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ESAMPLE @NETBEANS @LURCHI @ASL @LXI @PPM @NONNULL @NOSKILL @RASPBERRY @ARDUINO @INTERFACE @JAVA @RULEZ @NOT @CLASS @

@JAVA @ANNOTATIONS @EVERYWHERE @JAVA @FAIR @GSI @UNILAC @SIS @ESR @FLAIR @LSA10 @PYTHON @IOT @JSON @TOI @BU @BUZZWORDS @HASHTAG @WIFI @RJ45 @IMPORT @GLADOS @INCLUDE @USING @NOT42 @SUPERUSER @NOPWD @SYSDEV @JAVANOOB @NOIDEA @CONFUSION @NE

@LOBI @PRESENTER @RAINER @HASEITL @

Java Workshop 2015 - Annotations Everywhere - Rainer Haseitl

ANNOTATIONS?

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since JDK 5.0: annotations for definitions @Deprecated, @Override, @SuppressWarnings, … !Spring Framework: @Transactional @Cacheable("clientCache") !JDK 8: annotations wherever a type is used („Type Annotations“) @NonNull @Readonly @YourOwnAnnotation


EXAMPLE

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import org.checkerframework.checker.nullness.qual.*;!public class GetStarted { public static void main(String[] args) { @NonNull Object ref = new Object(); }}

using Checker Framework by University of Washington

Annotation can be written for Java < 1.8 as /*@NonNull*/ Object ref = new Object();


EXAMPLE

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import org.checkerframework.checker.nullness.qual.*;!public class GetStarted { public static void main(String[] args) { @NonNull Object ref = new Object(); // ... some code ... ref = null; }}


Checker reports: (…) incompatible types in assignment (…)


EXAMPLE

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public class GetStarted { public static void main(String[] args) { @NonNull Object ref = new Object(); Map<String, Object> myMap = new HashMap<>(); ref = myMap.get(„key"); // returns null if „key“ not found }}



EXAMPLE

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public class GetStarted { public static void main(String[] args) { @NonNull Object ref = new Object(); Map<String, Object> myMap = new HashMap<>(); ref = myMap.get(„key"); // returns null if „key“ not found }}


Checker reports: incompatible types in assignment. ref = myMap.get("key"); found : @Initialized @Nullable Object required: @UnknownInitialization @NonNull Object


ANNOTATION PLACING

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Return value: ! @Interned String intern() { ... } !!Parameter: ! int compareTo(@NonNull String other) { ... }!!receiver ("this" parameter) ! String toString(@ReadOnly MyClass this) { ... }!!generics: non-null list of interned Strings ! @NonNull List<@Interned String> messages;!!arrays: non-null array of interned Strings ! @Interned String @NonNull [] messages;!!cast ! myDate = (@ReadOnly Date) readonlyObject;


CHECKER FRAMEWORK

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Annotations in the checker framework @NonNull (never null) @Nullable (can be null) @Regex @Interned @GuardedBy (Concurrency stuff) @Tainted (indicate possibly malicious user input) Units - @s, @m, @g, @A, @K, @mol, @cd !and other fancy checkers: http://types.cs.washington.edu/checker-framework/current/checker-framework-manual.html !!available as Command Line / Eclipse Plugin / NetBeans

Integer x = new Integer(22); Integer y = new Integer(22); System.out.println(x == y); // prints false!

http://types.cs.washington.edu/checker-framework/current/checker-framework-manual.html


OWN ANNOTATIONS

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Example: @Localizable

public @interface Localizable{}

Localizable.java

@Localizablepublic class JavaAnnotations{ public static void main(String[] args) { }}

JavaAnnotations.java


OWN ANNOTATIONS

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@Localizablepublic class JavaAnnotations{ public static void main(String[] args) { System.out.println("Localizable: " + JavaAnnotations.class.isAnnotationPresent(Localizable.class)); }}



OWN ANNOTATIONS

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@Localizablepublic class JavaAnnotations{ public static void main(String[] args) { System.out.println("Localizable: " + JavaAnnotations.class.isAnnotationPresent(Localizable.class)); }}


>>> Localizable: false


OWN ANNOTATIONS

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import java.lang.annotation.Retention;import java.lang.annotation.RetentionPolicy;!@Retention(RetentionPolicy.RUNTIME)public @interface Localizable{}

Localizable.java

Source: Annotations are discarded by the compiler Class: Annotations are in class file but not kept for VM (default) Runtime: VM can read the annotations


