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Reflection ( Reflexion in British English )

Reflection ( Reflexion in British English ). Mo Alkhafaji.

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Reflection ( Reflexion in British English )

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  1. Reflection(Reflexion in British English ) Mo Alkhafaji

  2. ReflectionA 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.

  3. 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.

  4. 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.

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

  6. 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.

  7. 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.

  8. Javassist • Unlike Reflection, Javassist API lets you manipulate and change byte code generated by Java compilers. • CtClass, CtMethod, and CtField. • Classes do not have to be loaded into JVM! • You can load using toClass() method in CtClass to load into JVM. • You can generate new classes and methods during runtime.

  9. Javassist – Cont. 1. ClassPool pool = ClassPool.getDefault(); 2. CtClass pt = pool.get(“mypackage.PNLParser"); 3. pt.setSuperclass(pool.get(“ReportParser")); 4. CtMethod m = CtNewMethod.make("public void printType() { System.out.println(“PNL”); }", pt); 5. pt.addMethod(m); 6. pt.writeFile();

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