// Chooser - a class badly in need of generics!
// Bloch 3rd edition, Chapter 5, Item 28: Prefer lists to arrays
public class Chooser {
private final Object[] choiceArray;
public Chooser (Collection choices) {
choiceArray = choices.toArray();
}
public Object choose() {
Random rnd = ThreadLocalRandom.current();
return choiceArray [rnd.nextInt(choiceArray.length)];
}
}
Generify by adding a type to the Chooser class
and adopting Bloch's advice about arrays and lists.
Make whatever corresponding changes are necessary.
Write a (partial) contract for the choose() method.
What's ugly about this?
Can you come up with a client-visible invariant that allows you to get rid of the precondition?
How should you capture that client-invariant with the rep-invariant?
Rewrite the contract for choose() and
supply a contract for the constructor.