[{"_1":2,"_3":-5,"_4":-5},"loaderData",{"_5":6},"actionData","errors","routes/blog-tag",{"_7":8,"_9":10},"tag",{"_31":89,"_73":90,"_35":91},"articles",{"_11":12,"_13":14,"_15":16,"_17":16,"_18":19,"_20":21,"_22":23,"_24":23,"_25":16,"_26":27},"content",[30],"pageable",{"_28":21,"_29":19},"totalElements",1,"totalPages","size",10,"number",0,"first",true,"last","numberOfElements","empty",false,"page_number","page_size",{"_31":32,"_33":34,"_35":36,"_37":38,"_11":39,"_40":-5,"_41":23,"_42":27,"_43":44,"_45":46,"_47":48,"_49":50,"_51":52,"_53":52,"_54":55,"_56":57,"_58":59,"_60":52,"_61":62,"_63":64,"_65":66,"_67":68,"_69":70,"_71":72},"id",89,"title","Garbage Collection","slug","dsa-cheatsheet-part-18-gc","excerpt","Visual guide to JVM Garbage Collection: generational GC, Eden/Survivor/Old spaces. Watch objects move through generations.","# Garbage Collection\n\n## 📋 Quick Reference\n\n| Property | Value |\n|----------|-------|\n| **Purpose** | Automatic memory management |\n| **Key Concept** | Identify and reclaim unreachable objects |\n| **Generations** | Young (Eden + Survivors), Old (Tenured), Metaspace |\n| **Common GCs** | G1 (default), ZGC, Shenandoah, Parallel, Serial |\n| **Best For** | Understanding memory behavior, tuning performance |\n\n**One-liner**: *Automatic memory management that identifies and reclaims unreachable objects across generational heap regions.*\n\n---\n\n## 🎮 Interactive Visualizer\n\nWatch how the garbage collector manages memory:\n\n```visualizer-gc\nshowControls: true\nshowCode: true\n```\n\n**Try these operations:**\n1. Create objects - see them allocated in Eden\n2. Trigger Minor GC - watch survivors age\n3. Fill Old Gen - observe Major GC\n4. See object promotion from Young to Old\n\n---\n\n## 🔧 Memory Structure\n\n### Generational Heap\n\n```\n┌──────────────────────────────────────────────────────┐\n│ JVM Heap │\n├───────────────────────────┬──────────────────────────┤\n│ Young Generation │ Old Generation │\n├─────────┬────────┬────────┤ │\n│ Eden │ S0 │ S1 │ Tenured │\n│ │(From) │(To) │ │\n├─────────┴────────┴────────┴──────────────────────────┤\n│ Metaspace │\n└──────────────────────────────────────────────────────┘\n\nEden: New objects allocated here\nS0/S1 (Survivors): Objects that survived GC\nTenured: Long-lived objects\nMetaspace: Class metadata (not part of heap, uses native memory)\n```\n\n### Object Lifecycle\n\n```\n1. Allocation: new Object() → Eden space\n2. Minor GC: Live objects → Survivor space\n3. Aging: Objects survive multiple GCs → age++\n4. Promotion: Age threshold reached → Old generation\n5. Major GC: Old generation collected (slower)\n```\n\n---\n\n## 📊 GC Types and Algorithms\n\n### Minor GC (Young Gen)\n\n```java\n// Triggers when Eden fills up\n// Collects Young Generation only\n// Uses copying collector\n// Typically milliseconds\n\n// Objects copied: Eden → Survivor (or Old if aged)\n// Dead objects: Reclaimed\n```\n\n### Major/Full GC (All Generations)\n\n```java\n// Triggers when Old Gen fills up\n// Collects entire heap\n// May cause noticeable pause\n// Typically tens of milliseconds to seconds\n```\n\n### Common Collectors\n\n| Collector | Focus | Pause Time | Throughput |\n|-----------|-------|------------|------------|\n| Serial | Simplicity | Long | Low |\n| Parallel | Throughput | Medium | High |\n| G1 (default) | Balance | Predictable | Good |\n| ZGC | Low latency | <10ms | Good |\n| Shenandoah | Low latency | <10ms | Good |\n\n---\n\n## ✅ GC Tuning Basics\n\n### JVM Flags\n\n```bash\n# Heap size\n-Xms2g -Xmx4g # Initial and max heap\n\n# GC selection\n-XX:+UseG1GC # G1 (default in Java 9+)\n-XX:+UseZGC # ZGC (low latency)\n-XX:+UseShenandoahGC # Shenandoah\n\n# G1 tuning\n-XX:MaxGCPauseMillis=200 # Target pause time\n-XX:G1HeapRegionSize=16m # Region size\n\n# Logging\n-Xlog:gc*:file=gc.log # GC logs (Java 9+)\n```\n\n### Monitoring\n\n```java\n// Programmatic access\nRuntime runtime = Runtime.getRuntime();\nlong totalMemory = runtime.totalMemory();\nlong freeMemory = runtime.freeMemory();\nlong maxMemory = runtime.maxMemory();\n\n// Suggest GC (not guaranteed)\nSystem.gc();\n\n// Get garbage collector beans\nList gcBeans =\n ManagementFactory.getGarbageCollectorMXBeans();\nfor (GarbageCollectorMXBean gc : gcBeans) {\n System.out.println(gc.getName() + \": \" + gc.getCollectionCount());\n}\n```\n\n---\n\n## 🧩 Common Memory Issues\n\n### Memory Leak\n\n```java\n// ❌ Objects never become unreachable\nstatic List