关于反射机制的简单理解

/**
 * Created with IntelliJ IDEA.
 * Description:
 * User: GAOBO
 * Date: 2020-02-20
 * Time: 15:24
 */
class Student{
    //私有属性name
    private String name = "smallye";
    //公有属性age
    public int age = 18;
    //不带参数的构造方法
    public Student(){
        System.out.println("Student()");
    }
    private Student(String name,int age) {
        this.name = name;
        this.age = age;
        System.out.println("Student(String,name)");
    }
    private void eat(){
        System.out.println("i am eat");
    }
    public void sleep(){
        System.out.println("i am pig");
    }
    private void function(String str) {
        System.out.println(str);
    } @
            Override
    public String toString() {
        return "Student{" +
                "name='" + name + '\'' +
                ", age=" + age +
                '}';
    }
}
public class TestDemo {
    public static void main(String[] args) {

        /*
        1.通过getClass获取Class对象
        */

        Student s1 = new Student();
        Class c1 = s1.getClass();

         /*
         2.直接通过 类名.class 的方式得到,该方法最为安全可靠，程序性能更高
        这说明任何一个类都有一个隐含的静态成员变量 class
        */

        Class c2 = Student.class;

        /*
        3、通过 Class 对象的 forName() 静态方法来获取，用的最多，
        但可能抛出 ClassNotFoundException 异常
        */

        Class c3 = null;
        try {
            //注意这里是类的全路径，如果有包需要加包的路径
            c3 = Class.forName("Student");
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        }

        //一个类在 JVM 中只会有一个 Class 实例,即我们对上面获取的
        //c1,c2,c3进行 equals 比较，发现都是true
        System.out.println(c1.equals(c2));
        System.out.println(c1.equals(c3));
        System.out.println(c2.equals(c3));
    }
}

package demo1;

import demo1.Student;

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

public class ReflectClassDemo {
    // 创建对象
    public static void reflectNewInstance() {
        try {
            Class<?> classStudent = Class.forName("demo1.Student");
            Object objectStudent = classStudent.newInstance();
            Student student = (Student) objectStudent;
            System.out.println("获得学生对象："+student);
        } catch (Exception ex) {
            ex.printStackTrace();
        }
    }
    // 反射私有的构造方法 屏蔽内容为获得公有的构造方法
    public static void reflectPrivateConstructor() {
        try {
            Class<?> classStudent = Class.forName("demo1.Student");
//注意传入对应的参数
            Constructor<?> declaredConstructorStudent = classStudent.getDeclaredConstructor(String.class,int.class);
//Constructor<?> declaredConstructorStudent = classStudent.getConstructor();
//设置为true后可修改访问权限
            declaredConstructorStudent.setAccessible(true);
            Object objectStudent = declaredConstructorStudent.newInstance("萨摩耶",15);
//Object objectStudent = declaredConstructorStudent.newInstance();
            Student student = (Student) objectStudent;
            System.out.println("获得私有构造函数且修改姓名和年龄："+student);
        } catch (Exception ex) {
            ex.printStackTrace();
        }
    }
    // 反射私有属性
    public static void reflectPrivateField() {
        try {
            Class<?> classStudent = Class.forName("demo1.Student");
            Field field = classStudent.getDeclaredField("name");
            field.setAccessible(true);
//可以修改该属性的值
            Object objectStudent = classStudent.newInstance();
            Student student = (Student) objectStudent;
            field.set(student,"石瑞泽");
            String name = (String) field.get(student);
            System.out.println("反射私有属性修改了name："+ name);
        } catch (Exception ex) {
            ex.printStackTrace();
        }
    }
    // 反射私有方法
    public static void reflectPrivateMethod() {
        try {
            Class<?> classStudent = Class.forName("demo1.Student");
            Method methodStudent = classStudent.getDeclaredMethod("function",String.class);
            System.out.println("私有方法的方法名为："+methodStudent.getName());
//私有的一般都要加
            methodStudent.setAccessible(true);
            Object objectStudent = classStudent.newInstance();
            Student student = (Student) objectStudent;
            methodStudent.invoke(student,"我是给私有的function函数传的参数");
        } catch (Exception ex) {
            ex.printStackTrace();
        }
    }
    public static void main(String[] args) {
        reflectNewInstance();
        reflectPrivateConstructor();
        reflectPrivateField();
        reflectPrivateMethod();
    }
}