Linux OpenJDK 时区问题， offset=-18000000 等于-0400？？？

如果我没记错的话：

1. 预装的是东八区(+0800)的时间，CST-8
2. 安装 OpenJDK 1.8 （不记得是否预装的
3. 发现时区问题后我mv /etc/localtime /etc/localtime_bak把时区改成 UTC

import java.text.SimpleDateFormat;
import java.util.Date;
import java.util.TimeZone;

public class Main {

    public static void main(String[] args) {
        System.out.println(TimeZone.getDefault());
        System.out.println(new SimpleDateFormat("yyyy-MM-dd HH:mm:ss ZZ").format(new Date()));
    }

}

 ~> java -version
openjdk version "1.8.0_181"
OpenJDK Runtime Environment (build 1.8.0_181-8u181-b13-2~deb9u1-b13)
OpenJDK 64-Bit Server VM (build 25.181-b13, mixed mode)
 ~> cat /etc/localtime
cat: /etc/localtime: No such file or directory
 ~> date -R
Wed, 13 Mar 2019 10:00:03 +0000
 ~> cat /etc/issue
Debian GNU/Linux 9 \n \l

 ~> java Main
sun.util.calendar.ZoneInfo[id="US/Eastern",offset=-18000000,dstSavings=3600000,useDaylight=true,transitions=235,lastRule=java.util.SimpleTimeZone[id=US/Eastern,offset=-18000000,dstSavings=3600000,useDaylight=true,startYear=0,startMode=3,startMonth=2,startDay=8,startDayOfWeek=1,startTime=7200000,startTimeMode=0,endMode=3,endMonth=10,endDay=1,endDayOfWeek=1,endTime=7200000,endTimeMode=0]]
2019-03-13 06:02:54 -0400

问题:

1. openjdk 默认时区不读系统时区的吗？（有看到网上说 openjdk 不读/etc/localtime文件的，那怎么配置默认时区？不要命令行传参或代码里setDefault
2. offset=-18000000 和-0400 不对吧，-18000000/3600000 不是-5 么？