005-java's annotation

I. Overview

annotation,jdk1.5 started offering

II. Basic Definitions

 public @Interface  HelloWorld {}

1, use @interface definition, name capital

2, the use of @target decoration can be placed on those class attributes, do not write is able to modify any Java

3, meta-annotations Retentionpolicy, indicating the life cycle of annotations:

1, SOURCE: In the original file is valid, is discarded by the compiler.
2, Class: In the class file is valid, may be ignored by the virtual machine.
3. Runtime: Valid at run time.

4, members, defined in the annotations "cannot be class type, object type, etc., but class can"

 Public String name ();

Add default value

 Public default "HelloWorld";

If there is only one member and is value, you can omit it and write the value directly when you use it.

5. Use

@HelloWorld (name = "Nihao1")publicclass  Testbean {    = "Nihao2")     Private  String name;    @Override    = "Nihao3")    public  String toString () {
System.out.println ("zhixing");         return this. Name + "]";    }}

Iii. main role

1, for the above do not do any processing actually no use

2, parse annotation, and then deal with the problem

 Public classParser { Public voidParse (Object obj, String methodName) {method[] Ms=Obj.getclass (). GetMethods ();  for(Method m:ms) {if(M.getname (). Equals (MethodName)) {if(M.isannotationpresent (HelloWorld.class) ) {HelloWorld HW= M.getannotation (HelloWorld.class); Try{System.out.println ("Before ..."); M.invoke (obj,NULL); System.out.println ("After ..."); } Catch(Exception e) {//TODO auto-generated Catch blockE.printstacktrace (); }                }            }        }    }}

3, the main method of annotation treatment

4, can replace the XML configuration

005-java's annotation