Reflection

Analogy: concept

Reflection is like X-Ray Specs:

Normally, you can only see the outside of an object (Public methods). With Reflection, you can see the inside (Private fields), check what type it is, and even change its internal organs (Data) while it's alive!

X-Ray Specs

Inspect a "SecretBox" object to see its private fields, and then hack it!

Reflection (X-Ray Specs)

SecretBox

Private Access Only

Reflection Output

No data scanned yet.

*Reflection allows code to inspect and modify itself at runtime, even bypassing private access modifiers!

Key Concepts

Introspection: The ability of a program to examine the type or properties of an object at runtime.
Reflection: The ability to modify the structure and behavior of the program at runtime.
Use Cases:
- IDEs (Auto-completion)
- Debuggers
- Testing Frameworks (JUnit uses reflection to find @Test methods)
- Serialization Libraries (JSON parsers)

The Code

import java.lang.reflect.*;

class Secret {
    private String password = "123";
}

Secret s = new Secret();
// s.password; // Error! Private access.

// Using Reflection
Field f = s.getClass().getDeclaredField("password");
f.setAccessible(true); // Bypass security!
System.out.println(f.get(s)); // Output: "123"