【并发编程】延时初始化

不安全的延时初始化：
/** * Unsafe lazy initialization
*/@NotThreadSafepublic class UnsafeLazyInitialization { private static Resource resource;
//resource的赋值可能和Resource()域的赋值 顺序重排序 public static Resource getInstance() { if (resource == null) resource = new Resource(); // unsafe publication return resource; } static class Resource { }}线程not-safe说明：


安全的延时初始化/**
* Thread-safe lazy initialization*/
@ThreadSafepublic class SafeLazyInitialization { private static Resource resource; public synchronized static Resource getInstance() { if (resource == null) resource = new Resource(); return resource; } static class Resource { }}安全的延时初始化延时初始化占位符模式--使用static初始化--不需要显示的同步/**
* Lazy initialization holder class idiom
*/
@ThreadSafepublic class ResourceFactory { private static class ResourceHolder { //使用static静态初始化（关键） public static Resource resource = new Resource(); } //当任何一个线程在首次调用getResource()时，都会使ResourceHolder被加载和被初始化 public static Resource getResource() { return ResourceFactory.ResourceHolder.resource; }}

来自为知笔记(Wiz)