JavaSE-24.2.5【反射案例-越过泛型检查、运行配置文件中指定类的指定方法】

package day15.lesson2.p;

import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.util.ArrayList;

/*
2.10 反射练习

2.10.1 案例-越过泛型检查
    通过反射技术，向一个泛型为Integer的ArrayList集合中添加一些字符串String数据
 */
public class Test1Reflect {
    public static void main(String[] args) throws NoSuchMethodException, InvocationTargetException, IllegalAccessException {
        ArrayList<Integer> arrayList = new ArrayList<>();

        arrayList.add(10);
        arrayList.add(20);
//        arrayList.add("hello"); //报错，编译异常 --> 即正常情况下无法在ArrayList<Integer>中添加String数据

        //通过反射可以实现该功能
        Class<? extends ArrayList> c = arrayList.getClass();
        Method add = c.getMethod("add", Object.class); //类型为Object-->那么通过反射在arrayList添加啥类型数据都行了QAQ
        //反射可以越过泛型检查，获取到原始方法所需的参数类型
        add.invoke(arrayList, "hello");
        add.invoke(arrayList, "world");
        add.invoke(arrayList, "java");

        System.out.println(arrayList); //[10, 20, hello, world, java]
    }
}

package day15.lesson2.p;

public class Student {
    public void study(){
        System.out.println("好好学习天天向上");
    }
}

package day15.lesson2.p;

public class Teacher {
    public void teach(){
        System.out.println("好好教书");
    }
}

package day15.lesson2.p;

import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.IOException;
import java.lang.reflect.Constructor;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.util.Properties;

/*
2.10.2 案例-运行配置文件中指定类的指定方法
 */
public class Test2Reflect {
    public static void main(String[] args) throws IOException, ClassNotFoundException, NoSuchMethodException, IllegalAccessException, InstantiationException, InvocationTargetException {
        /*Student student = new Student();
        student.study(); //好好学习天天向上
        Teacher teacher = new Teacher();
        teacher.teach(); //好好教书*/

        /*
        自定义配置文件
        class.txt
            className=xxx  (注意此处类名应为带包全路径)
            methodName=xxx
         */
        Properties properties = new Properties();
        FileReader fr = new FileReader("stage2\\src\\day15\\lesson2\\p\\class.txt");
        properties.load(fr);
        fr.close();
        System.out.println(properties); //{methodName=study, className=day15.lesson2.p.Student}

        String className = properties.getProperty("className");
        String methodName = properties.getProperty("methodName");
        System.out.println(className + "," + methodName); //day15.lesson2.p.Student,study

        //通过反射使用 从配置文件中获取的配置信息
        Class<?> c = Class.forName(className);
        Constructor<?> con = c.getConstructor();
        Object obj = c.newInstance();
        Method method = c.getMethod(methodName);
        method.invoke(obj);
        /*
        className=day15.lesson2.p.Student
        methodName=study
        --> 好好学习天天向上

        className=day15.lesson2.p.Teacher
        methodName=teach
        --> 好好教书
         */
    }
}

className=day15.lesson2.p.Teacher
methodName=teach