How to identify default Java heapsize in Windows

Question

Im running an eclipse application in my machine. I have two queries

1. I would like to know how to check the default heap size that the jvm is using to run the application.I'm using a windows machine to run the java application. I tried to check the default heap size by the following way

ControlPanel--->Programs--->JavaSetting--> JavaTab -->View Button ---> JavaRuntimeEnvironment settings window ---> Userstab --> Value under RuntimeParameters

But in my system, there is no runtime parameters defined. Is there a command that I can execute via command prompt to check the default heap size in my machine.

2. How to increase the heap size parameter and run the eclipse plugin application from command prompt. For eg: To increase the heap size and execute the jar file we use the below command java -Xms64m -jar MyApp.jar. I would like to know how to set heap parameters and execute my java application which is an exe file. I tried to execute use the below command, but the command prompt doesn't recognize the command

   java -Xms512m iepsd.exe

Where iepsd.exe is my java application.

Answer 1

You can use -XX:+PrintFlagsFinal to print out a huge list of internal options to the JVM once all command line arguments and defaults have been processed. The -Xms option corresponds to InitialHeapSize, and the -Xmx option corresponds to MaxHeapSize.

To find the default maximum heap size that the JVM is using on Windows, run:

javaw -XX:+PrintFlagsFinal | find "MaxHeapSize"

To find the default initial heap size, run:

javaw -XX:+PrintFlagsFinal | find "InitialHeapSize"

Answer 2

try below command for detailed result

java -XX:+PrintFlagsFinal -version | findstr /i "HeapSize PermSize ThreadStackSize"

result is

C:\Users\amar.magar>java -XX:+PrintFlagsFinal -version | findstr /i "HeapSize PermSize ThreadStackSize"
 intx CompilerThreadStackSize                   = 0                                   {pd product}
uintx ErgoHeapSizeLimit                         = 0                                   {product}
uintx HeapSizePerGCThread                       = 87241520                            {product}
uintx InitialHeapSize                          := 268435456                           {product}
uintx LargePageHeapSizeThreshold                = 134217728                           {product}
uintx MaxHeapSize                              := 4271898624                          {product}
 intx ThreadStackSize                           = 0                                   {pd product}
 intx VMThreadStackSize                         = 0                                   {pd product}

java version "1.8.0_121"
Java(TM) SE Runtime Environment (build 1.8.0_121-b13)
Java HotSpot(TM) 64-Bit Server VM (build 25.121-b13, mixed mode)

Answer 3

To answer the below query of vr3w3c9

Query raised by vr3w3c9: Hi, Thanks for the response. I tried to execute the above command javaw -XX:+PrintFlagsFinal | find "InitialHeapSize" in the command prompt, the value is not getting displayed. Im getting a popup message which says:

could not create the java Virtual Machine – vr3w3c9 Sep 27 '13 at 4:54

Answer: In Windows machine, Please run/open the Command Prompt (Windows Command Processor) as Administrator and execute the command you have mentioned. you will get the result as shown below:

C:\windows\system32>javaw -XX:+PrintFlagsFinal | find "MaxHeapSize"

uintx MaxHeapSize                              := 2122317824      {product}

C:\windows\system32>javaw -XX:+PrintFlagsFinal | find "InitialHeapSize"

uintx InitialHeapSize                          := 132531136       {product}

Here, the unit of MaxHeapSize and InitialHeapSize is bytes.

Answer 4

Use JConsole. It is shipped with the JDK. You will find it's executable in the corresponding bin directory.