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Minfo.SeLab2r1.4 - 17 Oct 2012 - 16:28 - KrikavaFiliptopic end

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Lab 2 : Reflection


In this lab we will overview some of the basic principle of reflection in Java.

Create a new project in Eclipse tp2 for today's exercises.

Exercise 1 : A class analyzer

Start by copying the following source into your new Eclipse project.

Exercise 1.1 : No generics version

Write a simple class analyzer. Such an analyzer expects a name of a class and it will print to the standard output its interface: its declaration, declared fields, constructors and methods.

Here is a sample output given java.util.ArrayList as an input:

For start do not worry about generics. There is a bonus exercise for you to do if you have enough time (meaning you have completed all the other exercises) or to do at home.

  • Do not use toString() neither toGenericString() method
  • Try to work iteratively and test as you go
  • Try to refactor as you go (hint: think about a mkString method that will combine an array to a String with a separator)
  • The interactive behavior of the program is not very handy for testing. Think how can you speed up the development cycle (code/test).

Exercise 1.2 : Non interactive version

Modify the program so it can run non interactively taking its input from command line. For example I should be able to run it like:

$ java tp2.ClassAnalyzer java.util.Data java.util.ArrayList

Extra Exercise 1.3 : Generics version

Try to include the generics type information.

Extra Exercise 1.4 : Generics version with annotations

Try to include runtime annotations.

  • Think about all the places an annotation can occur
  • Print also arguments of the annotations' parameters

Extra Exercise 1.5: Global list of imports

Use only simple class names and include a list of imports right after package declaration. Think about to handle duplicates (java.util.List, java.awt.List). When you look at how Eclipse organizes the imports, it groups together same package imports, you could try to do the same.

Exercise 2 : A generic toString() method

In the creature simulator's AbstractCreature class from the previous lab write a generic toString() method:

public String toString() {...}

which will output all of the creature's attributes (fields). It has to be generic method since subclasses of the AbstractCreature can define their own attributes this class is not aware of.

  • Think what is the difference between getDeclaredFields() and getFields()
  • To test it, you can add some more attributes to the SmartCreature

Exercise 3 : Array Grow

Once you complete the method and run, you should see following output:

[1, 2, 3, 0, 0, 0]
[Maurice Chombier, Francois Pignon, null, null]
The following call will generate an exception.
Exception in thread "main" java.lang.ClassCastException: [Ljava.lang.Object; cannot be cast to [Ltp2.ArrayGrowTest2$Personne;

The nulls on the first line are fine - proving the the array has grown

  • Look at the methods from the java.util.Arrays class.

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