Reflection Reflexion in British English Mo Alkhafaji Reflection

Reflection (Reflexion in British English ) Mo Alkhafaji

Reflection A powerful Java API that allows for dynamic introspection of classes, interfaces, methods, and fields. No similar built-in mechanism in Pascal, C, or C++. What can you do with Reflection? It gives you the ability to: * Discover interfaces, classes, methods and fields. * Examine and call classes, methods and constructors. * Discover types of objects. * Write very generic code.

The API * java. lang. Class — This class is used to represent classes. * java. lang. reflect. Constructor — A special class for inspecting any of a class's constructor methods. * java. lang. reflect. Method — This class provides an abstract means of invoking a Java method from a given class or object.

The API – Cont. * java. lang. reflect. Modifier — The Modifier class is used to determine whether special access modifiers (such as private, public, or protected) have been applied to a method or attribute. * java. lang. reflect. Array — This class is used as an abstract representation of array objects. * java. lang. reflect. Field — This class is used to represent an attribute field.

Practical Examples * Java. Beans. * Debuggers. * Class browsers. * Introspection. * Too generic tasks that cannot be grouped into interfaces or abstract classes.

Practical Examples - Cont. * A proxy to remote API that can change. * Changing code without recompiling it! * Specific requirements. * Artificial Intelligence (AI) in learning and dynamic generation of logic.

Disadvantages * * * Complex. You cannot use by only looking at the API. Error prone. Slow because classes, methods, and fields need to be loaded at runtime for introspection. Security. It does not update byte code.

Javassist 1. Unlike Reflection, Javassist API lets you manipulate and change byte code generated by Java compilers. 2. Ct. Class, Ct. Method, and Ct. Field. 3. Classes do not have to be loaded into JVM! 4. You can load using to. Class() method in Ct. Class to load into JVM. 5. You can generate new classes and methods during runtime.

Javassist – Cont. 1. Class. Pool pool = Class. Pool. get. Default(); 2. Ct. Class pt = pool. get(“mypackage. PNLParser"); 3. pt. set. Superclass(pool. get(“Report. Parser")); 4. Ct. Method m = Ct. New. Method. make("public void print. Type() { System. out. println(“PNL”); }", pt); 5. pt. add. Method(m); 6. pt. write. File();