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Java Heap Space vs. Stack Memory | @CloudExpo #JVM #JRE #Java #AI #DX

Stack and heap are two ways Java allocates memory. Understanding when and how they work is critical

Java Heap Space vs. Stack Memory: How Java Applications Allocate Memory
By Angela Stringfellow

Java applications need a certain amount of RAM on a computer to run. Each time an object or variable is declared, it needs more RAM. Simply designating enough memory to hold every value declared and run each method would lead to a bloated application.

To keep application memory requirements lean, it is partitioned in ways that require less memory and allows the application to run more quickly.

The Java Virtual Machine (JVM) divides memory between Java Heap Space and Java Stack Memory in a way that only uses memory that's needed.

What Is Java Heap Space
It is created by the Java Virtual Machine when it starts. The memory is used as long as the application is running. Java runtime uses it to allocate memory to objects and Java Runtime Environment (JRE) classes.

When an object is created, it is always created in Heap and has global access. That means all objects can be referenced from anywhere in the application.

It is managed by two concepts: Garbage collection and young-generation, old-generation.

Garbage collection works to free memory by clearing any by objects without any references in the methods. These are objects that are no longer being used. Clearing them ensures they don't take up space in the Heap.

Young-generation, old-generation helps prioritize objects for garbage collection by dividing Java Heap Space into two generations.

The nursery is the younger generation where the new objects are stored. When the nursery is full, garbage collection cleans it out. Note only the memory space for the nursery is full. There is still memory in the old generation.

The old generation is home to objects have been around long enough. When the old generation runs out of room, garbage collection removes the objects not being used in the old space. Again, only part of the Heap is full when old garbage collection happens. There is still room in the nursery.

What Is Java Stack Memory?
This is the temporary memory where variable values are stored when their methods are invoked. After the method is finished, the memory containing those values is cleared to make room for new methods.

When a new method is invoked, a new block of memory will be created in the Stack. This new block will store the temporary values invoked by the method and references to objects stored in the Heap that are being used by the method.

Any values in this block are only accessible by the current method and will not exist once it ends.

When the method ends, that block will be erased. The next method invoked will use that empty block.

This "last in, first out" method makes it easy to find the values needed and allows fast access to those values.

How They're Used in a Java Application
Let's look at a very simple example of a Java application to see how memory is allocated.

package com.journaldev.test;package com.journaldev.test;
public class Memory {
public static void main(String[] args) { // Line 1 int i=1; // Line 2 Object obj = new Object(); // Line 3 Memory mem = new Memory(); // Line 4 mem.foo(obj); // Line 5 } // Line 9
private void foo(Object param) { // Line 6 String str = param.toString(); //// Line 7
System.out.println(str); } // Line 8
}

In the above example from JournalDev.com, the use of Stack and Heap is explained as follows:

  • All Runtime classes are loaded into the Heap Space when the program is run.
  • Java Runtime creates Stack memory to be used by main() method thread when it is found at line 1. At line 2, a primitive local variable is created, which is stored in the Stack memory of main() method.
  • Since an Object is created at line 3, it's created in Heap memory and the reference for it is stored in Stack memory. At line 4, a similar process occurs when a Memory object is created.
  • When foo() method is called at line 5, a block in the top of the Stack is created for it. Since Java is pass by value, a new reference to Object is created in the foo() stack block in line 6.
  • At line 7, a string is created, which goes in the String Pool in the Heap space, while a reference for it is created in the foo() stack space. At line 8, foo() method is terminated, and the memory block allocated for it in the Stack is freed.
  • Finally, at line 9, main() method terminates, and the Stack memory created for it is destroyed. Because the program ends at this line, Java Runtime frees all the memory and ends the execution of the program.

Key Differences

  • Java Heap Space is used throughout the application, but Stack is only used for the method - or methods - currently running.
  • The Heap Space contains all objects are created, but Stack contains any reference to those objects.
  • Objects stored in the Heap can be accessed throughout the application. Primitive local variables are only accessed the Stack Memory blocks that contain their methods.
  • Memory allocation in the Heap Space is accessed through a complex, young-generation, old-generation system. Stack is accessed through a last-in, first-out (LIFO) memory allocation system.
  • Heap Space exists as long as the application runs and is larger than Stack, which is temporary, but faster.

