单例模式

class LogUtil{
public static LogUtil getInstance() {  
    if (sLogUtil == null) {  
        synchronized (LogUtil.class) {  
            if (sLogUtil == null) {  
                sLogUtil = new LogUtil();  
            }  
        }  
    }  
    return sLogUtil;  
}
}

 加双重同步锁，防止多线实例化