Java meta Annotations, simple cases

• • Annotations

The program has Notes and Annotations

* Note: For developers .

* Note: to the computer to see .

Annotations Use: The Learning Framework supports annotation development .

• • " The notes provided by the JDK "

@Override : Describes the override of the method .

@SuppressWarnings : Suppress the warning .

@Deprecated : Markup is obsolete .

• • Custom annotations:

define a class : Class

define an excuse : interface

define an enumeration : enum

define an annotation : @interface

Usage:

　

@Interfacemyanno1{} Annotated with attributes: @Interfacemyanno2{intA ()default1;    String b (); //the type of the annotation property: the base data type, the string type String,class, the annotation type, the enumeration type, and the one-dimensional array of the above types. //Date D ();Class clazz (); MyAnno3 m3 (); //AnnotationsColor c ();//Enumerationstring[] Arrs (); } @MyAnno4 ("AAA")//If the property name is value then value can be omitted (only if the property of this value is present). Public classAnnotationDemo3 {}@Interfacemyanno4{String value (); intA ()default1;}

　

"Custom Annotation Cases"

Annotation class

1  Packagecom.xujingyang.annotation;2 3 ImportJava.lang.annotation.ElementType;4 Importjava.lang.annotation.Retention;5 ImportJava.lang.annotation.RetentionPolicy;6 ImportJava.lang.annotation.Target;7 8 //keep to run time9 @Retention (retentionpolicy.runtime)Ten //can only act on the method One @Target (Elementtype.method) A  Public@InterfaceMyTest { -      -}

Test Note class

1  Packagecom.xujingyang.annotation;2 3  Public classTest {4 @MyTest5      Public voidF1 () {6System.out.println ("F1 method executed ~ ~ ~ ~ ~");7     }8     9      Public voidF2 () {TenSystem.out.println ("F2 method executed ~ ~ ~ ~ ~"); One     } A      - @MyTest -      Public voidF3 () { theSystem.out.println ("F3 method executed ~ ~ ~ ~ ~"); -     } -}

Main test class

1  Packagecom.xujingyang.annotation;2 3 ImportJava.lang.reflect.Method;4 5  Public classMain {6      Public Static voidMain (string[] args)throwsexception{7Class Clazz=test.class;8         9Method[] Methods =clazz.getmethods ();Ten          for(Method method:methods) { One //Method.invoke (Clazz.newinstance ()); A //System.out.println (Method.getname ()); -             Booleanb = Method.isannotationpresent (MyTest.class);//determine if you have added this annotation -             if(b) { the Method.invoke (Clazz.newinstance ()); -             } -         } -     } +}

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Case two, using annotations to load parameters to get JDBC connections

Annotation class

1  PackageCom.xujingyang.jdbc;2 3 ImportJava.lang.annotation.ElementType;4 Importjava.lang.annotation.Retention;5 ImportJava.lang.annotation.RetentionPolicy;6 ImportJava.lang.annotation.Target;7 //keep to run time8 @Retention (retentionpolicy.runtime)9 //This annotation can only be added on a methodTen @Target (Elementtype.method) One  Public@InterfaceJdbcinfo { A     //defines several properties for loading a database, which can be assigned defaults with the default keyword -String Driverclass ()default"Com.mysql.jdbc.Driver"; - String Url (); theString User ()default"Root"; -String PWD ()default"Root"; -}

Test class

1  PackageCom.xujingyang.jdbc;2 3 ImportJava.lang.reflect.Method;4 Importjava.sql.Connection;5 ImportJava.sql.DriverManager;6 7  Public classConn {8      Public Static voidMain (string[] args)throwsException {9System.out.println (getconnection ());//Print connection address, indicating successTen     } One      A@JDBCInfo (url= "JDBC:MYSQL://LOCALHOST:3306/DAY16") -      Public StaticConnection getconnection ()throwsexception{ -         //to load a byte-code object for a class theClass<conn> Clazz=conn.class; -          -         //Get This method -method = Clazz.getmethod ("getconnection"); +          -         //Get Annotation Object +Jdbcinfo info = method.getannotation (jdbcinfo.class); A          at         //get the properties of each assigned value -String Driverclass =info. Driverclass (); -String URL =info. Url (); -String user =info. User (); -String pwd =info. PWD (); -          in         //Registration Driver - Class.forName (driverclass); to          +         //Get Connected -         returndrivermanager.getconnection (URL, user, pwd); the     } *}

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The simple use of annotations is so much to remember that more in-depth research will be done later

Java meta Annotations, simple cases