Which three annotation uses are valid? (Choose three.)

Question

Options

• AFunction<String, String> func = (@NonNull x) -> x.toUpperCase();
• Bvar v = "Hello" + (@Interned) "World";
• Cvar integers = new List<(@NonNull Integer) x>();
• DFunction<String, String> func = (@NonNull Function<String, String> x) -> x.toUpperCase();
• Evar str = (@NonNull String) str;
• Fvar myObj = (@NonNull MyObject) myObj;

• A
  3% (1)
• B
  3% (1)
• C
  14% (4)
• D
  79% (23)

Explanation

Options D, E, and F are valid because Java type annotations (JSR 308) are permitted in two specific locations demonstrated here: explicitly-typed lambda parameters (D) and cast expressions (E, F). In D, @NonNull annotates the lambda parameter because the full type Function<String, String> is explicitly declared - this is required for a parameter-level annotation in a lambda. In E and F, @NonNull annotates the cast type directly, which is a well-defined annotation target per the Java specification.

The distractors fail for distinct reasons: A is invalid because you cannot annotate an inferred lambda parameter - omitting the type (just x) means there is no type element to annotate, so the type must be written out explicitly as in D. B is syntactically malformed - (@Interned) has no type inside the parentheses, so it is not a valid cast expression (it would need to be (@Interned String) "World"). C is invalid because (@NonNull Integer) x is a cast expression placed inside a generic type argument position, which is not legal syntax - the correct form would be new ArrayList<@NonNull Integer>().

Memory tip: Type annotations need a type to attach to. Remember "No type, no annotation" - if the type is absent or the syntax puts the annotation where no type element exists (empty parens, inside <...> as a cast), the annotation is invalid.

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