View / Set JVM use garbage collector

First, set the parameters of the garbage collector

　　-XX: + UseSerialGC, the default value of the virtual machine in the Client mode, Serial + Serial Old

　　-XX: + UseParNewGC, ParNew + Serial Old, In JDK1.8 has been deprecated and will be removed (Java HotSpot (TM) Client VM warning: Using the ParNew young collector with the Serial old collector is deprecated and will likely be removed in a future release).

　　-XX:+UseConcMarkSweepGC，ParNew+CMS

　　-XX: + UseParallelGC, the default value of the virtual machine in the Server mode, Parallel Scavenge + Serial Old

　　-XX:+UseParallelOldGC ，Parallel Scavenge+Parallel Old

　　-XX:+UseG1GC，G1 Young Generation+G1 Old Generation

Second, the use of Java code testing

{class GCTest public 
    public static void main (String [] args) { 
        // - XX: + UseParallelOldGC and -XX: + UseParallelGC As a result, since MXBean name, but not the same as actually used 
        List <GarbageCollectorMXBean> garbageCollectorMXBeans = ManagementFactory. getGarbageCollectorMXBeans (); 
        for (GC of GarbageCollectorMXBean: garbageCollectorMXBeans) { 
            System.out.println (gc.getName ()); 
            System.out.println ( "-"); 
        } 
    } 
}

I use JDK1.8 test here, enter the JVM startup parameters -XX: + PrintCommandLineFlags, this parameter will print JVM default optimization parameters.

Test Results:

　　1, specify the parameters -XX: + PrintCommandLineFlags -XX: + UseSerialGC

-XX:InitialHeapSize=16777216 -XX:MaxHeapSize=268435456 -XX:+PrintCommandLineFlags -XX:-UseLargePagesIndividualAllocation -XX:+UseSerialGC 
Copy
--
MarkSweepCompact
--

　　2, specify the parameters -XX: + PrintCommandLineFlags -XX: + UseParNewGC

-XX:InitialHeapSize=16777216 -XX:MaxHeapSize=268435456 -XX:+PrintCommandLineFlags -XX:-UseLargePagesIndividualAllocation -XX:+UseParNewGC 
ParNew
--
MarkSweepCompact
--
Java HotSpot(TM) Client VM warning: Using the ParNew young collector with the Serial old collector is deprecated and will likely be removed in a future release

　　3, specify the parameters -XX: + PrintCommandLineFlags -XX: + UseConcMarkSweepGC

-XX:InitialHeapSize=16777216 -XX:MaxHeapSize=268435456 -XX:MaxNewSize=89481216 -XX:MaxTenuringThreshold=6 -XX:OldPLABSize=16 -XX:+PrintCommandLineFlags -XX:+UseConcMarkSweepGC -XX:-UseLargePagesIndividualAllocation -XX:+UseParNewGC 
ParNew
--
ConcurrentMarkSweep
--

　　4, specify the parameters -XX: + PrintCommandLineFlags -XX: + UseParallelGC

-XX:InitialHeapSize=16777216 -XX:MaxHeapSize=268435456 -XX:+PrintCommandLineFlags -XX:-UseLargePagesIndividualAllocation -XX:+UseParallelGC 
PS Scavenge
--
PS MarkSweep
--

　　5, specify the parameters -XX: + PrintCommandLineFlags -XX: + UseParallelOldGC

-XX:InitialHeapSize=16777216 -XX:MaxHeapSize=268435456 -XX:+PrintCommandLineFlags -XX:-UseLargePagesIndividualAllocation -XX:+UseParallelOldGC 
PS Scavenge
--
PS MarkSweep
--

　　6, specify the parameters -XX: + PrintCommandLineFlags -XX: + UseG1GC

-XX:InitialHeapSize=16777216 -XX:MaxHeapSize=268435456 -XX:+PrintCommandLineFlags -XX:+UseG1GC -XX:-UseLargePagesIndividualAllocation 
G1 Young Generation
--
G1 Old Generation
--

Third, use the built-JConsle View

　　1, write a code that has been run

public class GCTest {
    public static void main(String[] args) throws InterruptedException {
        while (true) {
            Thread.sleep(1000); 
        }
    }
}   

　　2, open a command line, enter jconsole

　　3, showing the connection of a Java program

　　4, see the VM Summary

　　5, can also be viewed in the MBean

IV Summary

　　-XX: + UseParallelGC and -XX: + UseParallelOldGC addition to the different JVM parameters, print results are the same, because the same set MXBean name, specific can look at this article: https: //www.cnblogs.com/kelthuzadx /p/10924117.html