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+---
+title: Annotations
+layout: default
+chapter: 11
+---
+
+# Annotations
+
+```ebnf
+  Annotation       ::=  ‘@’ SimpleType {ArgumentExprs}
+  ConstrAnnotation ::=  ‘@’ SimpleType ArgumentExprs
+```
+
+## Definition
+
+Annotations associate meta-information with definitions.
+A simple annotation has the form `@$c$` or `@$c(a_1 , \ldots , a_n)$`.
+Here, $c$ is a constructor of a class $C$, which must conform
+to the class `scala.Annotation`.
+
+Annotations may apply to definitions or declarations, types, or
+expressions.  An annotation of a definition or declaration appears in
+front of that definition.  An annotation of a type appears after
+that type. An annotation of an expression $e$ appears after the
+expression $e$, separated by a colon. More than one annotation clause
+may apply to an entity. The order in which these annotations are given
+does not matter.
+
+Examples:
+
+```scala
+@deprecated("Use D", "1.0") class C { ... } // Class annotation
+@transient @volatile var m: Int             // Variable annotation
+String @local                               // Type annotation
+(e: @unchecked) match { ... }               // Expression annotation
+```
+
+## Predefined Annotations
+
+### Java Platform Annotations
+
+The meaning of annotation clauses is implementation-dependent. On the
+Java platform, the following annotations have a standard meaning.
+
+  * `@transient` Marks a field to be non-persistent; this is
+    equivalent to the `transient`
+    modifier in Java.
+
+  * `@volatile` Marks a field which can change its value
+    outside the control of the program; this
+    is equivalent to the `volatile`
+    modifier in Java.
+
+  * `@SerialVersionUID(<longlit>)` Attaches a serial version identifier (a
+    `long` constant) to a class.
+    This is equivalent to a the following field
+    definition in Java:
+
+    ```
+    private final static SerialVersionUID = <longlit>
+    ```
+
+  * `@throws(<classlit>)` A Java compiler checks that a program contains handlers for checked exceptions
+    by analyzing which checked exceptions can result from execution of a method or
+    constructor. For each checked exception which is a possible result, the
+    `throws`
+    clause for the method or constructor must mention the class of that exception
+    or one of the superclasses of the class of that exception.
+
+### Java Beans Annotations
+
+  * `@scala.beans.BeanProperty` When prefixed to a definition of some variable `X`, this
+    annotation causes getter and setter methods `getX`, `setX`
+    in the Java bean style to be added in the class containing the
+    variable. The first letter of the variable appears capitalized after
+    the `get` or `set`. When the annotation is added to the
+    definition of an immutable value definition `X`, only a getter is
+    generated. The construction of these methods is part of
+    code-generation; therefore, these methods become visible only once a
+    classfile for the containing class is generated.
+
+  * `@scala.beans.BooleanBeanProperty` This annotation is equivalent to `scala.reflect.BeanProperty`, but
+    the generated getter method is named `isX` instead of `getX`.
+
+### Deprecation Annotations
+
+  * `@deprecated(message: <stringlit>, since: <stringlit>)`<br/>
+    Marks a definition as deprecated. Accesses to the
+    defined entity will then cause a deprecated warning mentioning the
+    _message_ `<stringlit>` to be issued from the compiler.
+    The argument _since_ documents since when the definition should be considered deprecated.<br/>
+    Deprecated warnings are suppressed in code that belongs itself to a definition
+    that is labeled deprecated.
+
+  * `@deprecatedName(name: <symbollit>)`<br/>
+    Marks a formal parameter name as deprecated. Invocations of this entity
+    using named parameter syntax refering to the deprecated parameter name cause a deprecation warning.
+
+### Scala Compiler Annotations
+
+  * `@unchecked` When applied to the selector of a `match` expression,
+    this attribute suppresses any warnings about non-exhaustive pattern
+    matches which would otherwise be emitted. For instance, no warnings
+    would be produced for the method definition below.
+
+    ```
+    def f(x: Option[Int]) = (x: @unchecked) match {
+    case Some(y) => y
+    }
+    ```
+
+    Without the `@unchecked` annotation, a Scala compiler could
+    infer that the pattern match is non-exhaustive, and could produce a
+    warning because `Option` is a `sealed` class.
+
+  * `@uncheckedStable` When applied a value declaration or definition, it allows the defined
+    value to appear in a path, even if its type is [volatile](03-types.html#volatile-types).
+    For instance, the following member definitions are legal:
+
+    ```
+    type A { type T }
+    type B
+    @uncheckedStable val x: A with B // volatile type
+    val y: x.T                       // OK since `x' is still a path
+    ```
+
+    Without the `@uncheckedStable` annotation, the designator `x`
+    would not be a path since its type `A with B` is volatile. Hence,
+    the reference `x.T` would be malformed.
+
+    When applied to value declarations or definitions that have non-volatile
+    types, the annotation has no effect.
+
+  * `@specialized` When applied to the definition of a type parameter, this annotation causes
+    the compiler
+    to generate specialized definitions for primitive types. An optional list of
+    primitive
+    types may be given, in which case specialization takes into account only
+    those types.
+    For instance, the following code would generate specialized traits for
+    `Unit`, `Int` and `Double`
+
+    ```
+    trait Function0[@specialized(Unit, Int, Double) T] {
+      def apply: T
+    }
+    ```
+
+    Whenever the static type of an expression matches a specialized variant of
+    a definition, the compiler will instead use the specialized version.
+    See the [specialization sid](http://docs.scala-lang.org/sips/completed/scala-specialization.html) for more details of the implementation.
+
+## User-defined Annotations
+
+Other annotations may be interpreted by platform- or
+application-dependent tools. Class `scala.Annotation` has two
+sub-traits which are used to indicate how these annotations are
+retained. Instances of an annotation class inheriting from trait
+`scala.ClassfileAnnotation` will be stored in the generated class
+files. Instances of an annotation class inheriting from trait
+`scala.StaticAnnotation` will be visible to the Scala type-checker
+in every compilation unit where the annotated symbol is accessed. An
+annotation class can inherit from both `scala.ClassfileAnnotation`
+and `scala.StaticAnnotation`. If an annotation class inherits from
+neither `scala.ClassfileAnnotation` nor
+`scala.StaticAnnotation`, its instances are visible only locally
+during the compilation run that analyzes them.
+
+Classes inheriting from `scala.ClassfileAnnotation` may be
+subject to further restrictions in order to assure that they can be
+mapped to the host environment. In particular, on both the Java and
+the .NET platforms, such classes must be toplevel; i.e. they may not
+be contained in another class or object.  Additionally, on both
+Java and .NET, all constructor arguments must be constant expressions.