Book Image

Java Memory Management

By : Maaike van Putten, Dr. Seán Kennedy
Book Image

Java Memory Management

By: Maaike van Putten, Dr. Seán Kennedy

Overview of this book

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.

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Table of Contents (10 chapters)
Preface
Preface
Who this book is for
What this book covers
To get the most out of this book
Download the example code files
Download the color images
Conventions used
Get in touch
Share Your Thoughts
Download a Free PDF copy of this book
1
Chapter 1: Different Parts of the Java Memory
Chapter 1: Different Parts of the Java Memory
Technical requirements
Understanding computer memory and Java memory
Creating variables in Java
Storing variables on the stack
Creating objects in Java
Storing objects on the heap
Exploring the Metaspace
Summary
Free Chapter
2
Chapter 2: Primitives and Objects in Java Memory
Chapter 2: Primitives and Objects in Java Memory
Technical requirements
Understanding primitives on the stack and heap
Storing objects on the heap
Managing object references and security
Summary
3
Chapter 3: Zooming in on the Heap Space
Chapter 3: Zooming in on the Heap Space
Exploring the different generations on the heap
Learning how the spaces are used
Summary
4
Chapter 4: Freeing Memory with Garbage Collection
Chapter 4: Freeing Memory with Garbage Collection
Technical requirements
Being eligible for GC
Marking by the garbage collector
Sweeping by the garbage collector
Exploring GC implementations
Monitoring GC
Summary
5
Chapter 5: Zooming in on the Metaspace
Chapter 5: Zooming in on the Metaspace
JVM usage of the Metaspace
Class loading
Releasing Metaspace memory
Summary
6
Chapter 6: Configuring and Monitoring the Memory Management of the JVM
Chapter 6: Configuring and Monitoring the Memory Management of the JVM
Technical requirements
The basics of JVM tuning for memory management
Obtaining relevant metrics for memory management
Profiling Java applications
Tuning the configurations of the JVM
7
Chapter 7: Avoiding Memory Leaks
Chapter 7: Avoiding Memory Leaks
Technical requirements
Understanding memory leaks
Spotting memory leaks
Avoiding memory leaks
Summary
8
Index
Index
Why subscribe?
9
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Other Books You May Enjoy
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Marking by the garbage collector

Marking marks any live objects and anything not marked as ready to be garbage collected. The objects keep a special bit that determines whether they are marked or not. Upon creation, the bit is 0. In the mark phase, if an object is still in use and should not be removed, it gets set to 1.

The heap is constantly changing and so is the stack. Objects on the heap that do not have a connection to the step are eligible for GC. They are unreachable and there is no possible way for the application to be using these objects. The objects that are not ready for removal are marked; the unmarked objects will be removed.

How exactly this is implemented differs depending on the implementation of Java and the specific garbage collector you are using. But at a high level, this process starts from the stack. All the object references on the stack are followed and the objects are marked.

If we look at our previous example, this is how they would be marked. We...

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