什么是java反射

import java.lang.reflect.Constructor;
//用来演示构造函数的使用
public class CreateObject {
    public void useConstructor() {
        try {
            //获取Student的字节流对象
            Class studentClass = Class.forName("Student");
            System.out.println("开始调用Student无参构造函数");
            //---------------构造函数的访问------------------
            //创建对象，无参构造函数
            Object obj = studentClass.newInstance();
            //转化成我们要使用的对象
            Student student2 = (Student) obj;
            student2.study();
            System.out.println("结束调用Student无参构造函数");
            System.out.println("开始调用Student公有带参构造函数");
            //反射的getConstructor方法的使用，公有带参构造函数
            Constructor<?> constructor = studentClass.getConstructor(int.class, String.class);
            Object obj2 = constructor.newInstance(12, "23");
            Student stu2 = (Student) obj2;
            stu2.study();
            System.out.println("结束调用Student公有带参构造函数");
            System.out.println("开始调用Student私有带参构造函数");
            //getDeclaredConstructor方法的使用，私有带参构造函数
            Constructor<?> constructor2 = studentClass.getDeclaredConstructor(int.class);
            //设置私有构造函数可访问
            constructor2.setAccessible(true);
            Object obj3 = constructor2.newInstance(12);
            Student stu3 = (Student) obj3;
            stu3.study();
            System.out.println("结束调用Student私有带参构造函数");
        } catch (Exception e) {
            System.out.println(e);
        }
    }
}

import java.lang.reflect.Field;
import java.lang.reflect.Method;
//用来演示方法的使用
public class UseMethod {
    public void useMethod(){
        try {
            //获取Student的字节流对象
            Class<Student> stuClass = (Class<Student>) Class.forName("Student");
            //公有方法,且不传参
            Student student = stuClass.newInstance();
            Method study = stuClass.getMethod("study");
            //调用公有学习方法
            System.out.println("调用了公有的study方法");
            study.invoke(student);
            //私有方法
            Student student2 = stuClass.newInstance();
            Method sayHi = stuClass.getDeclaredMethod("sayHi",String.class);
            sayHi.setAccessible(true);
            System.out.println("调用了私有的sayHi方法");
            //通过invoke调用sayHi
            sayHi.invoke(student2, "Tony");
        } catch (Exception e) {
            System.out.println(e);
        }
    }
}

import java.lang.reflect.Constructor;
import java.lang.reflect.Field;
//用来演示属性的使用
public class UseAttribute {
    public void useAttribute() {
        try {
            //获取Student的字节流对象
            Class<Student> stuClass = (Class<Student>) Class.forName("Student");
            //公有属性
             Student student = stuClass.newInstance();
             Field score = stuClass.getField("score");
             score.set(student, 12);
           //私有属性
            Student student2 = stuClass.newInstance();
            Field age = stuClass.getDeclaredField("age");
            age.setAccessible(true);
            age.set(student2, 12);
            //获取所有属性
            for (Field field : stuClass.getFields()) {
                System.out.println(field);
            }
            System.out.println("---分割线---");
            for (Field declaredField : stuClass.getDeclaredFields()) {
                System.out.println(declaredField);
            }
        } catch (Exception e) {
            System.out.println(e);
        }
    }
}

public class Client {
    //程序入口
    public static void main(String[] args) {
        //调用三种类型的构造函数
        CreateObject createObject1 = new CreateObject();
        createObject1.useConstructor();
        //调用两种不同类型的方法
       UseMethod useMethod1 = new UseMethod();
       useMethod1.useMethod();
        //调用两种不同的属性
        UseAttribute useAttribute1 = new UseAttribute();
        useAttribute1.useAttribute();
    }
}