Java单例模式

private static volatile SettingsDbHelper sInst = null;  // <<< 这里添加了 volatile  public static SettingsDbHelper getInstance(Context context) {      SettingsDbHelper inst = sInst;  // <<< 在这里创建临时变量    if (inst == null) {        synchronized (SettingsDbHelper.class) {            inst = sInst;            if (inst == null) {                inst = new SettingsDbHelper(context);                sInst = inst;            }        }    }    return inst;  // <<< 注意这里只需要返回临时变量}