♻️ Advance Java — Garbage Collection

? Quick Overview

Garbage Collection (GC) in Java is an automatic memory management process. The JVM continuously identifies unused objects and reclaims memory to prevent leaks and improve performance. In Advanced Java, understanding GC behavior is critical for building scalable and high-performance applications.

? Key Concepts

• Automatic memory management by JVM
• Objects become eligible for GC, not explicitly deleted
• Heap memory divided into generations
• GC runs in background using different algorithms

? Syntax & Theory

Java uses a generational heap model:

• Young Generation — New objects (Eden, Survivor spaces)
• Old Generation — Long-living objects
• Metaspace — Class metadata (Java 8+)

An object becomes eligible for garbage collection when no active references point to it. The System.gc() call is only a request, not a guarantee.

? Code Example — Object Eligibility

// Demonstrates object eligibility for garbage collection
class DemoGC {
public static void main(String[] args) {
DemoGC obj1 = new DemoGC();
DemoGC obj2 = new DemoGC();

obj1 = null;
obj2 = null;

System.gc();
}
}

? Live Output / Explanation

? Code Example — finalize() Method

// Shows finalize method being called before object destruction
class TestGC {
protected void finalize() {
System.out.println("Object collected by GC");
}

public static void main(String[] args) {
TestGC t = new TestGC();
t = null;
System.gc();
}
}