Effective Java 24 Eliminate unchecked warnings

Note

1. Eliminate every unchecked warning that you can.

   Set<Lark> exaltation = new HashSet();

   The compiler will gently remind you what you did wrong:

   Venery.java:4: warning: [unchecked] unchecked conversion

   found : HashSet, required: Set<Lark>

   Set<Lark> exaltation = new HashSet();

   ^

   You can then make the indicated correction, causing the warning to disappear:

   Set<Lark> exaltation = new HashSet<Lark>();

2. If you can't eliminate a warning, and you can prove that the code that provoked the warning is type safe, then (and only then) suppress the warning with an @SuppressWarnings("unchecked") annotation.
3. Always use the Suppress Warnings annotation on the smallest scope possible.

   // Adding local variable to reduce scope of @SuppressWarnings

   public <T> T[] toArray(T[] a) {

   if (a.length < size) {

   // This cast is correct because the array we're creating

   // is of the same type as the one passed in, which is T[].

   @SuppressWarnings("unchecked") T[] result =

   (T[]) Arrays.copyOf(elements, size, a.getClass());

   return result;

   }

   System.arraycopy(elements, 0, a, 0, size);

   if (a.length > size)

   a[size] = null;

   return a;

   }

4. Every time you use an @SuppressWarnings("unchecked") annotation, add a comment saying why it's safe to do so.

Summary

Unchecked warnings are important. Don't ignore them. Every unchecked warning represents the potential for a ClassCastException at run-time. Do your best to eliminate these warnings. If you can't eliminate an unchecked warning and you can prove that the code that provoked it is typesafe, suppress the warning with an @SuppressWarnings("unchecked") annotation in the narrowest possible scope. Record the rationale for your decision to suppress the warning in a comment.