jmap: Print java heap summary

Below command prints the heap summary of java application.

jmap -heap {PROCESS_ID}

For example,

HelloWorld.java

public class HelloWorld {
 public static void main(String args[]) throws Exception {
  int count = 0;
  
  Thread t1 = new Thread() {
   public void run() {
    while(true){
     try{
      Thread.sleep(2000);
     }catch(Exception e){
      
     }
    }
   }
  };

  t1.start();
 }
}

Compile HelloWorld.java.

Launch HelloWorld application using below command.

java -Xms128m -Xmx1024m -classpath . HelloWorld

Open another command prompt (or) terminal and execute jcmd command.

C:\>jcmd
18612
5556 sun.tools.jcmd.JCmd
21292 HelloWorld

As you see jcmd command output, HelloWorld application is running on port 21292.

Execute the command ‘jmap -heap 21292’ to get the summary of heap memory.

C:\>jmap -heap 21292
Attaching to process ID 21292, please wait...
Debugger attached successfully.
Server compiler detected.
JVM version is 25.171-b11

using thread-local object allocation.
Parallel GC with 4 thread(s)

Heap Configuration:
   MinHeapFreeRatio         = 0
   MaxHeapFreeRatio         = 100
   MaxHeapSize              = 1073741824 (1024.0MB)
   NewSize                  = 44564480 (42.5MB)
   MaxNewSize               = 357564416 (341.0MB)
   OldSize                  = 89653248 (85.5MB)
   NewRatio                 = 2
   SurvivorRatio            = 8
   MetaspaceSize            = 21807104 (20.796875MB)
   CompressedClassSpaceSize = 1073741824 (1024.0MB)
   MaxMetaspaceSize         = 17592186044415 MB
   G1HeapRegionSize         = 0 (0.0MB)

Heap Usage:
PS Young Generation
Eden Space:
   capacity = 34078720 (32.5MB)
   used     = 2045120 (1.95037841796875MB)
   free     = 32033600 (30.54962158203125MB)
   6.001164362980769% used
From Space:
   capacity = 5242880 (5.0MB)
   used     = 0 (0.0MB)
   free     = 5242880 (5.0MB)
   0.0% used
To Space:
   capacity = 5242880 (5.0MB)
   used     = 0 (0.0MB)
   free     = 5242880 (5.0MB)
   0.0% used
PS Old Generation
   capacity = 89653248 (85.5MB)
   used     = 0 (0.0MB)
   free     = 89653248 (85.5MB)
   0.0% used

735 interned Strings occupying 50584 bytes.

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