book

Java Memory Management

by Maaike van Putten, Dr. Seán Kennedy

November 2022

Intermediate to advanced

146 pages

3h 16m

English

Packt Publishing

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Who this book is forWhat this book coversTo get the most out of this bookDownload the example code filesDownload the color imagesConventions usedGet in touchShare Your ThoughtsDownload a Free PDF copy of this book
Technical requirementsUnderstanding computer memory and Java memoryComputer memoryAccessing the main memoryOverview of the main memoryJava memory and the JVMThe JVMMemory management and the JVMMemory management before JavaUnderstanding the JVM’s components for memory managementRuntime data areaCreating variables in JavaPrimitives and reference typesStoring variables on the stackCurrent frame and current methodElements of the frameValues on the stackPrimitives and wrapper classesCreating objects in JavaStoring objects on the heapExploring the MetaspaceSummary
Technical requirementsUnderstanding primitives on the stack and heapStoring objects on the heapReferencesObjectsUnderstanding the differences between references and objectsManaging object references and securityInspecting the escaping references issueSummary
Exploring the different generations on the heapGarbage collection rootsLearning how the spaces are usedUnderstanding the minor garbage collection algorithmDemonstrating the minor garbage collection algorithm in actionSummary
Technical requirementsBeing eligible for GCMarking by the garbage collectorStop-the-worldReference counting and islands of isolationSweeping by the garbage collectorNormal sweepingSweeping with compactingSweeping with copyingExploring GC implementationsGenerational GCSerial GCParallel GCCMS GCG1 GCZ GCMonitoring GCSummary
JVM usage of the MetaspaceClass loadingReleasing Metaspace memoryMetaspace runs out of memoryMetaspace size exceeds a JVM-set thresholdGarbage collection of the MetaspaceSummary
Technical requirementsThe basics of JVM tuning for memory managementObtaining relevant metrics for memory managementWell-functioning memoryNormal latencyLevel of throughputProfiling Java applicationsProfiling with jstat and jmapProfiling with VisualVMTuning the configurations of the JVMTuning the heap size and thread stack sizeLogging low memoryTuning the MetaspaceGarbage collection tuning
Technical requirementsUnderstanding memory leaksSpotting memory leaksHeap memory footprintGarbage collector activityHeap dumpAvoiding memory leaksCommon pitfalls and how to avoid themSummary

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Content preview from Java Memory Management

2 Primitives and Objects in Java Memory

In Chapter 1, we saw the differences between primitives, objects, and references. We learned that primitives are types that come with the Java language; in other words, we do not have to define primitive types, we just use them. For example, int x; defines (creates) a primitive variable, x, which is of (the primitive) type int. This means that x can store whole integer numbers only, for example, -5, 0, 12, and so on.

We also learned that objects are instantiations of a class and that we use the new keyword to create instances of objects. For example, assuming a Person class exists, new Person(); instantiates (creates) an object of type Person. This object will be stored on the heap.

We saw that references ...