1️⃣ Use the Right Garbage Collector for Your Application
Different GC algorithms are optimized for different workloads:
| GC Type | Best For | Enable With |
|---|---|---|
| G1GC (Garbage First) | Balanced performance for large heaps (default from Java 9) | -XX:+UseG1GC |
| ZGC (Ultra-Low Latency) | Large applications with minimal GC pauses | -XX:+UseZGC |
| Shenandoah GC | Low-latency applications with concurrent compaction | -XX:+UseShenandoahGC |
| Parallel GC | High-throughput applications (batch processing) | -XX:+UseParallelGC |
| Serial GC | Small applications, single-threaded workloads | -XX:+UseSerialGC |
📌 Best Practice: For most modern applications, G1GC or ZGC is recommended to minimize GC pauses.
2️⃣ Optimize Object Allocation and Avoid Unnecessary Object Creation
Creating too many short-lived objects increases the frequency of Minor GCs in the Young Generation.
How to Reduce Object Creation:
✔ Use primitive types instead of wrapper classes (e.g., int instead of Integer).
✔ Reuse immutable objects (e.g., use StringBuilder instead of String for concatenation).
✔ Avoid unnecessary autoboxing/unboxing, which creates temporary objects.
✔ Pool reusable objects (e.g., use ThreadLocal, connection pools).
Example: Avoiding Unnecessary Object Creation
❌ Bad: Creates a new object every loop iteration
for (int i = 0; i < 1000; i++) {
String result = new String("Hello" + i);
}
✅ Good: Uses a StringBuilder to minimize allocations
StringBuilder sb = new StringBuilder();
for (int i = 0; i < 1000; i++) {
sb.append("Hello").append(i);
}
String result = sb.toString();
📌 Best Practice: Reduce short-lived object creation to decrease GC pressure.
3️⃣ Tune JVM Heap Size and GC Settings
Setting the correct heap size helps prevent frequent Full GC and OutOfMemoryErrors.
Key JVM Heap Size Options
| Option | Description |
|---|---|
-Xms512m | Initial heap size (e.g., 512MB) |
-Xmx4g | Maximum heap size (e.g., 4GB) |
-XX:NewRatio=3 | Ratio of Young to Old Generation |
-XX:SurvivorRatio=8 | Eden to Survivor space ratio |
📌 Best Practice: Set heap size according to workload and monitor usage.
4️⃣ Use Efficient Data Structures
Choosing the right data structures reduces memory footprint and improves performance.
Best Practices for Data Structures
✔ Use ArrayList instead of LinkedList for faster iteration and lower GC overhead.
✔ Use EnumSet instead of HashSet for storing small sets of enums.
✔ Use ConcurrentHashMap instead of synchronized HashMap to reduce memory contention.
✔ Use WeakHashMap or WeakReference for caches to allow GC to reclaim unused objects.
Example: Using WeakHashMap for Caching
import java.util.WeakHashMap;
public class CacheExample {
public static void main(String[] args) {
WeakHashMap<Object, String> cache = new WeakHashMap<>();
Object key = new Object();
cache.put(key, "Cached Data");
key = null; // Remove strong reference
System.gc(); // Suggest GC
System.out.println("Cache size: " + cache.size()); // May be 0 if GC ran
}
}
📌 Best Practice: Choose lightweight and efficient data structures to reduce memory overhead.
5️⃣ Reduce Memory Retention by Clearing Unused References
Holding unnecessary references prevents GC from reclaiming memory.
How to Reduce Memory Retention
✔ Set objects to null when they are no longer needed.
✔ Use WeakReference or SoftReference for objects that can be discarded.
✔ Manually clear large collections (e.g., List.clear() instead of list = new ArrayList<>();).
✔ Use try-with-resources (AutoCloseable) for file, DB, and socket operations.
Example: Explicitly Clearing Unused References
public class MemoryManagementExample {
public static void main(String[] args) {
List<Integer> list = new ArrayList<>(1000000);
for (int i = 0; i < 1000000; i++) {
list.add(i);
}
list.clear(); // Helps GC reclaim memory
System.gc(); // Suggest GC
}
}
6️⃣ Avoid Memory Leaks
Memory leaks occur when objects are no longer used but still referenced, preventing GC from reclaiming them.
Common Causes of Memory Leaks and How to Fix Them
| Cause | Fix |
|---|---|
| Static collections holding objects | Use WeakHashMap instead of HashMap. |
| Listeners and callbacks not removed | Unregister listeners when done. |
| ThreadLocal variables accumulating objects | Call ThreadLocal.remove() after use. |
| Long-lived references in caches | Use SoftReference or WeakReference. |
📌 Best Practice: Regularly monitor memory usage and fix memory leaks.
7️⃣ Monitor GC Performance
Use tools to analyze memory usage and optimize GC behavior.
Useful Tools for Monitoring GC
jstat– Monitor GC statistics (jstat -gc <pid>).- VisualVM – Graphical analysis of heap usage.
- JConsole – Monitor GC activity in real time.
- Eclipse MAT (Memory Analyzer Tool) – Detect memory leaks.
📌 Best Practice: Analyze memory behavior using profiling tools to prevent excessive GC overhead.
8️⃣ Use Object Pools for Expensive Objects
Objects that are expensive to create and frequently reused should be pooled instead of reallocated.
Example: Using Object Pooling
import java.util.concurrent.ArrayBlockingQueue;
public class ObjectPool {
private final ArrayBlockingQueue<MyObject> pool = new ArrayBlockingQueue<>(10);
public MyObject borrowObject() {
return pool.poll(); // Get object or return null
}
public void returnObject(MyObject obj) {
pool.offer(obj); // Reuse object
}
}
📌 Best Practice: Use object pooling for heavy objects like database connections, threads, and network sockets.
9️⃣ Minimize System.gc() Calls
Calling System.gc() forces a Full GC, stopping all application threads.
🚫 Avoid:
System.gc(); // Causes performance drop
📌 Best Practice: Let the JVM decide when to run GC.
🔟 Summary: Key Best Practices
✔ Choose the right GC algorithm (G1GC, ZGC).
✔ Reduce object creation (use primitive types, avoid unnecessary allocations).
✔ Tune JVM heap size (-Xms, -Xmx) based on application needs.
✔ Use efficient data structures (ArrayList, WeakHashMap).
✔ Clear unused references (null, WeakReference).
✔ Avoid memory leaks (remove listeners, clear collections).
✔ Monitor memory usage with profiling tools (jstat, VisualVM).
✔ Use object pooling for frequently used heavy objects.
✔ Minimize System.gc() calls to prevent performance issues.
🚀 By following these best practices, you can reduce GC impact and improve Java application performance! 🚀