Tuesday, May 11, 2010

Pitfalls of Reflection

In this post I will discuss a pitfall of the use of reflection in Java. Specifically how reflection can obscure and even change the semantics of a piece of code.

What is wrong with the following example of JavaBean naming convention?

public Boolean isCorrect() {
    /* implementation not shown. */

Did you spot the capital B on the Boolean return type? According to the JavaBean naming convention the property does not fall under the special rules for booleans and should be named accordingly.

public Boolean getCorrect() {
    /* implementation not shown. */

Although there is a sleight syntactic difference, the apparent semantic difference is non-existent. According to William Shakespeare:

A rose by any other name would smell as sweet

Enter reflection. By using reflection it is possible to perform hugely different behaviour depending on the name of a method. The following whimsical example is a clear demonstration of this fact.

Class aClass = ReflectedClass.class;
Method method;
    method = aClass.getDeclaredMethod("isCorrect");
catch (NoSuchMethodException e)

So one of the pitfalls of reflection is the hidden semantics associated with code. Stated in other words: the influence of code can not be inferred by the syntactic definition of that code.

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