Type safety: Unchecked cast from Object

java casting type-safety unchecked
Matthew picture Matthew · Apr 7, 2010 · Viewed 67.7k times · Source

I try to cast an object to my Action class, but it results in a warning:

Type safety: Unchecked cast from Object to Action<ClientInterface>

Action<ClientInterface> action = null;
try {
 Object o = c.newInstance();
 if (o instanceof Action<?>) {
  action = (Action<ClientInterface>) o;
 } else {
  // TODO 2 Auto-generated catch block
  throw new InstantiationException();
 }
 [...]

Thank you for any help

Answer

Jon Skeet picture Jon Skeet · Apr 7, 2010

Yes - this is a natural consequence of type erasure. If o is actually an instance of Action<String> that won't be caught by the cast - you'll only see the problem when you try to use it, passing in a ClientInterface instead of a string.

You can get rid of the warning using:

@SuppressWarnings("unchecked")

as a function annotation, but you can't easily sort out the underlying problem :(

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