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IDEs may also highlight this method somehow as deprecated")]),t._v(" "),s("div",{staticClass:"language-java extra-class"},[s("pre",{pre:!0,attrs:{class:"language-java"}},[s("code",[s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("class")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("ComplexAlgorithm")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n    "),s("span",{pre:!0,attrs:{class:"token annotation punctuation"}},[t._v("@Deprecated")]),t._v("\n    "),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("public")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("void")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("oldSlowUnthreadSafeMethod")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n        "),s("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// stuff here")]),t._v("\n    "),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("\n    \n    "),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("public")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("void")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("quickThreadSafeMethod")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n        "),s("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// client code should use this instead")]),t._v("\n    "),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("\n"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("\n\n")])])]),s("p",[s("strong",[t._v("@SuppressWarnings")])]),t._v(" "),s("p",[t._v("In almost all cases, when the compiler emits a warning, the most appropriate action is to fix the cause. In some instances (Generics code using untype-safe pre-generics code, for example) this may not\nbe possible and it's better to suppress those warnings that you expect and cannot fix, so you can more clearly see unexpected warnings.")]),t._v(" "),s("p",[t._v("This annotation can be applied to a whole class, method or line. It takes the category of warning as a parameter.")]),t._v(" "),s("div",{staticClass:"language-java extra-class"},[s("pre",{pre:!0,attrs:{class:"language-java"}},[s("code",[s("span",{pre:!0,attrs:{class:"token annotation punctuation"}},[t._v("@SuppressWarnings")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token string"}},[t._v('"deprecation"')]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v("\n"),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("public")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("class")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("RiddledWithWarnings")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n    "),s("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// several methods calling deprecated code here")]),t._v("\n"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("\n\n"),s("span",{pre:!0,attrs:{class:"token annotation punctuation"}},[t._v("@SuppressWarning")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token string"}},[t._v('"finally"')]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v("\n"),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("public")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("boolean")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("checkData")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n    "),s("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// method calling return from within finally block")]),t._v("\n"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("\n\n")])])]),s("p",[t._v("It is better to limit the scope of the annotation as much as possible, to prevent unexpected warnings also being suppressed. 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Only the "),s("code",[t._v("unchecked")]),t._v(" and "),s("code",[t._v("deprecation")]),t._v(" warnings are specifically mentioned in the JLS. Unrecognized warning types will be ignored.")]),t._v(" "),s("p",[s("strong",[t._v("@SafeVarargs")])]),t._v(" "),s("p",[t._v("Because of type erasure, "),s("code",[t._v("void method(T... t)")]),t._v(" will be converted to "),s("code",[t._v("void method(Object[] t)")]),t._v(" meaning that the compiler is not always able to verify that the use of varargs is type-safe. 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This obviously hides the warning if your use is unsafe too.")]),t._v(" "),s("p",[s("strong",[t._v("@FunctionalInterface")])]),t._v(" "),s("p",[t._v("This is an optional annotation used to mark a FunctionalInterface. It will cause the compiler to complain if it does not conform to the FunctionalInterface spec (has a single     abstract method)")]),t._v(" "),s("div",{staticClass:"language-java extra-class"},[s("pre",{pre:!0,attrs:{class:"language-java"}},[s("code",[s("span",{pre:!0,attrs:{class:"token annotation punctuation"}},[t._v("@FunctionalInterface")]),t._v("\n"),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("public")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("interface")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("ITrade")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n  "),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("public")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("boolean")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("check")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("Trade")]),t._v(" t"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("\n\n"),s("span",{pre:!0,attrs:{class:"token annotation punctuation"}},[t._v("@FunctionalInterface")]),t._v("\n"),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("public")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("interface")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("Predicate")]),s("span",{pre:!0,attrs:{class:"token generics"}},[s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("<")]),s("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("T")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(">")])]),t._v(" "),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n  "),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("boolean")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("test")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("T")]),t._v(" t"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("\n\n")])])]),s("h2",{attrs:{id:"the-idea-behind-annotations"}},[s("a",{staticClass:"header-anchor",attrs:{href:"#the-idea-behind-annotations"}},[t._v("#")]),t._v(" The idea behind Annotations")]),t._v(" "),s("p",[t._v("The "),s("a",{attrs:{href:"https://docs.oracle.com/javase/specs/jls/se8/html/jls-9.html#jls-9.7",target:"_blank",rel:"noopener noreferrer"}},[t._v("Java Language