第十四章 注解与反射

14.1 注解

User.java

enum User{
    LISI,JACK,MARY,ANDY,WANGWU
}

javac User.java 
User.class

class java
interface java
enum java
annotation java
module-info.java

class User{
    public void save(T t){
	
    }
}

User u = new User();
u.save(new Book());

User u = new User();
u.save(new Teacher());


List

泛型

枚举

注解  
comment 
annotation 
@Data

public enum RetentionPolicy {
    SOURCE,CLASS,RUNTIME
}

package cn.org;
import static java.lang.annotation.ElementType.*;
import java.lang.annotation.Documented;
import java.lang.annotation.Retention;
import static java.lang.annotation.RetentionPolicy.*;
import java.lang.annotation.Target;
/**
 * 
Project: part13 - Webrx
 * 
Powered By webrx
 * 
Created By IntelliJ IDEA On 2021-02-03 10:12:22
 * 
Description :
 *
 * @author webrx [webrx@126.com]
 * @version 1.0
 * @since 15
 */
@Documented
@Target({TYPE,FIELD,METHOD})
@Retention(RUNTIME) //RUNTIME > CLASS > SOURCE
public @interface Webrx {
    public String font() default "";
    public int age() default 25;
    public String[] values() default {"java","html","mysql"};
    public int pos() default 5;
}
/*
 * Copyright (c) 2006, 2021, webrx.cn All rights reserved.
 */
package cn.org;
/**
 * 
Project: part13 - MyUtil
 * 
Powered By webrx
 * 
Created By IntelliJ IDEA On 2021-02-03 11:01:27
 * 
Description :
 *
 * @author webrx [webrx@126.com]
 * @version 1.0
 * @since 15
 */
@Webrx(age=35,pos=9)
public class MyUtil {
    public void showAge(){
        //反射
        int a = this.getClass().getAnnotation(Webrx.class).age();
        System.out.println(a);
    }

    public static void main(String[] args) {
        MyUtil mu = new MyUtil();
        mu.showAge();
    }
}

14.2 反射

Java的反射（reflection）机制是指在程序的运行状态中，可以构造任意一个类的对象，可以了解任意一个对象所属的类，可以了解任意一个类的成员变量和方法，可以调用任意一个对象的属性和方法。这种动态获取程序信息以及动态调用对象的功能称为Java语言的反射机制。反射被视为动态语言的关键。

反射
Reflection
	User user = new User("b");
  2010 java java反射机制，打印出java.lang.String 的所有方法
        Class s = String.class;
        Class a = new String().getClass();
        Class c = Class.forName("java.lang.String");
        //Class
        //Method
        //Field
        System.out.println(a==c);
        //Arrays.stream(s.getDeclaredMethods()).forEach(e->System.out.println(e.getName()));
        Arrays.stream(s.getMethods()).forEach(e->System.out.println(e.getName()));

/*
 * Copyright (c) 2006, 2021, webrx.cn All rights reserved.
 *
 */
package cn.webrx.reflect;

import cn.org.Webrx;

/**
 * 
Project: part13 - Book
 * 
Powered By webrx
 * 
Created By IntelliJ IDEA On 2021-02-03 15:20:52
 * 
Description :
 *
 * @author webrx [webrx@126.com]
 * @version 1.0
 * @since 15
 */
@Webrx
public class Book {
    private int id;
    private String name;
    private double price;
    int i = 50;
    protected String user = "lisi";
    public String addr = "郑州市";

    public void info(){
        System.out.println("hello world info()...");
    }

    public Book() {
    }

    public Book(int id, String name, double price) {
        this.id = id;
        this.name = name;
        this.price = price;
    }

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public double getPrice() {
        return price;
    }

    public void setPrice(double price) {
        this.price = price;
    }

    @Override
    public String toString() {
        return "Book{" +
                "id=" + id +
                ", name='" + name + '\'' +
                ", price=" + price +
                '}';
    }
}

/*
 * Copyright (c) 2006, 2021, webrx.cn All rights reserved.
 *
 */
package cn.webrx.reflect;

import java.lang.reflect.Field;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.util.Arrays;

/**
 * 
Project: part13 - ReflectTest
 * 
Powered By webrx
 * 
Created By IntelliJ IDEA On 2021-02-03 15:20:46
 * 
Description :
 *
 * @author webrx [webrx@126.com]
 * @version 1.0
 * @since 15
 */
public class ReflectTest {
    public static void main(String[] args) throws ClassNotFoundException, NoSuchMethodException, IllegalAccessException, InvocationTargetException, InstantiationException, NoSuchFieldException {

        System.out.println(Class.forName("java.sql.Connection").isInterface());

        System.out.println(Integer.class.isPrimitive());

        //正常方式
        //var book = new Book();

        //反射方式 Class  Class
        var c1 = Book.class;
        String c = "cn.webrx.reflect.Book";

        var c2 = Class.forName(c);
        //System.out.println(c2.getName());//cn.webrx.reflect.Book
        //System.out.println(c2.getSimpleName());//Book

        //Method info = c2.getMethod("info");
        //System.out.println(info.invoke(c2.getConstructor().newInstance()));

        Arrays.stream(c2.getDeclaredFields()).forEach(e->{
            System.out.println(e.getName());
        });

        Field fi = c2.getDeclaredField("i");
        System.out.println(fi.getType());

        System.out.println(fi.get(c2.getConstructor().newInstance()));

        //0 1 2 3 4
        System.out.println(c2.getDeclaredField("id").getModifiers());
        System.out.println(c2.getDeclaredField("i").getModifiers());
        System.out.println(c2.getDeclaredField("user").getModifiers());
        System.out.println(c2.getDeclaredField("addr").getModifiers());

        //var c3 = book.getClass();
        //System.out.println(c1.hashCode());
        //System.out.println(c2.hashCode());
        //System.out.println(c3.hashCode());

        //通过反射来实现对象
        //Book bk = (Book)c2.getDeclaredConstructors()[0].newInstance(3,"java",40d);
        //bk.info();
        //System.out.println(bk);



        var c4 = String.class;
        var c5 = int[][].class;
        var c6 = Class.class;
        var c7 = void.class;
        var c8 = Object.class;
        var c9 = String[][][].class;

    }
}