Additional Resources and Tutorials

To learn more, check out the following resources:

Stack and heap are two ways Java allocates memory. Understanding when and how they work is critical for developing better Java programs.

The post Java Heap Space vs. Stack Memory: How Java Applications Allocate Memory appeared first on Stackify.

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DevOps at Cloud Expo taking place October 31 - November 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA, will feature technical sessions from a rock star conference faculty and the leading industry players in the world.

Must Watch Video: Recap of @DevOpsSummit New York Javits Center

The widespread success of cloud computing is driving the DevOps revolution in enterprise IT. Now as never before, development teams must communicate and collaborate in a dynamic, 24/7/365 environment. There is no time to wait for long development cycles that produce software that is obsolete at launch. DevOps may be disruptive, but it is essential.

Nutanix DevOps Booth at @DevOpsSummit New York Javits Center

DevOps at Cloud Expo will expand the DevOps community, enable a wide sharing of knowledge, and educate delegates and technology providers alike. Recent research has shown that DevOps dramatically reduces development time, the amount of enterprise IT professionals put out fires, and support time generally. Time spent on infrastructure development is significantly increased, and DevOps practitioners report more software releases and higher quality. Sponsors of DevOps at Cloud Expo will benefit from unmatched branding, profile building and lead generation opportunities through:

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For more information on sponsorship, exhibit, and keynote opportunities, contact Carmen Gonzalez by email at events (at) sys-con.com, or by phone 201 802-3021.

Most Popular Video: Sheng Liang's Containers Talk

@DevOpsSummit at Cloud Expo taking place October 31 - November 2, 2017, Santa Clara Convention Center, CA, and is co-located with the 21st International Cloud Expo and will feature technical sessions from a rock star conference faculty and the leading industry players in the world.

@DevOpsSummit 2017 Silicon Valley
(October 31 - November 2, 2017, Santa Clara Convention Center, CA)

@DevOpsSummit 2018 New York 
(June 12-14, 2018, Javits Center, Manhattan)

With major technology companies and startups seriously embracing Cloud strategies, now is the perfect time to attend 21st Cloud Expo, October 31 - November 2, 2017, at the Santa Clara Convention Center, CA, and June 12-14, 2018, at the Javits Center in New York City, NY, and learn what is going on, contribute to the discussions, and ensure that your enterprise is on the right path to Digital Transformation.

Track 1. Enterprise Cloud | Cloud-Native
Track 2.
Big Data | Analytics
Track 3. Internet of Things | IIoT | Smart Cities

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Track 6.
AI | ML | DL | Cognitive
Track 7.
Containers | Microservices | Serverless
Track 8. FinTech | InsurTech | Token Economy

Speaking Opportunities

The upcoming 21st International @CloudExpo@ThingsExpo, October 31 - November 2, 2017, Santa Clara Convention Center, CA, and June 12-14, 2018, at the Javits Center in New York City, NY announces that its Call For Papers for speaking opportunities is open. Themes and topics to be discussed include:

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Submit your speaking proposal today! ▸ Here

Cloud Expo | @ThingsExpo 2017 Silicon Valley
(October 31 - November 2, 2017, Santa Clara Convention Center, CA)

Cloud Expo | @ThingsExpo 2018 New York 
(June 12-14, 2018, Javits Center, Manhattan)

Download Show Prospectus ▸ Here

Every Global 2000 enterprise in the world is now integrating cloud computing in some form into its IT development and operations. Midsize and small businesses are also migrating to the cloud in increasing numbers.  

Companies are each developing their unique mix of cloud technologies and services, forming multi-cloud and hybrid cloud architectures and deployments across all major industries. Cloud-driven thinking has become the norm in financial services, manufacturing, telco, healthcare, transportation, energy, media, entertainment, retail and other consumer industries, and the public sector.