Specification"),s("OutboundLink")],1),t._v(" describes Annotations as follows:")]),t._v(" "),s("blockquote"),t._v(" "),s("p",[t._v("An annotation is a marker which associates information with a program construct, but has no effect at run time.")]),t._v(" "),s("p",[t._v("Annotations may appear before types or declarations. It is possible for them to appear in a place where they could apply to both a type or a declaration."),s("br"),t._v('\nWhat exactly an annotation applies to is governed by the "meta-annotation" '),s("code",[t._v("@Target")]),t._v(". See "),s("a",{attrs:{href:"https://stackoverflow.com/documentation/java/157/annotations/2060/defining-annotation-types#t=201609121335564579697",target:"_blank",rel:"noopener noreferrer"}},[t._v('"Defining annotation types"'),s("OutboundLink")],1),t._v(" for more information.")]),t._v(" "),s("p",[t._v("Annotations are used for a multitude of purposes. Frameworks like Spring and Spring-MVC make use of annotations to define where Dependencies should be injected or where requests should be routed.")]),t._v(" "),s("p",[t._v("Other frameworks use annotations for code-generation. Lombok and JPA are prime examples, that use annotations to generate Java (and SQL) code.")]),t._v(" "),s("p",[t._v("This topic aims to provide a comprehensive overview of:")]),t._v(" "),s("li",[t._v("\nHow to define your own Annotations?\n")]),t._v(" "),s("li",[t._v("\nWhat Annotations does the Java Language provide?\n")]),t._v(" "),s("li",[t._v("\nHow are Annotations used in practice?\n")]),t._v(" "),s("h2",{attrs:{id:"compile-time-processing-using-annotation-processor"}},[s("a",{staticClass:"header-anchor",attrs:{href:"#compile-time-processing-using-annotation-processor"}},[t._v("#")]),t._v(" Compile time processing using annotation processor")]),t._v(" "),s("p",[t._v("This example demonstrates how to do compile time checking of an annotated element.")]),t._v(" "),s("h3",{attrs:{id:"the-annotation"}},[s("a",{staticClass:"header-anchor",attrs:{href:"#the-annotation"}},[t._v("#")]),t._v(" The annotation")]),t._v(" "),s("p",[t._v("The "),s("code",[t._v("@Setter")]),t._v(" annotation is a marker can be applied to methods. 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The file needs to include the fully qualified name of the annotation processor, i.e. it should look like this")]),t._v(" "),s("div",{staticClass:"language-java extra-class"},[s("pre",{pre:!0,attrs:{class:"language-java"}},[s("code",[s("span",{pre:!0,attrs:{class:"token class-name"}},[s("span",{pre:!0,attrs:{class:"token namespace"}},[t._v("annotation"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("processor"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")])]),t._v("SetterProcessor")]),t._v("\n\n")])])]),s("p",[s("strong",[t._v("We'll assume the jar file is called "),s("code",[t._v("AnnotationProcessor.jar")]),t._v(" below.")])]),t._v(" "),s("h3",{attrs:{id:"example-annotated-class"}},[s("a",{staticClass:"header-anchor",attrs:{href:"#example-annotated-class"}},[t._v("#")]),t._v(" Example annotated class")]),t._v(" "),s("p",[t._v("The following class is example class in the default package with the annotations being applied to the correct elements according to the retention policy. 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No "),s("code",[t._v(".class")]),t._v(" file is created.")]),t._v(" "),s("p",[t._v("This could be prevented by specifying the "),s("code",[t._v("-proc:none")]),t._v(" option for "),s("code",[t._v("javac")]),t._v(". You could also forgo the usual compilation by specifying "),s("code",[t._v("-proc:only")]),t._v(" instead.")]),t._v(" "),s("h3",{attrs:{id:"ide-integration"}},[s("a",{staticClass:"header-anchor",attrs:{href:"#ide-integration"}},[t._v("#")]),t._v(" IDE integration")]),t._v(" "),s("h3",{attrs:{id:"netbeans"}},[s("a",{staticClass:"header-anchor",attrs:{href:"#netbeans"}},[t._v("#")]),t._v(" Netbeans")]),t._v(" "),s("p",[t._v("Annotation processors can be used in the NetBeans editor. 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punctuation"}},[t._v(")")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("getClass")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("getAnnotation")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("UninheritedAnnotationType")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("class")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\n")])])]),s("p",[t._v("will print a result similar to this (depending on the packages of the annotation):")]),t._v(" "),s("div",{staticClass:"language-java extra-class"},[s("pre",{pre:!0,attrs:{class:"language-java"}},[s("code",[s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("null")]),t._v("\n"),s("span",{pre:!0,attrs:{class:"token annotation punctuation"}},[t._v("@InheritedAnnotationType")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v("\n"),s("span",{pre:!0,attrs:{class:"token annotation punctuation"}},[t._v("@InheritedAnnotationType")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v("\n_________________________________\n"),s("span",{pre:!0,attrs:{class:"token annotation punctuation"}},[t._v("@UninheritedAnnotationType")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token 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"),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("default")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token string"}},[t._v('"foo"')]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n    "),s("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("String")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("value")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("default")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token string"}},[t._v('"bar"')]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("\n\n\n"),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("class")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("AnnotationExample")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n    "),s("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// Put the Annotation on the method, but leave the defaults")]),t._v("\n    "),s("span",{pre:!0,attrs:{class:"token annotation punctuation"}},[t._v("@MyAnnotation")]),t._v("\n    "),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("public")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("void")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("testDefaults")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("throws")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("Exception")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n        "),s("span",{pre:!0,attrs:{class:"token