1. Customize annotation type
(1) Define annotation type
l Using @Interface declaration Annotation Type
Public @Interface inprogress {
}
l Use annotation type
Public class testannotation {
@Inprocess
Public void test () {
}
}
l If the annotation type and the class using it are not in the same package, you can use the IMPORT Annotation type to use @Inprogress directly.
(2) Add member
l Annotation Types can have a member variable to provide useful information
l Defining data members do not need to define getter and setter methods, just define a method named by a member name and specify the type of data required to return.
l Simple example:
Public @Interface Todo {
String value ();
}
l Use the Annotation type with a member:
Public class testannotation {
@Inprocess
@Todo ("Need to Finish this Method Later")
Public void test () {
}
}
(3) Set the default value
l Set the default value for members of the Annotation type, you need to use the default key when declared members:
Public @Interface grouptodo {
Public enum severity {
Critical, Important, Trivial, Documentation
}
Severity severity () Default severity.important;
String item ();
String assignedto ();
String Dateassigned ();
}
L Of course, the type of default value must be identical to the type of member variable declaration.
l The following is an example using the default value:
Public class testannotation {
@Inprocess
@Grouptodo
item = "Need to Finish this Method Later",
Assignedto = "Nelson_TU",
Dateassigned = "2005/02/05"
)
Public void test () {
}
}
l The following is an example of rewriting the default value:
Public class testannotation {
@Inprocess
@ TODO ("Need to Finish this Method Later")
@Grouptodo
Severity = grouptodo.severity.documentation,
item = "Need to Finish this Method Later",
Assignedto = "Nelson_TU",
Dateassigned = "2005/02/05"
)
Public void test () {
}
}
2, Yuan Annotation
L Yuan Annotation is Annotation's Annotation, JDK5 provides four predefined meta annotation (1) @target
l @Target Specifies the program element that can be applied to the Annotation type to make an ANNOTATION type in other program elements.
l The type of program element is defined by java.lang.annotation.ementType enumeration:
Package java.lang.annotation;
Public enum elementtype {
TYPE, // Class, Interface, or Enum (But not annotation)
Field, // Field (Including Enumerated Values)
Method, // Method (Does Not Include Construction ")
Parameter, // Method Parameter
Constructor, // Constructor
Local_variable, // local variable or catch clause
Annotation_Type, // annotation type (Meta-annotations)
Package // java package
}
l The following is an example of using @Target:
@Target ({ElementType.Type,
ElementType.method,
ElementType.constructor,
ElementType.annotation_type})
Public @Interface Todo {
String value ();
}
(2) @Retrion
L @ReTENTION and Java compiler processes the approach to annotation types
l These methods are defined by java.lang.annotation.RetentionPolicy enumeration:
Package java.lang.annotation;
Public enum restionpolicy {
Source, // annotation is discarded by the compiler
Class, // annotation is store, but ignore by the VM
Runtime // annotation is stored in the class file and read by the VM
}
l Use the @Retrion example to see the @Documented
(3) @document
l @documented indicates that you need ANNOTATION in Javadoc (the default is not included)
l The following is an example of using @Documented:
@Document
@ReTENTION (RETENTIONPOLICY.RUNTIME)
Public @Interface infrocess {
}
l A skill using @documented is to specify a retention policy to retectionPolicy.Runtime: This, Annotation will remain in the compiled class file and load it by virtual machine, then javadoc can extract Annotation, add to the HTML document Medium (4) @inherited
l @inherited is the most complicated, the least use of the most, and is most likely to confuse.
l Suppose using the @Inprogress tag a class that is being developed. As long as the @ Documented, Annotation information will appear in Javadoc; now you have to write a new class, expand the class being developed, then use the subclass, or view it. Documentation, there is no way to indicate where there is no completion; and it is hoping that the Annotation information of @Inprogress will be taken into the subclass, which requires @nnerited.
l The following example:
@Document
@Nnherited
@ReTENTION (RETENTIONPOLICY.RUNTIME)
Public @Interface infrocess {
}
