GarbageCollectorMXBean: Extract information about garbage collection

‘GarbageCollectorMXBean’ class provides information about the total number of collections that have occurred, approximate accumulated collection elapsed time in milli seconds etc.,

Example

private static void printGarbageCollectorBeansInfo() {

         System.out.println("---------------------------------------------");

         List<GarbageCollectorMXBean> beans = ManagementFactory.getGarbageCollectorMXBeans();

         for (GarbageCollectorMXBean bean : beans) {

                  System.out.println("Name : " + bean.getName());

                  System.out.println("Collection Count : " + bean.getCollectionCount());

                  System.out.println("Collection Time : " + bean.getCollectionTime());

                  String[] memoryPoolNames = bean.getMemoryPoolNames();

                  for (String poolName : memoryPoolNames) {

                           System.out.println(poolName);

                  }

         }

         System.out.println("---------------------------------------------");

}

App.java

import java.lang.management.GarbageCollectorMXBean;
import java.lang.management.ManagementFactory;
import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.TimeUnit;

public class App {

 private static class BigObject {
  int i;
  int ii;
  int iii;
  int iiii;
  int iiiii;
  int iiiiii;
  int iiiiiii;
  int iiiiiiii;
  int iiiiiiiii;
  int iiiiiiiiii;

  public BigObject() {
   i = 1;
   ii = 11;
   iii = 111;
   iiii = 1111;
   iiiii = 11111;
   iiiiii = 111111;
   iiiiiii = 1111111;
   iiiiiiii = 11111111;
   iiiiiiiii = 111111111;
   iiiiiiiiii = 1111111111;
  }

 }

 private static void printGarbageCollectorBeansInfo() {
  System.out.println("---------------------------------------------");
  List<GarbageCollectorMXBean> beans = ManagementFactory.getGarbageCollectorMXBeans();

  for (GarbageCollectorMXBean bean : beans) {
   System.out.println("Name : " + bean.getName());
   System.out.println("Collection Count : " + bean.getCollectionCount());
   System.out.println("Collection Time : " + bean.getCollectionTime());

   String[] memoryPoolNames = bean.getMemoryPoolNames();
   for (String poolName : memoryPoolNames) {
    System.out.println(poolName);
   }

  }
  System.out.println("---------------------------------------------");
 }

 public static void main(String args[]) throws InterruptedException {

  int counter = 0;
  
  List<BigObject> bigObjs = new ArrayList<> ();

  while (true) {
   BigObject obj = new BigObject();
   
   counter++;
   
   bigObjs.add(obj);
   
   //System.out.println(counter);

   if (counter % 1000000 == 0) {
    bigObjs = new ArrayList<> ();
    counter = 0;
    TimeUnit.SECONDS.sleep(5);
    printGarbageCollectorBeansInfo();
   }
  }

 }
}

Run App.java by executing below command.

java -Xmx512M App

You can see following kind of output.

---------------------------------------------
Name : PS Scavenge
Collection Count : 1
Collection Time : 30
PS Eden Space
PS Survivor Space
Name : PS MarkSweep
Collection Count : 0
Collection Time : 0
PS Eden Space
PS Survivor Space
PS Old Gen
---------------------------------------------
---------------------------------------------
Name : PS Scavenge
Collection Count : 2
Collection Time : 56
PS Eden Space
PS Survivor Space
Name : PS MarkSweep
Collection Count : 0
Collection Time : 0
PS Eden Space
PS Survivor Space
PS Old Gen
---------------------------------------------
---------------------------------------------
Name : PS Scavenge
Collection Count : 2
Collection Time : 56
PS Eden Space
PS Survivor Space
Name : PS MarkSweep
Collection Count : 0
Collection Time : 0
PS Eden Space
PS Survivor Space
PS Old Gen
---------------------------------------------
---------------------------------------------
Name : PS Scavenge
Collection Count : 3
Collection Time : 78
PS Eden Space
PS Survivor Space
Name : PS MarkSweep
Collection Count : 0
Collection Time : 0
PS Eden Space
PS Survivor Space
PS Old Gen
---------------------------------------------

Try to run the same application with different garbage collectors.

$java -Xmx512M -XX:+UseConcMarkSweepGC App 
---------------------------------------------
Name : ParNew
Collection Count : 1
Collection Time : 149
Par Eden Space
Par Survivor Space
Name : ConcurrentMarkSweep
Collection Count : 0
Collection Time : 0
Par Eden Space
Par Survivor Space
CMS Old Gen
---------------------------------------------

$java -Xmx512M -XX:+UseSerialGC App 
---------------------------------------------
Name : Copy
Collection Count : 1
Collection Time : 69
Eden Space
Survivor Space
Name : MarkSweepCompact
Collection Count : 0
Collection Time : 0
Eden Space
Survivor Space
Tenured Gen
---------------------------------------------

$java -Xmx512M -XX:+UseG1GC App 
---------------------------------------------
Name : G1 Young Generation
Collection Count : 3
Collection Time : 60
G1 Eden Space
G1 Survivor Space
Name : G1 Old Generation
Collection Count : 0
Collection Time : 0
G1 Eden Space
G1 Survivor Space
G1 Old Gen
---------------------------------------------

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