What are strong and weak references?

Q: What is a strong reference?

A reference that prevents the object from being collected by the garbage collector.

Q: What is a weak reference?

A reference that allows the object to be collected if no strong references exist.

💡 Concept: Strong and Weak References

Strong references keep objects alive and prevent garbage collection, whereas weak references allow objects to be collected if no strong references exist.

📘 Quick Intro

Strong references are default references in C#. Weak references enable conditional object lifetime, useful for caching and memory optimization.

🧠 Analogy

Think of a strong reference as a firm grip on an object, ensuring it stays, while a weak reference is a loose grip that lets go when needed.

🔧 Technical Explanation

🛡️ Strong references prevent garbage collector from collecting the object.
👻 Weak references do not prevent collection and can be checked for object availability.
🔄 Useful for caches, where you want to keep objects if memory allows.
⚙️ Implemented in C# via WeakReference class.
🔍 Accessing a weak reference requires checking if target is still alive.

🎯 Use Cases

✅ Implementing memory-sensitive caches.
✅ Avoiding memory leaks due to lingering references.
✅ Enabling objects to be collected when not strongly needed.
✅ Improving application memory efficiency.

💻 Code Example


var strongRef = new Object(); // Strong reference

var weakRef = new WeakReference(strongRef); // Weak reference to the same object

strongRef = null; // Remove strong reference

if (weakRef.IsAlive) {
    var obj = weakRef.Target;
    // Use obj if not null
}

❓ Interview Q&A

Q1: What is a strong reference?
A: A reference that keeps an object alive.

Q2: What is a weak reference?
A: A reference that allows GC to collect the object.

Q3: When are weak references useful?
A: For memory-sensitive caches.

Q4: How to create a weak reference?
A: Using the WeakReference class.

Q5: Can you access a weak reference safely?
A: Yes, by checking if it is alive first.

Q6: Do weak references prevent memory leaks?
A: They help by not prolonging object lifetime.

Q7: Are strong references default?
A: Yes, all references are strong unless weak reference is used.

Q8: Can weak references cause problems?
A: Yes, if not checked before use.

Q9: What happens if weak reference target is collected?
A: Target becomes null.

Q10: Are weak references supported in all .NET versions?
A: Yes, from early versions onwards.

📝 MCQs

Q1. What does a strong reference do?

Allows GC
Keeps object alive
Deletes object
Copies object

Q2. What is a weak reference?

Prevents GC
Allows GC collection
Throws exceptions
Creates leaks

Q3. When to use weak references?

Always
Memory-sensitive caching
Never
Debugging

Q4. How to create a weak reference?

StrongReference
WeakReference
GarbageCollector
ObjectReference

Q5. Can weak reference be null?

No
Yes if collected
Never
Sometimes

Q6. Are strong references default?

No
Yes
Sometimes
Only in unsafe code

Q7. Do weak references prevent leaks?

Cause leaks
Help prevent leaks
No effect
Increase memory

Q8. What if weak reference target is collected?

Throws error
Target is null
GC stops
Program crashes

Q9. Are weak references in all .NET?

No
Yes
Only .NET Core
Only .NET Framework

Q10. Can weak references cause problems?

No
Yes if unchecked
Always
Rarely

💡 Bonus Insight

Using weak references thoughtfully can optimize memory usage and avoid unintended object retention.

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