java单例模式

1、什么时候使用单例模式？

* 单例防止CPU、内存资源浪费；多例防止并发，例如action；

* 频繁的调用，使用单例，防止资源浪费

* 即节约资源，又便于维护，保证只有一个实例

2、java单例写法

/**
 * Returns the single instance of this class, creating it if necessary. * * @return the {@link PeopleInfoService} instance */public static PeopleInfoService getInstance() {    if (INSTANCE == null) {        INSTANCE = new PeopleInfoService();    }    return INSTANCE;}/** * Used to force {@link #getInstance()} to create a new instance * next time it's called. */public static void destroyInstance() {    INSTANCE = null;}