comment"}},[t._v('// Using reflection, get the public method "testDefaults", which is this method with no args')]),t._v("\n        "),s("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("Method")]),t._v(" method "),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("AnnotationExample")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("class")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("getMethod")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token string"}},[t._v('"testDefaults"')]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("null")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),s("span",{pre:!0,attrs:{class:"token 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"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n        "),s("span",{pre:!0,attrs:{class:"token comment"}},[t._v('// Using reflection, get the public method "testValues", which is this method with no args')]),t._v("\n        "),s("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("Method")]),t._v(" method "),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("AnnotationExample")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("class")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("getMethod")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token string"}},[t._v('"testValues"')]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("null")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\n        "),s("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// Fetch the Annotation that is of type MyAnnotation from the Method")]),t._v("\n        "),s("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("MyAnnotation")]),t._v(" annotation "),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("MyAnnotation")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v("method"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("getAnnotation")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token 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"),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("print")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("MyAnnotation")]),t._v(" annotation"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n        "),s("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// Fetch the MyAnnotation 'key' & 'value' properties, and print them out ")]),t._v("\n        "),s("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("System")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("out"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("println")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),t._v("annotation"),s("span",{pre:!0,attrs:{class:"token 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"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("\n    "),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("\n"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("\n\n")])])]),s("p",[t._v("The output will be")]),t._v(" "),s("div",{staticClass:"language-java extra-class"},[s("pre",{pre:!0,attrs:{class:"language-java"}},[s("code",[t._v("foo "),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" bar\nbaz "),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" buzz\n\n")])])]),s("h2",{attrs:{id:"annotations-for-this-and-receiver-parameters"}},[s("a",{staticClass:"header-anchor",attrs:{href:"#annotations-for-this-and-receiver-parameters"}},[t._v("#")]),t._v(" Annotations for 'this' and receiver parameters")]),t._v(" "),s("p",[t._v("When Java annotations were first introduced there was no provision for annotating the target of an instance method or the hidden constructor parameter for an inner classes constructor.  This was remedied in Java 8 with addition of "),s("strong",[t._v("receiver parameter")]),t._v(" declarations; see "),s("a",{attrs:{href:"http://docs.oracle.com/javase/specs/jls/se8/html/jls-8.html#jls-8.4.1-220",target:"_blank",rel:"noopener noreferrer"}},[t._v("JLS 8.4.1"),s("OutboundLink")],1),t._v(".")]),t._v(" "),s("blockquote"),t._v(" "),s("p",[t._v("The receiver parameter is an optional syntactic device for an instance method or an inner class's constructor. For an instance method, the receiver parameter represents the object for which the method is invoked. For an inner class's constructor, the receiver parameter represents the immediately enclosing instance of the newly constructed object. Either way, the receiver parameter exists solely to allow the type of the represented object to be denoted in source code, so that the type may be annotated. The receiver parameter is not a formal parameter; more precisely, it is not a declaration of any kind of variable (§4.12.3), it is never bound to any value passed as an argument in a method invocation expression or qualified class instance creation expression, and it has no effect whatsoever at run time.")]),t._v(" "),s("p",[t._v("The following example illustrates the syntax for both kinds of receiver parameter:")]),t._v(" "),s("div",{staticClass:"language-java extra-class"},[s("pre",{pre:!0,attrs:{class:"language-java"}},[s("code",[s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("public")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("class")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("Outer")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n    "),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("public")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("class")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("Inner")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n        "),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("public")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("Inner")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("Outer")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("this")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n           "),s("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// ...")]),t._v("\n        "),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("\n        "),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("public")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("void")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("doIt")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("Inner")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("this")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n           "),s("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// ...")]),t._v("\n        "),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("\n    "),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("\n"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("\n\n")])])]),s("p",[t._v("The sole purpose of receiver parameters is to allow you to add annotations.  