JAVA反射机制的本质是调用类的Class对象，通过操纵目标类Class对象来实现操纵目标对象

Class类对象是类装载器（ClassLoader）装载类之后，调用defineClass()生成的类的描述对象。
简单举例

package com.smart;

/**
 * @Author windy
 * @Desp
 * @Date 2019-07-29 20:43
 */
public class Car {

    private String brand;

    private String color;

    private int maxSpeed;

    public Car(){}

    public Car(String brand, String color, int maxSpeed){
        this.brand = brand;
        this.color = color;
        this.maxSpeed = maxSpeed;
    }

    public String getBrand() {
        return brand;
    }

    public void setBrand(String brand) {
        this.brand = brand;
    }

    public String getColor() {
        return color;
    }

    public void setColor(String color) {
        this.color = color;
    }

    public int getMaxSpeed() {
        return maxSpeed;
    }

    public void setMaxSpeed(int maxSpeed) {
        this.maxSpeed = maxSpeed;
    }

    @Override
    public String toString() {
        return "Car{" +
                "brand='" + brand + '\'' +
                ", color='" + color + '\'' +
                ", maxSpeed=" + maxSpeed +
                '}';
    }
}

测试类

package com.smart;

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

/**
 * @Author windy
 * @Desp
 * @Date 2019-07-29 20:45
 */
public class ReflectTest {

    public static Car initDefaultCar() throws Throwable {

        ClassLoader loader = Thread.currentThread().getContextClassLoader();
        Class clazz = loader.loadClass("com.smart.Car");

        Constructor cons =  clazz.getDeclaredConstructor();
        Car car = (Car) cons.newInstance();
        Method setBrand = clazz.getMethod("setBrand", String.class);
        setBrand.invoke(car, "大众");
        Method setColor = clazz.getMethod("setColor", String.class);
        setColor.invoke(car, "红色");
        Method setMaxSpeed = clazz.getMethod("setMaxSpeed", int.class);
        setMaxSpeed.invoke(car, 180);
        return car;
    }

    public static void main(String[] args) throws Throwable {
        System.out.println(initDefaultCar());
    }
}

获取当前线程的ContextClassLoader, 使用loadClass() 方法去加载指定类，生成Class对象，通过Class对象的描述信息，去获取 getDeclaredConstructor() 构造器，有了构造器 就可以初始化类了，这是间接的操纵这个类，通过 getMethod() 方法获取指定的方法，使用invoke() 方法调用该方法。当然了 也可以获取属性。