Java memory management pdf

Memory Management with Java and C++

• Local memory is quite automatic — it is allocated automatically on function call and it is deallocated automatically when a function exits.

• Heap Lifetime– Because the programmer now controls

exactly when memory is allocated and deallocated, it is possible to build a data structure in memory, and return that data structure to the caller. This was never possible with local memory which was automatically deallocated when the function exited.

• Allocate 3 GIF images in the heap

each of which takes 1024 bytes of

• both values and the variables are allocated memory. However, each assignment copies into the variable’s block, not the contents of the value block, but instead its address

• both values and the variables are allocated memory. However, each assignment copies into the variable’s block, not the contents of the value block, but instead its address

• we get a NullPointerException (Java)

• we can determine whether the value

of a pointer variable is null or not, and

hence, whether we can access its

• Multiple pointers sharing a value

Point p1 = new ACartesianPoint(50, 50);

• When p1 is assigned to p2, the pointer stored

in p1 is copied into p2, not the object itself.

Both variables share the same object, and thus, the

code will print 100 and not 50, as you might expect.

• Code area– where code to be executed is stored

• Heap– store variables and objects allocated

– accessed with no restrictions

• Execution Stack– perform computation

– perform function call management

accessed with a LIFO policy (Last In First Out)

• C++ has several other memory areas

• C++ the entire code is loaded into

code area, and neglect dynamic

Scope Activation Record (SAR)is put every time a new block is encountered

Scope Activation Record (SAR)

– Local variables (declared inside the

– The Static Link SL (a.k.a SAR link) a pointer to the SAR of the

immediate enclosing block; used to acce

ss local variables of outer blocks from the

Scope Activation Record (SAR)

References and Pointersconceptually the SAME

Classes and ObjectsObjects are instances of classes

Classes and ObjectsObjects are instances of classes

(Objects are classes in action)

• In C++ classes are truly user defined ty

pes. Objects are treated as any other

variable and are allocated:

– On the stack, as regular local variables

// reference hello is on stack, the object is on the

// Java puts this value directly in same slot and doesn’t // create a wrapping object.

Java: Why are wrapper classes needed?http://stackoverflow.com/questions/2134798/java-why-are-wrapper-classes-needed

Java examplepublic class CoffeeMaker

aCoffeeMaker = new CoffeeMaker();

Integer sugarObject = new Integer(3);

Java examplepublic class CoffeeMaker

aCoffeeMaker = new CoffeeMaker();

Integer sugarObject = new Integer(3);

• Java objects can be accessed just

through reference variables, that hold

the address of objects in heap.

CoffeeMaker *aPtrCoffeeMaker = new CoffeeMaker();

aRefCoffeeMaker = *aPtrCoffeeMaker; // dangerous!

Stack and Heap comparison

Issues for objects in memory (Java)

• Objects with no references pointing to

them are considered eligible for

automatic garbage collection by the

system, which runs periodically and

performs the real destruction of the

• GC is not directly under control of the

Issues for objects in memory (C++)

• After an object has been created on

the heap (with the new directive) it

survives until someone destroys it

explicitly using the delete directive.

• This could lead to memory leaks

– if the programmer forgets to delete

objects no longer needed, they remain

on the heap as wasted space

Methods (Java)public class CoffeeMaker

public void prepareCoffee() <>

public void prepareCoffeeSweet(int sugarAm)<>

aCoffeeMaker = new CoffeeMaker();

Methods (Java)public class CoffeeMaker

public void prepareCoffee() <>

public void prepareCoffeeSweet(int sugarAm)<>

aCoffeeMaker = new CoffeeMaker();

Methods (C++)class CoffeeMaker

void prepareCoffeeSweet(int sugarAm)<>

aPtrCoffeeMaker = new CoffeeMaker;

Methods (C++)class CoffeeMaker

void prepareCoffeeSweet(int sugarAm)<>

aPtrCoffeeMaker = new CoffeeMaker;

• (.pdf) Garbage Collection: Automatic Memory Management in the

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Java Memory Management, published by Packt

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README.md

This is the code repository for Java Memory Management, published by Packt.

A comprehensive guide to garbage collection and JVM tuning

Understanding how Java organizes memory is important for every Java professional, but this particular topic is a common knowledge gap for many software professionals. Having in-depth knowledge of memory functioning and management is incredibly useful in writing and analyzing code, as well as debugging memory problems. In fact, it can be just the knowledge you need to level up your skills and career.