OWN ANNOTATIONS

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Encryption example (by checker framework)public void sendPassword() { String password = getUserPassword(); sendOverInternet(password);}!// Only send encrypted data!public void sendOverInternet(@Encrypted String msg) { // ...}!private String getUserPassword() { return "!@#$Really Good Password**";}


OWN ANNOTATIONS

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Encryption example (by checker framework)public void sendPassword() { String password = getUserPassword(); sendOverInternet(password);}!// Only send encrypted data!public void sendOverInternet(@Encrypted String msg) { // ...}!private String getUserPassword() { return "!@#$Really Good Password**";}

!incompatible types in argument. sendOverInternet(password); found : @PossibleUnencrypted String required: @Encrypted String EncryptionDemo.java /encryption-checker/src/encrypted line 34 Checker Framework Problem


OWN ANNOTATIONS

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Encryption example (by checker framework)public void sendPassword() { String password = getUserPassword(); // sendOverInternet(password); sendOverInternet(encrypt(password));}!// Only send encrypted data!public void sendOverInternet(@Encrypted String msg) { // ...}!public @Encrypted String encrypt(String text) { @Encrypted String encryptedText = new @Encrypted String(); // ... encryption magic return encryptedText;}


ATTRIBUTES

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OpenBook annotation example with attributes

public @interface ListOfFilesResource{ String value();}

ListOfFileResources.java

@ListOfFilesResource( value = "/home/" ) public String[] files;

Usage:

(…)if ( field.isAnnotationPresent( ListOfFilesResource.class ) ) field.set( newInstance, new File(field.getAnnotation(ListOfFilesResource.class ).value().toString()).list() );)(…)

ResourceReader.java (custom class to fill the attributes):

not a return value but type of the attribute

/home/


ADVANCED USAGE

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@Documented@Target( ElementType.FIELD )@Retention( RetentionPolicy.RUNTIME )!public @interface UrlResource{ enum UpperLowerCase { UNCHANGED, LOWERCASE, UPPERCASE }! String value();! boolean trim() default false;! UpperLowerCase upperLowerCase() default UpperLowerCase.UNCHANGED;! Class<? extends ResourceConverter>[] converter() default { };}

UrlResource.java


ADVANCED USAGE

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@Documented@Target( ElementType.FIELD )@Retention( RetentionPolicy.RUNTIME )!public @interface UrlResource{ enum UpperLowerCase { UNCHANGED, LOWERCASE, UPPERCASE }! String value();! boolean trim() default false;! UpperLowerCase upperLowerCase() default UpperLowerCase.UNCHANGED;! Class<? extends ResourceConverter>[] converter() default { };}

UrlResource.java

annotation will show up in the documentation annotation usage is allowed for

static and object variables („FIELD“)

enum definitions are allowed

optional default values

array of subclasses of „ResourceConverter“


ADVANCED USAGE

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public @interface UrlResource{ enum UpperLowerCase { UNCHANGED, LOWERCASE, UPPERCASE } String value(); boolean trim() default false; UpperLowerCase upperLowerCase() default UpperLowerCase.UNCHANGED; Class<? extends ResourceConverter>[] converter() default { };}

UrlResource.java

@UrlResource( value = "http://url.tld/someTextFile.txt", converter = { RemoveNoWordCharactersConverter.class, SortConverter.class } ) public String testFile;

Usage:


FURTHER READING

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Project Lombok - http://projectlombok.org/ Automatic generation of Getters/Setters/Copy constructor/…

http://projectlombok.org/


REFERENCES

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Quick overview what’s new with annotations https://blogs.oracle.com/java-platform-group/entry/java_8_s_new_type !Checker Framework & Examples http://types.cs.washington.edu/checker-framework/ !Retention http://docs.oracle.com/javase/7/docs/api/java/lang/annotation/RetentionPolicy.html !Annotation Examples http://openbook.rheinwerk-verlag.de/javainsel9/javainsel_25_006.htm

@NoQuestions?!@kthxbye

https://blogs.oracle.com/java-platform-group/entry/java_8_s_new_type

http://types.cs.washington.edu/checker-framework/

http://docs.oracle.com/javase/7/docs/api/java/lang/annotation/RetentionPolicy.html

http://openbook.rheinwerk-verlag.de/javainsel9/javainsel_25_006.htm

annotations @everywhere @java @fair @gsi ... - … filejava workshop 2015 - annotations everywhere -...

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