Java syntax
part 40/46 · 86.7 KB total
──────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────
Usage of annotations
Annotations may be used in any kind of declaration, whether it is package, class (including enums), interface (including annotations), field, method, parameter, constructor, or local variable. Also they can be used with enum constants. Annotations are declared using the @ sign preceding annotation type name, after which element-value pairs are written inside brackets. All elements with no default value must be assigned a value.
@BlockingOperations(/*mandatory*/ fileSystemOperations,
/*optional*/ networkOperations = true)
void openOutputStream() { //Annotated method
}
Besides the generic form, there are two other forms to declare an annotation, which are shorthands. Marker annotation is a short form, it is used when no values are assigned to elements:
@Unused // Shorthand for @Unused()
void travelToJupiter() {
}
The other short form is called single element annotation. It is used with annotations types containing only one element or in the case when multiple elements are present, but only one elements lacks a default value. In single element annotation form the element name is omitted and only value is written instead:
/* Equivalent for @BlockingOperations(fileSystemOperations = true).
networkOperations has a default value and
does not have to be assigned a value */
@BlockingOperations(true)
void openOutputStream() {
}
──────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────