What is reflection and how is it used

💡 Concept: Java Reflection

Reflection in Java is a powerful API that allows a program to inspect and manipulate classes, methods, and fields at runtime.

📘 Quick Intro

Using reflection, you can examine class metadata, invoke methods dynamically, and access private members, facilitating dynamic behavior.

🧠 Analogy

Reflection is like having X-ray vision to see inside a compiled class and interact with its components dynamically.

🔧 Technical Explanation

Reflection API includes classes like Class, Method, Field, and Constructor.
Allows dynamic loading and inspection of classes.
Can invoke methods and access fields at runtime.
Used for frameworks, serialization, and debugging tools.
Can bypass access modifiers using setAccessible(true).

🎯 Use Cases

✅ Developing frameworks and libraries that require dynamic behavior.
✅ Inspecting classes during runtime for debugging or testing.
✅ Serialization/deserialization and ORM frameworks.

💻 Example: Using Reflection to Invoke a Method


import java.lang.reflect.Method;

public class ReflectionDemo {
    public void sayHello() {
        System.out.println("Hello from Reflection!");
    }

    public static void main(String[] args) throws Exception {
        ReflectionDemo obj = new ReflectionDemo();
        Method method = obj.getClass().getMethod("sayHello");
        method.invoke(obj);
    }
}

❓ Interview Q&A

Q1: What is reflection in Java?
A: API for inspecting and manipulating classes at runtime.

Q2: Which classes are used in reflection?
A: Class, Method, Field, Constructor.

Q3: Can reflection access private fields?
A: Yes, with setAccessible(true).

Q4: What are common uses of reflection?
A: Frameworks, serialization, debugging.

Q5: Is reflection performance costly?
A: Yes, compared to direct calls.

Q6: Can reflection break encapsulation?
A: Potentially, if misused.

Q7: Is reflection type-safe?
A: No, it bypasses compile-time checks.

Q8: How to get class object for reflection?
A: Using Class.forName() or obj.getClass().

Q9: Can reflection create objects?
A: Yes, via Constructor class.

Q10: What are the risks of reflection?
A: Security and performance impacts.

📝 MCQs

Q1. What is reflection in Java?

Compile time checking
API for runtime inspection
Memory management
Thread management

Q2. Which classes are used in reflection?

Thread, Process
Class, Method, Field, Constructor
Scanner, File
Socket, Stream

Q3. Can reflection access private fields?

No
Yes
Sometimes
Never

Q4. What are common uses of reflection?

I/O
Frameworks and debugging
Networking
Database

Q5. Is reflection performance costly?

No
Yes
Depends
Unknown

Q6. Can reflection break encapsulation?

No
Yes
Maybe
Never

Q7. Is reflection type-safe?

Yes
No
Sometimes
Never

Q8. How to get class object for reflection?

new Class()
Class.forName()
Class.get()
Class.load()

Q9. Can reflection create objects?

No
Yes
Sometimes
Never

Q10. What are risks of reflection?

None
Security and performance impacts
Only security
Only performance

💡 Bonus Insight

Reflection is essential for building dynamic and flexible Java frameworks but should be used carefully due to security and performance considerations.

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