This document discusses Java annotations and provides examples of their use. It explains that annotations can be used on classes, fields, methods, packages, variables, and types to provide information to compilers, for documentation purposes, code generation, and runtime processing. It also describes the @Target and @Retention meta-annotations that specify where annotations can be applied and whether they are available at compile time, class time, or runtime. The document gives examples of built-in annotations like @Deprecated and @Override as well as custom annotations.

1. @Annotations

2. Before Java 5
• transient
• comments & java doc (@deprecated)
• interfaces

3. Where to use?
• classes
• fields
• methods
• packages
• variables
• types ( from Java 8)

4. @NotNull String array1 [][];
String array2 @NotNull [][];
String array3 [] @NotNull[];
String @NotNull[][] array4;
String @NotNull [] @NotNull[] array5;
@NotNull String @NotNull[] @NotNull[] array6;

5. @NonNull String name;
List<@NonNull String> names;
class UnmodifiableList<T> implements @Readonly List<@Readonly T> {...}
email = (@Email String) input; new @Information MyObject();
void doSomething() throws @ImportantForMe MyException { ... }

6. Use cases
• Information for the compiler
• Documentation
• Code generation
• Runtime processing

7. @Retention
• SOURCE
• CLASS
• RUNTIME

8. @Target
• ANNOTATION_TYPE
• CONSTRUCTOR
• FIELD
• LOCAL_VARIABLE
• METHOD
• PACKAGE
• TYPE_USE (TYPE_PARAMETER & TYPE)

9. • @Deprecated
• @Inherited
• @Deprecated
• @SuppressWarnings
• @Override
• @SafeVarargs

10. Java 8
• @Repeatable
• @FunctionalInterface

11. Example
@Retention(RetentionPolicy.RUNTIME)
@Target({ElementType.TYPE, ElementType.PARAMETER})
public @interface Option {
String value();
Class type() default String.class;
boolean hasArg() default true;
boolean isRequired() default false;
}

12. @Demo

13. @Metaphor
public interface Life extends Box<Chocolate> {
}

14. @Oxymoron
public interface DisassemblerFactory {
Disassembler createDisassembler();
}

15. @LOL @Facepalm
@WTF("just use Collections.reverse()")
@Booyah
private static <T> void invertOrdering(List<T> list) {
for (int i = 0; i < list.size() / 2; i++) {
int j = list.size() - 1 - i;
T item1 = list.get(i);
T item2 = list.get(j);
list.set(i, item2);
list.set(j, item1);
}
}

16. @Magic
public static int negate(int n) {
return new Byte((byte) 0xFF).hashCode()
/ (int) (short) 'uFFFF' * ~0
* Character.digit ('0', 0) * n
* (Integer.MAX_VALUE * 2 + 1)
/ (Byte.MIN_VALUE >> 7) * (~1 | 1);
}

17. public void
setBonusMultiplier(@ThisHadBetterNotBe(NEGATIVE)
double multiplier) {
this.multiplier = multiplier;
}

18. @ThisWouldBeOneLineIn(
language = "haskell"
toWit = "product [1..n]")
public int factorial(int n) {
int fac = 1;
for (int i = 1; i <= n; i++) {
fac *= i;
}
return fac;
}

19. @Thanks