Effective Java

// List-based Chooser - typesafe
public class Chooser {
private final 
List
choiceList;
public Chooser(Collection choices) {
choiceList = 
new ArrayList<>(choices)
;
}
public T choose() {
Random rnd = ThreadLocalRandom.current();
return 
choiceList.get(rnd.nextInt(choiceList.size()))
;
}
}
This version is a tad more verbose, and perhaps a tad slower, but it’s worth it for
the peace of mind that you won’t get a 
ClassCastException
at runtime. 
In summary, arrays and generics have very different type rules. Arrays are
covariant and reified; generics are invariant and erased. As a consequence, arrays
provide runtime type safety but not compile-time type safety, and vice versa for
generics. As a rule, arrays and generics don’t mix well. If you find yourself
mixing them and getting compile-time errors or warnings, your first impulse
should be to replace the arrays with lists.

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CHAPTER 5
GENERICS
130
Item 29: Favor generic types
It is generally not too difficult to parameterize your declarations and make use of
the generic types and methods provided by the JDK. Writing your own generic
types is a bit more difficult, but it’s worth the effort to learn how.
Consider the simple (toy) stack implementation from Item 7:
Object-based_collection_-_a_prime_candidate_for_generics_public_class_Stack_{_private_Object'>// Object-based collection - a prime candidate for generics
public class Stack {
private 
Object
[] elements;
private int size = 0;
private static final int DEFAULT_INITIAL_CAPACITY = 16;
public Stack() {
elements = new 
Object
[DEFAULT_INITIAL_CAPACITY];
}
public void push(
Object
e) {
ensureCapacity();
elements[size++] = e;
}
public