Annotation and reflection

One ： annotation

Custom annotation ：

import java.lang.annotation.*;

/** *  Built-in annotations  * @Override  Representation override  * @Deprecated  Indicates that it has been deprecated  * @SuppressWarnings  Indicates no warning  */

/** *  Yuan notes - Custom annotation  * @author liu ming yong */
@MyAnnotation(value = " Custom annotation ")
public class Annotation {
    
    //  Note if the parameter has no default value , Then the annotation must be assigned 
    @MyAnnotation(value = "qq")
    public void s(){
    

    }

}

/** * @Target  Indicates where annotations can be used  TYPE( class ),METHOD( Method ) * @Retention  Indicates where the annotation is valid  runtime( Runtime )>class( Compiled bytecode )>sources( Source code ) * @Documented  Indicates whether the annotation is produced in JAVAdoc in  * @Inherited  Indicates that the child class can inherit the parent class annotation  * @author liu ming yong */
@Target(value = {
    ElementType.TYPE,ElementType.METHOD})
@Retention(value = RetentionPolicy.RUNTIME)
@Documented
@Inherited
@interface MyAnnotation {
    
    //  Annotated parameters ： Parameter type   Parameter name ();
    String value();
    String name() default "my name is liu ming yong";
    int age() default 0;
    String[] schools() default {
    " National Defense University "," Tsinghua University "};
}

Two ： Reflection

The concept of reflection ：
Reflection( Reflection ) yes java It is regarded as a quasi dynamic language ( A language that can change its structure during operation ) The key to , Reflection allows the program to get the internal information of any class during execution , And can directly operate the internal properties or methods of any object .
After class loading , In the heap memory method area, a Class Type object ( There is only one class Class object ), This object contains the complete class structure information .
Get reflection Class In several ways ：

/** * @author liu ming yong */
public class Reflection01 {
    
    public static void main(String[] args) throws ClassNotFoundException {
    
        Person person = new Student();
        //  Mode one : Get... By object 
        Class c1 = person.getClass();
        System.out.println(c1);
        //  Mode two : adopt forName get 
        Class c2 = Class.forName(" Comments and reflections .Student");
        System.out.println(c2);
        //  Mode three : By class name .class get 
        Class c3 = Student.class;
        System.out.println(c3);
        //  Mode 4 : Get through the wrapper class of basic data type 
        Class c4 = Integer.TYPE;
        System.out.println(c4);
        //  Get parent type 
        Class c5 = c1.getSuperclass();
        System.out.println(c5);

    }
}

class Person {
    
    String name;

    public Person() {
    
    }

    public Person(String name) {
    
        this.name = name;
    }

    @Override
    public String toString() {
    
        return "Person{" +
                "name='" + name + '\'' +
                '}';
    }
}

class Student extends Person {
    

}

Get the structure of the class runtime ：