Cloud Expo is the single show where technology buyers and vendors can meet to experience and discus cloud computing and all that it entails. Sponsors of Cloud Expo will benefit from unmatched branding, profile building and lead generation opportunities through:

  • Featured on-site presentation and ongoing on-demand webcast exposure to a captive audience of industry decision-makers.
  • Showcase exhibition during our new extended dedicated expo hours
  • Breakout Session Priority scheduling for Sponsors that have been guaranteed a 35-minute technical session
  • Online advertising in SYS-CON's i-Technology Publications
  • Capitalize on our Comprehensive Marketing efforts leading up to the show with print mailings, e-newsletters and extensive online media coverage.
  • Unprecedented PR Coverage: Editorial Coverage on Cloud Computing Journal.
  • Tweetup to over 75,000 plus followers
  • Press releases sent on major wire services to over 500 industry analysts.

For more information on sponsorship, exhibit, and keynote opportunities, contact Carmen Gonzalez by email at events (at) sys-con.com, or by phone 201 802-3021.

The World's Largest "Cloud Digital Transformation" Event

@CloudExpo | @ThingsExpo 2017 Silicon Valley
(Oct. 31 - Nov. 2, 2017, Santa Clara Convention Center, CA)

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(June 12-14, 2018, Javits Center, Manhattan)

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Sponsorship Opportunities

Sponsors of Cloud Expo | @ThingsExpo will benefit from unmatched branding, profile building and lead generation opportunities through:

  • Featured on-site presentation and ongoing on-demand webcast exposure to a captive audience of industry decision-makers
  • Showcase exhibition during our new extended dedicated expo hours
  • Breakout Session Priority scheduling for Sponsors that have been guaranteed a 35 minute technical session
  • Online targeted advertising in SYS-CON's i-Technology Publications
  • Capitalize on our Comprehensive Marketing efforts leading up to the show with print mailings, e-newsletters and extensive online media coverage
  • Unprecedented Marketing Coverage: Editorial Coverage on ITweetup to over 100,000 plus followers, press releases sent on major wire services to over 500 industry analysts

For more information on sponsorship, exhibit, and keynote opportunities, contact Carmen Gonzalez (@GonzalezCarmen) today by email at events (at) sys-con.com, or by phone 201 802-3021.

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All major researchers estimate there will be tens of billions devices - computers, smartphones, tablets, and sensors - connected to the Internet by 2020. This number will continue to grow at a rapid pace for the next several decades.

With major technology companies and startups seriously embracing Cloud strategies, now is the perfect time to attend @CloudExpo@ThingsExpo, October 31 - November 2, 2017, at the Santa Clara Convention Center, CA, and June 12-4, 2018, at the Javits Center in New York City, NY, and learn what is going on, contribute to the discussions, and ensure that your enterprise is on the right path to Digital Transformation.

Delegates to Cloud Expo | @ThingsExpo will be able to attend 8 simultaneous, information-packed education tracks.

There are over 120 breakout sessions in all, with Keynotes, General Sessions, and Power Panels adding to three days of incredibly rich presentations and content.

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Financial Technology - or FinTech - Is Now Part of the @CloudExpo Program!

Accordingly, attendees at the upcoming 21st Cloud Expo | @ThingsExpo October 31 - November 2, 2017, Santa Clara Convention Center, CA, and June 12-14, 2018, at the Javits Center in New York City, NY, will find fresh new content in a new track called FinTech, which will incorporate machine learning, artificial intelligence, deep learning, and blockchain into one track.

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More than US$20 billion in venture capital is being invested in FinTech this year. @CloudExpo is pleased to bring you the latest FinTech developments as an integral part of our program, starting at the 21st International Cloud Expo October 31 - November 2, 2017 in Silicon Valley, and June 12-14, 2018, in New York City.

@CloudExpo is accepting submissions for this new track, so please visit www.CloudComputingExpo.com for the latest information.

About SYS-CON Media & Events

SYS-CON Media (www.sys-con.com) has since 1994 been connecting technology companies and customers through a comprehensive content stream - featuring over forty focused subject areas, from Cloud Computing to Web Security - interwoven with market-leading full-scale conferences produced by SYS-CON Events. The company's internationally recognized brands include among others Cloud Expo® (@CloudExpo), Big Data Expo® (@BigDataExpo), DevOps Summit (@DevOpsSummit), @ThingsExpo® (@ThingsExpo), Containers Expo (@ContainersExpo) and Microservices Expo (@MicroservicesE).

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