static void main(String[] args) { // 静态成员属性 IvoryTower ivoryTower1 = IvoryTower.getInstance(); IvoryTower ivoryTower2 = IvoryTower.getInstance(); LOGGER.info("ivoryTower1={}", ivoryTower1); LOGGER.info("ivoryTower2={}", ivoryTower2); // DCL 又称双重检测锁机制: 延迟加载静态成员变量 var threadSafeIvoryTower1 = ThreadSafeLazyLoadedIvoryTower.getInstance(); var threadSafeIvoryTower2 = ThreadSafeLazyLoadedIvoryTower.getInstance(); LOGGER.info("threadSafeIvoryTower1={}", threadSafeIvoryTower1); LOGGER.info("threadSafeIvoryTower2={}", threadSafeIvoryTower2); // 枚举 推荐使用 var enumIvoryTower1 = EnumIvoryTower.INSTANCE; var enumIvoryTower2 = EnumIvoryTower.INSTANCE; LOGGER.info("enumIvoryTower1={}", enumIvoryTower1); LOGGER.info("enumIvoryTower2={}", enumIvoryTower2); // DCL 又称双重检测锁机制, 同时使用局部变量提升 25% 的性能 var dcl1 = ThreadSafeDoubleCheckLocking.getInstance(); LOGGER.info(dcl1.toString()); var dcl2 = ThreadSafeDoubleCheckLocking.getInstance(); LOGGER.info(dcl2.toString()); // 静态内部类,支持懒加载，弥补了静态成员变量方式的缺点 var demandHolderIdiom = InitializingOnDemandHolderIdiom.getInstance(); LOGGER.info(demandHolderIdiom.toString()); var demandHolderIdiom2 = InitializingOnDemandHolderIdiom.getInstance(); LOGGER.info(demandHolderIdiom2.toString()); } }