Garbage Collection

📋 Quick Reference

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🎮 Interactive Visualizer

Watch how the garbage collector manages memory:

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1. Create objects - see them allocated in Eden
2. Trigger Minor GC - watch survivors age
3. Fill Old Gen - observe Major GC
4. See object promotion from Young to Old

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🔧 Memory Structure

Generational Heap

┌──────────────────────────────────────────────────────┐
│                        JVM Heap                       │
├───────────────────────────┬──────────────────────────┤
│      Young Generation     │     Old Generation       │
├─────────┬────────┬────────┤                          │
│  Eden   │ S0     │ S1     │      Tenured             │
│         │(From)  │(To)    │                          │
├─────────┴────────┴────────┴──────────────────────────┤
│                    Metaspace                          │
└──────────────────────────────────────────────────────┘

Eden: New objects allocated here
S0/S1 (Survivors): Objects that survived GC
Tenured: Long-lived objects
Metaspace: Class metadata (not part of heap, uses native memory)

Object Lifecycle

1. Allocation: new Object() → Eden space
2. Minor GC: Live objects → Survivor space
3. Aging: Objects survive multiple GCs → age++
4. Promotion: Age threshold reached → Old generation
5. Major GC: Old generation collected (slower)

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📊 GC Types and Algorithms

Minor GC (Young Gen)

JAVA(7 lines)
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Major/Full GC (All Generations)

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Common Collectors

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✅ GC Tuning Basics

JVM Flags

BASH(14 lines)
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Monitoring

JAVA(15 lines)
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🧩 Common Memory Issues

Memory Leak

JAVA(9 lines)
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OutOfMemoryError

JAVA(13 lines)
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GC Thrashing

JAVA(6 lines)
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🔄 Reference Types

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WeakHashMap Example

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⚠️ Common Pitfalls

1. Relying on Finalize

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2. Calling System.gc()

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3. Premature Optimization

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4. Static Collections Growing Forever

JAVA(11 lines)
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🎯 Interview Practice

Test your GC knowledge with 10 curated interview questions:

🎤 Garbage Collection Interview Mode - Coming Soon

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🎤 Interview Tips

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Java uses generational GC. New objects go to Eden. Minor GC copies survivors to Survivor spaces, aging them. After surviving multiple GCs, objects are promoted to Old Gen. Major GC collects Old Gen when full.

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Minor GC collects Young Generation only - fast and frequent. Major/Full GC collects the entire heap including Old Gen - slower and less frequent. Minor uses copying; Major may use mark-sweep-compact.

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Use heap dumps (jmap), profilers (VisualVM, JFR), and GC logs. Look for growing Old Gen despite GC, objects accumulating over time, or specific classes with unexpectedly high instance counts.

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GC timing is a JVM implementation detail. The JVM optimizes for overall performance, not immediate cleanup. Forcing immediate GC would hurt throughput and is rarely what you actually need.

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📚 Series Navigation

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