What is Garbage Collection in Java

💡 Concept: Garbage Collection in Java

Garbage Collection (GC) in Java is an automatic memory management process that identifies and frees up memory occupied by objects no longer in use.

📘 Quick Intro

GC helps prevent memory leaks and optimizes memory usage by reclaiming unused objects during runtime.

🧠 Analogy

Think of garbage collection as a janitor cleaning unused files and trash to free up space, so the system stays tidy and efficient.

🔧 Technical Explanation

GC runs on the JVM and manages heap memory automatically.
Detects unreachable objects by tracing references.
Common algorithms: Mark-and-Sweep, Generational GC.
Generational GC divides heap into young and old generations.
Helps improve application performance by reclaiming unused memory.

🎯 Use Cases

✅ Automatic memory management in Java applications.
✅ Preventing memory leaks and out-of-memory errors.
✅ Optimizing long-running server applications.

💻 Example: Suggesting Garbage Collection


public class GCDemo {
    public static void main(String[] args) {
        GCDemo obj = new GCDemo();
        obj = null; // Eligible for GC
        System.gc(); // Request JVM to run GC
        System.out.println("GC requested");
    }
}

❓ Interview Q&A

Q1: What is garbage collection?
A: Automatic memory management in Java.

Q2: How does GC identify unused objects?
A: By tracing object references.

Q3: What are common GC algorithms?
A: Mark-and-Sweep, Generational GC.

Q4: Can you force garbage collection?
A: You can request it using System.gc(), but JVM decides when to run.

Q5: What is generational GC?
A: Heap divided into young and old generations for efficiency.

Q6: Does GC guarantee immediate memory reclaim?
A: No, it is up to JVM scheduling.

Q7: Can GC cause performance overhead?
A: Yes, during GC cycles.

Q8: What is memory leak in Java?
A: When unreachable objects are not garbage collected.

Q9: Is GC automatic in Java?
A: Yes, managed by JVM.

Q10: How to optimize GC?
A: By tuning JVM and managing object lifecycles properly.

📝 MCQs

Q1. What is garbage collection in Java?

Manual memory management
Automatic memory management
Garbage creation
None

Q2. How does GC identify unused objects?

Counting references
Tracing references
Random
Manual marking

Q3. What are common GC algorithms?

Mark-and-Sweep, Generational
Reference counting
Copying
None

Q4. Can you force garbage collection?

Yes
No, only request
Always
Sometimes

Q5. What is generational GC?

Heap merged
Heap divided for efficiency
Stack only
None

Q6. Does GC guarantee immediate reclaim?

Yes
No
Sometimes
Always

Q7. Can GC cause overhead?

No
Yes
Maybe
Never

Q8. What is memory leak?

Unused memory
Unreachable objects not collected
Garbage data
None

Q9. Is GC automatic?

Yes
No
Sometimes
Never

Q10. How to optimize GC?

Ignore
Tune JVM and object lifecycle
Increase memory
None

💡 Bonus Insight

Effective garbage collection management is crucial for performance in large-scale Java applications.

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