Planned lessonMID-009-L03

Reflection

On This Lesson 4 topics

This lesson is planned. The outline below lists the topics it will cover. The full lesson has not been published yet.

In this lesson

inspect and invoke code at runtime.

Class<?> gives fields, methods, constructors, annotations, and modifiers.
Invoke with Method.invoke; read fields with Field.get (needs setAccessible(true) for private members, and may be blocked by modules).
Frameworks use it for dependency injection, serialization, and mapping.
Costs: slower than direct calls, bypasses compile-time checks, and can break encapsulation.
Avoid in hot paths; cache Method objects or use MethodHandle.

Draft outline details

java

for (Method m : Product.class.getDeclaredMethods()) {
    System.out.println(m.getName() + " " + m.getReturnType());
}

Why avoid reflection in hot loops?

Show answer

Slower, and checks move from compile time to runtime.

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