Chapter SIXTEEN
Annotations

Answers

1. The correct answer is D.

Explanation:

• A) @Annotation MyAnnotation { String value(); }
  • This option is incorrect. Java doesn’t use @Annotation to define custom annotations.
• B) interface MyAnnotation { String value(); }
  • This option is incorrect. It defines a regular interface, not an annotation. The @interface keyword is missing.
• C) @interface MyAnnotation { String value() default ""; }
  • This option is incorrect. This defines an annotation with an optional String element named value (due to the default value), not a required one.
• D) @interface MyAnnotation { String value(); }
  • This option is correct. This is the correct syntax for defining a custom annotation in Java with a required String element named value. It uses the @interface keyword to declare an annotation type and includes a method declaration for the required value element.
• E) class @MyAnnotation { public String value(); }
  • This option is incorrect. It attempts to define a class, not an annotation, and the @ symbol is misplaced.

2. The correct answer is B.

Explanation:

• A) @Override is required when implementing a method from an interface.
  • This option is incorrect. While @Override can be used when implementing a method from an interface, it is not required. It’s optional but recommended for clarity and compile-time checks.
• B) @Override helps catch errors at compile-time if a method doesn’t actually override a superclass method.
  • This option is correct. The primary purpose of @Override is to help catch errors at compile-time. If a method annotated with @Override doesn’t actually override or implement a method from a superclass or interface, the compiler will generate an error. This helps prevent errors due to typos in method names or incorrect method signatures.
• C) @Override can be used to override static methods in a superclass.
  • This option is incorrect. Static methods cannot be overridden in Java, they can only be hidden. Therefore, @Override cannot be used with static methods.
• D) @Override is mandatory when extending an abstract class and implementing its abstract methods.
  • This option is incorrect. While @Override can be used when implementing abstract methods from a superclass, it is not mandatory. It’s a good practice, but the code will compile without it.
• E) @Override allows a subclass to override final methods in its superclass.
  • This option is incorrect. Final methods cannot be overridden in Java. Using @Override on a method that attempts to override a final method will result in a compile-time error.

3. The correct answer is D.

Explanation:

• A) The code will not compile because @FunctionalInterface requires exactly two abstract methods.
  • This option is incorrect. @FunctionalInterface requires exactly one abstract method, not two. The interface Processor correctly has only one abstract method (process).
• B) The @FunctionalInterface annotation ensures that the interface can have multiple abstract methods.
  • This option is incorrect. The @FunctionalInterface annotation actually ensures that the interface has exactly one abstract method, not multiple. It’s used to indicate that an interface is intended to be a functional interface.
• C) The code will not compile because @FunctionalInterface cannot be used with interfaces that have default methods.
  • This option is incorrect. @FunctionalInterface can be used with interfaces that have default methods. The presence of default methods doesn’t affect the functional interface status as long as there’s only one abstract method.
• D) The code will compile and run, outputting "HELLO" to the console.
  • This option is correct. The code will compile and run successfully. The Processor interface is a valid functional interface with one abstract method process. The lambda expression s -> s.toUpperCase() implements this method. When upperCase.process("hello") is called, it will return "HELLO", which is then printed to the console.
• E) The code will compile but throw a runtime exception when trying to use a lambda expression with Processor.
  • This option is incorrect. The code compiles successfully and will not throw a runtime exception. The lambda expression is a valid implementation of the Processor functional interface.

4. The correct answer is C.

Explanation:

• A) @Deprecated causes the compiler to remove the annotated element from the compiled bytecode.
  • This option is incorrect. The @Deprecated annotation does not cause the compiler to remove the annotated element. It only marks the element as deprecated, but the element remains in the bytecode.
• B) @Deprecated can only be applied to methods and fields, not classes or interfaces.
  • This option is incorrect. The @Deprecated annotation can be applied to various program elements including classes, interfaces, methods, constructors, fields, and even packages, not just methods and fields.
• C) @Deprecated(since="11", forRemoval=true) indicates that the annotated element is deprecated and is scheduled for removal in a future version.
  • This option is correct. The @Deprecated annotation with parameters since and forRemoval was introduced in Java 9. When forRemoval is set to true, it indicates that the annotated element is not only deprecated but is also planned to be removed in a future version. The since parameter specifies the version in which the element was first deprecated.
• D) Using a deprecated element in your code will always result in a compile-time error.
  • This option is incorrect. Using a deprecated element typically results in a compiler warning, not an error. The code will still compile and run, but the IDE and compiler will issue warnings about the usage of deprecated elements.
• E) @Deprecated automatically provides a replacement for the deprecated element.
  • This option is incorrect. The @Deprecated annotation itself does not provide a replacement for the deprecated element. It’s a good practice to document the replacement in the associated javadoc comment, but this is not automatically handled by the annotation.

5. The correct answer is A.

Explanation:

• A) The @SuppressWarnings("deprecation") annotation will prevent compiler warnings about the use of the deprecated Date constructor.
  • This option is correct. The @SuppressWarnings("deprecation") annotation is used to suppress compiler warnings related to the use of deprecated APIs. In this case, it will prevent warnings about the use of the deprecated Date(int year, int month, int date) constructor.
• B) The @SuppressWarnings annotation in genericMethod() will cause a compile-time error due to incorrect syntax.
  • This option is incorrect. The syntax for @SuppressWarnings({"unchecked", "rawtypes"}) is correct. It’s valid to specify multiple warning types to suppress by using an array notation.
• C) The @SuppressWarnings("deprecation") annotation will automatically update the code to use non-deprecated methods.
  • This option is incorrect. The @SuppressWarnings annotation only suppresses warnings; it does not modify or update the code in any way.
• D) The @SuppressWarnings annotations in this code will suppress all compiler warnings for the entire class.
  • This option is incorrect. The @SuppressWarnings annotations in this code are method-level annotations, so they only affect the methods they’re attached to, not the entire class.
• E) The @SuppressWarnings({"unchecked", "rawtypes"}) annotation is unnecessary because the code in genericMethod() is type-safe.
  • This option is incorrect. The code in genericMethod() is not type-safe. It’s using raw types (List instead of List<?> or a specific type), and adding elements of different types to the list. The @SuppressWarnings({"unchecked", "rawtypes"}) annotation is appropriately used here to suppress warnings about these issues.

6. The correct answer is B.

Explanation:

• A) The @SafeVarargs annotation automatically checks for type safety violations at runtime.
  • This option is incorrect. @SafeVarargs does not perform runtime checks. It’s a compile-time annotation that suppresses warnings and doesn’t affect runtime behavior.
• B) @SafeVarargs can be applied to private instance methods, in addition to static methods, final instance methods, and constructors.
  • This option is correct. Java 9 introduced the ability to use @SafeVarargs on private instance methods. This is because private methods, like static and final methods, cannot be overridden, making them safe for this annotation.
• C) Using @SafeVarargs on a method prevents it from being overridden in subclasses.
  • This option is incorrect. @SafeVarargs does not affect method overriding. It’s used to suppress warnings about potential heap pollution, not to control inheritance behavior.
• D) @SafeVarargs is required on all methods that use generic varargs to ensure type safety.
  • This option is incorrect. While @SafeVarargs is often used with generic varargs methods, it’s not required on all such methods. It should only be used when the developer has ensured that the method is actually safe and doesn’t perform unsafe operations on the varargs parameter.