JVM ( java virtual machine) architecture - tutorial

In this video I tried to explore one of the popular core Java interview topics - Java virtual machine architecture - this provides you a fairly detailed walk through, also touches up on topics such as permgen and metaspace( jdk8) - I am going to post more topics like these, hit subscribe if you like what you see.
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[vyshnavramesh]

0:49 Edit .java -> compile .java -> run .class
3:33 JVM breakdown
4:14 Class loader: load (bootstrap (rt.jar), extension (jre/lib/ext), application (classes we write))
6:59 Class loader: link (verify bytecode, prepare memory allocation for static variables, resolve nested references of a class)
10:02 Class loader: initialize (of static variables, static blocks)
11:09 ClassNotFoundException and ClassDefNotFoundException
12:38 Runtime Data area
13:01 Method Area / Permgen space / Metaspace (class data like static variables)
16:16 Heap (object data)
17:41 Program Counter Register: pointer to next instruction to be executed per thread
18:35 Java Stacks: stack frame of currently running method per thread
20:16 Native method stack: for running non-java methods called from java methods running in Java Stack (per thread)
24:09 Execution engine: GHIJ (Garbage Collector, Hotspot Profiler, Interpreter, JOT Compiler)
24:26 Interprets and executes the bytecode/instruction
25:52 JIT Compiler: Bytecodes that are repeated, called hotspots, are saved from re-interpretation. On the fly compiles them and make them ready for execution
26:27: Hotspot Profiler: graphically analyses the all the bytecodes and helps JIT compiler
27:36 Recap
26:57 Garbage Collector: cleans up unused classes, objects and memory areas.

[devsatg]

Man, I have already watched this video like 5 times and I keep coming back to refresh. Kudos

[samirpanchal]

your channel helped me understood some important concepts of java, Thanks for your support and keep educating people around.

[akshatvashishtha]

Hi Ranjith this the most absolute extent about internal working of JVM.. Your work is reverence.. Such a deep & cultured explanation on JVM.. Generally, I never write on anything but your video convinced me to share my thoughts.. Great work, it's too helpful..

[eswarprasad]

Thanks for this video,
I cleared 3 rounds of interview and got rejected in the final round because I couldnt explain memory management in jvm
yes companies in india do ask about jvm.this video will help me for my next interview.

[baobozo]

Great tutorial man~ Best thing I've ever found to have JVM explained so clearly in such a simple way.

[dmitrikonnov]

Matter of fact, to know how jvm works is terrifically important, this topic hasn't been covered enough though unlike all other fancy stuff. Thumbs up!

[jvsnyc]

This is still great after 5+ years. The Bootstrap loading is somewhat different in the most recent versions of Java, they broke up rt.jar into modules which aren't covered here because they didn't exist back in Java 8...

[AbdelmuniemAbdallah]

Well Explained in a simple way, I have understood now how JVM is working.
Thanks a lot.

[smuralimohan]

Excellent video... never seen a better one on JVM. Thanks a lot!

[enjoywithvivin]

Excellent and very helpful to explore lot about JVM. Thanks.

[mailmahendran]

Awesome presentation with all the images. Thanks and awaiting more of your videos.

[hp]

Sir, Thank you for sharing your deep insight on this subject. After several years of struggling through understanding JVM concepts, this video today has finally helped me!!!

[RanjitRajD]

Simple words explained very complicated architecture.
Thanks for your good effort. Keep going. We are now big fan of your videos.

[arnabthakuria]

Amazing tutorial, sir . Thanks for sharing your knowledge.

[akshayyhakrishnamurthy]

One of the best videos with clear explanation. Helps me understand the basics. Thank you for making this video. Its really helpful! Good work...

[tatyanav]

despite slightly outdated it's one of the best videos I've went through, perfect to start with

[deepikar]

An amazing video Ranjith! Just what I was looking for!! But I have few questions that are requesting some insights :

1) Does loading bytecodes into memory == simply copying them to RAM for further processing?

2) In the class loader -> "verify" step, what are the examples of "bad/invalid" bytecode? What error is raised if the bytecode is not valid?

3) In class loader -> "Prepare step", what is the intent behind performing memory allocation for class member variables and later assign the values for static ones?

4) In Application loader aren't the different class files created by us required to be given if not existing in the current same directory? So if the classes are already loaded in the Application Loader phase, what happens in the "Resolve" phase?

5) Does interpreter convert bytecode to macine code? And JIT caches the frequent machine codes?

6) Could Native method calls be the calls to OS to allocate memory, handle resources? If no, what are some examples ?

I know these are too many but please help out!!

[javedakhtar-omhb]

Lovely Presentation with key points of the JVM architecture.

[rahulpatil]

very good explained sir all dout clear no 1 video thanks so much