注解与反射机制：获取运行时类的完整结构

图1：

实现目标：test07获取test01的完整结构

test01 源代码：

package wanwan.pachage;
//什么叫反射
public class test01 extends Object{
    public static void main(String[] args) throws ClassNotFoundException {
        //通过反射获取类的class对象
        Class c1 = Class.forName("wanwan.pachage.test01.user");
        Class c2 = Class.forName("wanwan.pachage.test01.user");
        Class c3 = Class.forName("wanwan.pachage.test01.user");
        Class c4 = Class.forName("wanwan.pachage.test01.user");
        System.out.println(c1);
        //一个类在内存中只有一个class对象
        //一个类被加载后，类的整个结构都会封装在class对象中
        System.out.println(c2.hashCode());
        System.out.println(c3.hashCode());
        System.out.println(c4.hashCode());
    }

}
//实体类：pojo,entity
class user{
    private String name;
    private int age;
    private int id;
    public user() {
    }

    public user(String name, int age, int id) {
        this.name = name;
        this.age = age;
        this.id = id;
    }

    public String getName() {
        return name;
    }

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

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }

    public int getId() {
        return id;
    }

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

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

test07 源代码：

package wanwan.pachage;

import java.lang.reflect.Constructor;
import java.lang.reflect.Field;
import java.lang.reflect.Method;

public class test07 {
    public static void main(String[] args) throws ClassNotFoundException, NoSuchFieldException, NoSuchMethodException {
        Class c1 = Class.forName("wanwan.pachage.user");

        user u = new user();
        c1 = u.getClass();

        //获得类的名字
        System.out.println(c1.getName());//获得包名+类名
        System.out.println(c1.getSimpleName());//获得类名
        System.out.println("=======================");
        //获得类的属性
       Field[] fields = c1.getFields();//只能找到public属性
        /*for (Field field : fields) {
            System.out.println(field);
        }-----未能输出，why?--->属性私有
        */
        fields = c1.getDeclaredFields();//找到全部的属性
        for (Field field : fields) {
            System.out.println(field);
        }
        //获得指定属性的值
        /*
         Field name = c1.getField("name");//会报错，思考为什么？-->只能找到public属性
        System.out.println(name);
         */

        Field name = c1.getDeclaredField("name");
        System.out.println(name);
        //l获得类的方法
        System.out.println("============================");
        Method[] methods = c1.getMethods();//获得本类及父类的全部public方法
        for (Method method : methods) {
            System.out.println("正常的："+method);
        }
        System.out.println("============================");
        Method[] declaredMethods = c1.getDeclaredMethods();//获得本类的所有方法
        for (Method declaredMethod : declaredMethods) {
            System.out.println(declaredMethod);
        }
        System.out.println("==================================");
        //获得指定方法
        //重载
        Method getName = c1.getMethod("getName", null);
        Method setName = c1.getDeclaredMethod("setName", String.class);
        System.out.println(getName);
        System.out.println(setName);
        System.out.println("=========================");
        //获得指定的构造器
        Constructor[] constructors = c1.getConstructors();
        for (Constructor constructor : constructors) {
            System.out.println(constructor);
        }
       constructors=c1.getDeclaredConstructors();
        for (Constructor constructor : constructors) {
            System.out.println("###"+constructor);
        }
        //获得指定的构造器
        Constructor declaredConstructor = c1.getDeclaredConstructor(String.class, int.class, int.class);
        System.out.println("指定："+declaredConstructor);
    }
}

test07运行结果：

"C:\Program Files\Java\jdk1.8.0_221\bin\java.exe" "-javaagent:G:\IDEA\IntelliJ IDEA 2019.3.1\lib\idea_rt.jar=50156:G:\IDEA\IntelliJ IDEA 2019.3.1\bin" -Dfile.encoding=UTF-8 -classpath "C:\Program Files\Java\jdk1.8.0_221\jre\lib\charsets.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\deploy.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\access-bridge-64.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\cldrdata.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\dnsns.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\jaccess.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\jfxrt.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\localedata.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\nashorn.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\sunec.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\sunjce_provider.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\sunmscapi.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\sunpkcs11.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\zipfs.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\javaws.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\jce.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\jfr.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\jfxswt.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\jsse.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\management-agent.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\plugin.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\resources.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\rt.jar;E:\我的程序人生\java\Reflection\out\production\Reflection" wanwan.pachage.test07
wanwan.pachage.user
user
=======================
private java.lang.String wanwan.pachage.user.name
private int wanwan.pachage.user.age
private int wanwan.pachage.user.id
private java.lang.String wanwan.pachage.user.name
============================
正常的：public java.lang.String wanwan.pachage.user.toString()
正常的：public java.lang.String wanwan.pachage.user.getName()
正常的：public int wanwan.pachage.user.getId()
正常的：public void wanwan.pachage.user.setName(java.lang.String)
正常的：public int wanwan.pachage.user.getAge()
正常的：public void wanwan.pachage.user.setAge(int)
正常的：public void wanwan.pachage.user.setId(int)
正常的：public final void java.lang.Object.wait() throws java.lang.InterruptedException
正常的：public final void java.lang.Object.wait(long,int) throws java.lang.InterruptedException
正常的：public final native void java.lang.Object.wait(long) throws java.lang.InterruptedException
正常的：public boolean java.lang.Object.equals(java.lang.Object)
正常的：public native int java.lang.Object.hashCode()
正常的：public final native java.lang.Class java.lang.Object.getClass()
正常的：public final native void java.lang.Object.notify()
正常的：public final native void java.lang.Object.notifyAll()
============================
public java.lang.String wanwan.pachage.user.toString()
public java.lang.String wanwan.pachage.user.getName()
public int wanwan.pachage.user.getId()
public void wanwan.pachage.user.setName(java.lang.String)
public int wanwan.pachage.user.getAge()
public void wanwan.pachage.user.setAge(int)
public void wanwan.pachage.user.setId(int)
==================================
public java.lang.String wanwan.pachage.user.getName()
public void wanwan.pachage.user.setName(java.lang.String)
=========================
public wanwan.pachage.user()
public wanwan.pachage.user(java.lang.String,int,int)
###public wanwan.pachage.user()
###public wanwan.pachage.user(java.lang.String,int,int)
指定：public wanwan.pachage.user(java.lang.String,int,int)

Process finished with exit code 0