This book covers the following exciting features:

• Understand the schematics of debugging and how to design the application to perform well
• Discover how garbage collectors work
• Distinguish between various garbage collector implementations
• Identify the metrics required for analyzing application performance
• Configure and monitor JVM memory management
• Identify and solve memory leaks

If you feel this book is for you, get your copy today!

Instructions and Navigations

All of the code is organized into folders. For example, Chapter04.

The code will look like the following:

Object o = new Object(); System.out.println(o); o = null; 

Following is what you need for this book: This book is for all levels of Java professionals, regardless of whether you’re a junior or senior developer, a DevOps engineer, a tester, or the system admin of a Java application. If you currently don’t have in-depth knowledge of Java memory, garbage collection, and/or JVM tuning, then this book will help you to take your Java skills to the next level.

With the following software and hardware list you can run all code files present in the book (Chapter 1-7).

Software and Hardware List

We also provide a PDF file that has color images of the screenshots/diagrams used in this book. Click here to download it.

• Domain-Driven Design with Java — A Practitioner’s Guide [Packt][Amazon]
• Learn Java 17 Programming — Second Edition [Packt][Amazon]

Maaike van Putten is an experienced software developer and trainer with a passion for software development and helping others to get to the next level in their career. Some of her favorite languages are Java, JavaScript, and Python. She participates as a developer in software development projects and teaches a lot of training courses, ranging from IT for beginners to advanced topics for senior software developers. She also loves to create online content to help a larger audience, and she does so for diverse platforms such as Pluralsight, LinkedIn Learning, and Udemy.

Seán Kennedy is a university lecturer with over 20 years of experience in teaching. He has a PhD in IT and is Oracle-certified in Java at the Professional level (OCP). In his daily work, he teaches Java on a bespoke master’s program for a highly regarded software company. He has a YouTube channel called Let’s Get Certified that teaches Java at all levels and prepares candidates for Java certification. He also has similar courses on Udemy. Outside of work, he enjoys tennis, walking, nature, reading, and TV.

If you have already purchased a print or Kindle version of this book, you can get a DRM-free PDF version at no cost.
Simply click on the link to claim your free PDF.

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Memory Management for Real-Time Java: An Efficient Solution using Hardware Support*

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Proceedings of the 5th international workshop on Java technologies for real-time and embedded systems — JTRES ’07

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We present a method to analyze, monitor and control dynamic memory allocation in Java. It first consists in performing pointer and escape analysis to detect memory scopes. This information is used to automatically instrument Java programs in such a way memory is allocated and freed by a region-based memory manager. Our source code instrumentation fully exploits the result of scope analysis by dynamically mapping allocation places to the region stack at runtime via a registering mechanism.

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Proceedings of the 6th international workshop on Java technologies for real-time and embedded systems — JTRES ’08

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Abstract The region-based memory model of The Realtime Specification for Java (RTSJ) is quite rigid, and it complicates the development of reusable predictable software for large-scale systems. In this paper, we propose an extension to the region model of the RTSJ called AGCMemory (Acyclic Garbage Collected Memory). This extension enables the transparent destruction of floating garbage created during the execution of Java methods.

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ACM Transactions on Embedded Computing Systems

Источник

Java Memory Management: A comprehensive guide to garbage collection and JVM tuning

Understanding how Java organizes memory is important for every Java professional, but this particular topic is a common knowledge gap for many software professionals. Having in-depth knowledge of memory functioning and management is incredibly useful in writing and analyzing code, as well as debugging memory problems. In fact, it can be just the knowledge you need to level up your skills and career.

In this book, you’ll start by working through the basics of Java memory. After that, you’ll dive into the different segments individually. You’ll explore the stack, the heap, and the Metaspace. Next, you’ll be ready to delve into JVM standard garbage collectors. The book will also show you how to tune, monitor and profile JVM memory management. Later chapters will guide you on how to avoid and spot memory leaks.

By the end of this book, you’ll have understood how Java manages memory and how to customize it for the benefit of your applications.

• Understand the schematics of debugging and how to design the application to perform well
• Discover how garbage collectors work
• Distinguish between various garbage collector implementations
• Identify the metrics required for analyzing application performance
• Configure and monitor JVM memory management
• Identify and solve memory leaks

Resolve the captcha to access the links!

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