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JVM

Memory areas, garbage collection, JIT, class loading, tuning.

25 questions
Memory AreasGarbage CollectionGC TuningJITClass LoadingTroubleshooting

Sample Questions (25 live)

Memory AreasEasy

JVM vs JRE vs JDK — what's the difference, and which do you ship in a Docker image?

InfosysTCSCognizantRead →
Memory AreasEasy

How does Java achieve 'write once, run anywhere' via bytecode?

TCSInfosysWiproRead →
Memory AreasEasy

What are the main JVM memory areas, and which are shared vs per-thread?

InfosysCognizantAccentureRead →
Memory AreasEasy

Stack vs Heap — where do primitives, references and objects actually live?

TCSInfosysDeloitteRead →
Garbage CollectionMedium

Why is the heap split into young and old generations, and what's a minor vs major GC?

AmazonMicrosoftDeloitteRead →
Garbage CollectionMedium

How does garbage collection decide what to free — and what are GC roots?

AmazonGoogleMicrosoftRead →
Memory AreasMedium

What replaced PermGen with Metaspace, and how can you still get a Metaspace OOM?

AmazonDeloitteCognizantRead →
GC TuningMedium

How do you size the heap (-Xms/-Xmx), and what's special about JVMs in containers?

AmazonMicrosoftDeloitteRead →
GC TuningMedium

How do you choose a garbage collector — Serial, Parallel, G1, ZGC or Shenandoah?

AmazonGoogleMicrosoftRead →
GC TuningMedium

What is a stop-the-world pause, and how do you reduce GC pause times?

AmazonMicrosoftGoogleRead →
TroubleshootingMedium

What are the different OutOfMemoryError types, and what does each tell you?

AmazonMicrosoftDeloitteRead →
TroubleshootingMedium

How do you enable and read GC logs to diagnose a memory problem?

AmazonDeloitteGoogleRead →
Garbage CollectionMedium

Strong, weak, soft and phantom references — when do you use each?

AmazonGoogleMicrosoftRead →
JITMedium

How does JIT compilation work (C1/C2, tiered), and why is JVM warm-up a thing?

AmazonGoogleMicrosoftRead →
Garbage CollectionHard

How does G1 GC work internally — regions, mixed collections and humongous objects?

AmazonGoogleMicrosoftRead →
Garbage CollectionHard

How do ZGC and Shenandoah achieve sub-millisecond pauses on huge heaps?

GoogleAmazonMicrosoftRead →
JITHard

What is escape analysis, and how does it let the JVM allocate objects on the stack?

GoogleAmazonMicrosoftRead →
TroubleshootingHard

Walk me through diagnosing long GC pauses / high GC CPU in production.

AmazonGoogleMicrosoftRead →
TroubleshootingHard

What is off-heap / direct memory, and how do you track and bound it?

AmazonGoogleMicrosoftRead →
Class LoadingHard

How does the class loading delegation model work, and why do enterprise apps customize it?

AmazonMicrosoftDeloitteRead →
TroubleshootingMedium

How does Class-Data Sharing (CDS/AppCDS) cut JVM startup time, and why does it matter for containers and serverless?

AmazonGoogleRead →
JITHard

GraalVM Native Image vs a jlink'd JVM runtime — what do you actually give up for instant startup?

AmazonGoogleOracleRead →
JITHard

Why does timing a loop with System.currentTimeMillis() lie to you, and how does JMH avoid those traps?

AmazonGoogleOracleRead →
TroubleshootingHard

A Java service is pegging CPU with no errors logged — how do you find out why?

AmazonMicrosoftGoogleRead →
TroubleshootingMedium

How can a Stream or lambda closure quietly leak memory in a long-lived cache?

AmazonMicrosoftRead →

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