In the previous article, we explained: the definition of annotations in Java, JDK built-in notes, third-party comments.
This article is the second in series of tutorials comment. Take a look at the main contents of today:
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1: Classification annotated
2: a meta-annotation Description
3: custom annotation statement
I: Classification annotations
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NOTES Depending on the operating mechanism, origin, function points:
1.1: In accordance with the operating mechanism of points, there is immediate comment on what stage of the program
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Source notes (source): present in the source code.
Such as: lombak of @data notes:
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Compile notes (class): compile time. Both are in the source code and class.
JDK comes with three notes (@Override (rewrite covers), @ Deprecated (obsolete, outdated), @ Suppvisewarnings (compression warning)) is a compilation of comments
For example: override
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Run a comment (runtime): In the operational phase of any course work, and even affect the operation logic.
Such as: spring of autowired notes:
f39084e8c5e64a0834714f102eca9160.png1.2: According to the source to distinguish both notes come from
According to the source to differentiate into: JDK comes with notes, annotations third-party, custom annotations
As shown below:
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1.3: according to the function to distinguish between:
According to the function to distinguish, can be divided into: a meta-annotation and non-yuan notes. As shown below:
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II: Yuan notes explain
2.1: What is a meta-annotation?
Meta-annotation refers to the annotated notes. JAVA Ghost Notes includes the following four:
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2.2：@Target
target annotation functions: labeling annotation scope. If there are multiple scopes divided by commas
target annotation scope What?
Constructors, fields, local variables, methods, kits, parameters, interfaces. FIG follows:
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2.3：@Retention
The role of retention: the life cycle of annotations.
Notes life cycle, what does?
souce only in the source display, compile the class, the existence of run time runtime. As shown below:
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Lifecycle Size:
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2.4：@Inherited
inherite: identification of yuan notes. Identify the current annotation can be inherited by child comment
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2.5：@Documented
documented: at the time of document generation, will be included
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Three: custom annotation wording:
@Target({ElementType.METHOD, ElementType.FIELD})br/>@Retention(RetentionPolicy.RUNTIME)
@Inheritedbr/>@Documented()
public @interface MyAnnotation1 {
public abstract String value();}
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