For example, you might have a custom annotation "),s("code",[t._v("@IsOpen")]),t._v(" whose purpose is to assert that a "),s("code",[t._v("Closeable")]),t._v(" object has not been closed when a method is called.  For example:")]),t._v(" "),s("div",{staticClass:"language-java extra-class"},[s("pre",{pre:!0,attrs:{class:"language-java"}},[s("code",[s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("public")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("class")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("MyResource")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("extends")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("Closeable")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n    "),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("public")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("void")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("update")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token annotation punctuation"}},[t._v("@IsOpen")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("MyResource")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("this")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("int")]),t._v(" value"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n        "),s("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// ...")]),t._v("\n    "),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("\n\n    "),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("public")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("void")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("close")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n        "),s("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// ...")]),t._v("\n    "),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("\n"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("\n\n")])])]),s("p",[t._v("At one level, the "),s("code",[t._v("@IsOpen")]),t._v(" annotation on "),s("code",[t._v("this")]),t._v(" could simply serve as documentation.  However, we could potentially do more.  For example:")]),t._v(" "),s("ul",[s("li",[t._v("An annotation processor could insert a runtime check that "),s("code",[t._v("this")]),t._v(" is not in closed state when "),s("code",[t._v("update")]),t._v(" is called.")]),t._v(" "),s("li",[t._v("A code checker could perform a static code analysis to find cases where "),s("code",[t._v("this")]),t._v(" "),s("strong",[t._v("could be")]),t._v(" closed when "),s("code",[t._v("update")]),t._v(" is called.")])]),t._v(" "),s("h2",{attrs:{id:"add-multiple-annotation-values"}},[s("a",{staticClass:"header-anchor",attrs:{href:"#add-multiple-annotation-values"}},[t._v("#")]),t._v(" Add multiple annotation values")]),t._v(" "),s("p",[t._v("An Annotation parameter can accept multiple values if it is defined as an array. For example the standard annotation "),s("code",[t._v("@SuppressWarnings")]),t._v(" is defined like this:")]),t._v(" "),s("div",{staticClass:"language-java extra-class"},[s("pre",{pre:!0,attrs:{class:"language-java"}},[s("code",[s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("public")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token annotation punctuation"}},[t._v("@interface")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("SuppressWarnings")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n    "),s("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("String")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("[")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("]")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("value")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("\n\n")])])]),s("p",[t._v("The "),s("code",[t._v("value")]),t._v(" parameter is an array of Strings. You can set multiple values by using a notation similar to Array initializers:")]),t._v(" "),s("div",{staticClass:"language-java extra-class"},[s("pre",{pre:!0,attrs:{class:"language-java"}},[s("code",[s("span",{pre:!0,attrs:{class:"token annotation punctuation"}},[t._v("@SuppressWarnings")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),s("span",{pre:!0,attrs:{class:"token string"}},[t._v('"unused"')]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v("\n"),s("span",{pre:!0,attrs:{class:"token annotation punctuation"}},[t._v("@SuppressWarnings")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),s("span",{pre:!0,attrs:{class:"token string"}},[t._v('"unused"')]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token string"}},[t._v('"javadoc"')]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v("\n\n")])])]),s("p",[t._v("If you only need to set a single value, the brackets can be omitted:")]),t._v(" "),s("div",{staticClass:"language-java extra-class"},[s("pre",{pre:!0,attrs:{class:"language-java"}},[s("code",[s("span",{pre:!0,attrs:{class:"token annotation punctuation"}},[t._v("@SuppressWarnings")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token string"}},[t._v('"unused"')]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" \n\n")])])]),s("h4",{attrs:{id:"syntax"}},[s("a",{staticClass:"header-anchor",attrs:{href:"#syntax"}},[t._v("#")]),t._v(" Syntax")]),t._v(" "),s("ul",[s("li",[t._v("@AnnotationName // 'Marker annotation' (no parameters)")]),t._v(" "),s("li",[t._v("@AnnotationName(someValue) // sets parameter with the name 'value'")]),t._v(" "),s("li",[t._v("@AnnotationName(param1 = value1) // named parameter")]),t._v(" "),s("li",[t._v("@AnnotationName(param1 = value1, param2 = value2) // multiple named parameters")]),t._v(" "),s("li",[t._v("@AnnotationName(param1 = {1, 2, 3}) // named array parameter")]),t._v(" "),s("li",[t._v("@AnnotationName({value1}) // array with single element as parameter with the name 'value'")])]),t._v(" "),s("h4",{attrs:{id:"remarks"}},[s("a",{staticClass:"header-anchor",attrs:{href:"#remarks"}},[t._v("#")]),t._v(" Remarks")]),t._v(" "),s("h3",{attrs:{id:"parameter-types"}},[s("a",{staticClass:"header-anchor",attrs:{href:"#parameter-types"}},[t._v("#")]),t._v(" Parameter types")]),t._v(" "),s("p",[t._v("Only constant expressions of following types are allowed for parameters, as well as arrays of these types:")]),t._v(" "),s("ul",[s("li",[s("code",[t._v("String")])]),t._v(" "),s("li",[s("code",[t._v("Class")])]),t._v(" "),s("li",[t._v("primitive types")]),t._v(" "),s("li",[t._v("Enum types")]),t._v(" "),s("li",[t._v("Annotation Types")])])])}),[],!1,null,null,null);a.default=e.exports}}]);