Oracle HotSpot JVM Command Line Flags

Find information about all the Oracle HotSpot JVM Command Line Flags:

• http://docs.oracle.com/javase/8/docs/technotes/tools/unix/java.html
• http://www.oracle.com/technetwork/java/javase/tech/vmoptions-jsp-140102.html

One can use -XX:+PrintCommandLineFlags to see the default command line flags. For example

C:\>java -XX:+PrintCommandLineFlags -version

-XX:InitialHeapSize=263467392 -XX:MaxHeapSize=4215478272 -XX:+PrintCommandLineFlags 
-XX:+UseCompressedClassPointers -XX:+UseCompressedOops -XX:-UseLargePagesIndividualAllocation 
-XX:+UseParallelGC
java version "1.8.0"
Java(TM) SE Runtime Environment (build 1.8.0-b132)
Java HotSpot(TM) 64-Bit Server VM (build 25.0-b70, mixed mode)

tells us that Java 8 uses the Parallell Garbage Collector as a default (-XX:+UseParallelGC) garbage collector, that the default min heap size is 1/64 (263467392 bytes - about 250MB) of my machines RAM (16GB) and the default max heap size is 25% (4215478272 bytes - about 4 GB), of my machines RAM.

One can also find out the value of a specific command line flag using the tool jinfo. For example

C:\>jinfo -flag MaxHeapSize 3216

-XX:MaxHeapSize=4217372672

tells us again the value of the max heap size. 3216 is the process id of the Java process you are interested in. You can find out the process ids of locally running Java processes using the tool jps

C:\>jps

3216 Bootstrap
5872 Jps
2944 org.eclipse.equinox.launcher_1.3.0.v20130327-1440.jar