java命令启动参数-Xms -Xmx的问题

这两个参数只是限值Java程序的heap大小，如果你了解heap和stack那么应该知道，一般来说只有运行时动态创建的对象才存在于heap中

$ java -X
    ...
    -Xms<size>        set initial Java `heap size`
    -Xmx<size>        set maximum Java `heap size`
    ...

另外，通过top命令查看到的资源情况是针对整个Java进程的，JVM在执行你的Java代码时还需要载入整个Java Runtime，有自己的开销，这些都不包括在-Xms/-Xmx中

From Oracle's Documentation:

Note that the JVM uses more memory than just the heap. For example
Java methods, thread stacks and native handles are allocated in memory

separate from the heap, as well as JVM internal data structures.