启动 JVM 时，-Xms 和 - Xmx 参数是什么？

请说明Xms和Xmx参数的用法。它们的默认值是多少？

java -Xms256m -Xmx2048m

-Xmx1024k
-Xmx512m
-Xmx8g

C:\Users\Admin>java -X
-Xmixed           mixed mode execution (default)
-Xint             interpreted mode execution only
-Xbootclasspath:<directories and zip/jar files separated by ;>
                      set search path for bootstrap classes and resources
-Xbootclasspath/a:<directories and zip/jar files separated by ;>
                      append to end of bootstrap class path
-Xbootclasspath/p:<directories and zip/jar files separated by ;>
                      prepend in front of bootstrap class path
-Xdiag            show additional diagnostic messages
-Xnoclassgc       disable class garbage collection
-Xincgc           enable incremental garbage collection
-Xloggc:<file>    log GC status to a file with time stamps
-Xbatch           disable background compilation
-Xms<size>        set initial Java heap size.........................
-Xmx<size>        set maximum Java heap size.........................
-Xss<size>        set java thread stack size
-Xprof            output cpu profiling data
-Xfuture          enable strictest checks, anticipating future default
-Xrs              reduce use of OS signals by Java/VM (see documentation)
-Xcheck:jni       perform additional checks for JNI functions
-Xshare:off       do not attempt to use shared class data
-Xshare:auto      use shared class data if possible (default)
-Xshare:on        require using shared class data, otherwise fail.
-XshowSettings    show all settings and continue
-XshowSettings:all         show all settings and continue
-XshowSettings:vm          show all vm related settings and continue
-XshowSettings:properties  show all property settings and continue
-XshowSettings:locale      show all locale related settings and continue

您可以在 IDE 中指定它。例如，对于 Eclipse 中的运行配置 → VM 参数 。您可以输入-Xmx800m -Xms500m作为

在此处输入图片说明

上面已经解决了这个问题。仅添加部分默认值。

按照http://docs.oracle.com/cd/E13150_01/jrockit_jvm/jrockit/jrdocs/refman/optionX.html

Xmx 的默认值将取决于平台和系统中可用的内存量。

-Xmx<size> - to set the maximum Java heap size
-Xms<size> - to set the initial Java heap size

java -Xms256m -Xmx4g

-Xms用于启动的初始堆大小，但是，在工作过程中，由于用户不活动或 GC 迭代，堆大小可能小于-Xms 。这不是最小的必需堆大小。

-Xmx最大堆大小

答案