初识反射 Java

Java学习笔记 初识反射

• 反射可以让程序更具有动态性

反射Api的简单使用

首先创建一个User类和一个TestClass类用来演示反射的动态加载，本篇笔记以代码为主

User

package com.bean;
public class User {
    private int id;
    private String userName;
    private int age;

    public User() {
    }

    public User(int id, String userName, int age) {
        this.id = id;
        this.userName = userName;
        this.age = age;
    }

    public int getId() {
        return id;
    }

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

    public String getUserName() {
        return userName;
    }

    public void setUserName(String userName) {
        this.userName = userName;
    }

    public int getAge() {
        return age;
    }

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

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

TestClass

import com.bean.User;

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

public class TestClass {
    public static void main(String[] args) {
       String path ="com.bean.User";
        try {
            Class clazz = Class.forName(path);
            //反射API获得所有的属性
            Field[] fileds = clazz.getDeclaredFields();
            System.out.println(Arrays.toString(fileds));
            //反射API获得所有的构造器，但构造器必须为公用的才能获取
            Constructor[] constructors = clazz.getConstructors();
            //向控制打印获得的构造器
            System.out.println(Arrays.toString(constructors));
            //反射API获得所有声明的构造器getDeclaredConstructors不局限于共有的构造器
            Constructor[] declaredConstructors = clazz.getDeclaredConstructors();
            //向控制打印获得的构造器
            System.out.println(Arrays.toString(declaredConstructors));
            //反射API获取无参构造器
            Constructor declaredConstructor = clazz.getDeclaredConstructor();
            //向控制打印获得的构造器
            System.out.println(declaredConstructor);
            //反射API获取有参构造器并实例化一个对象user打印在控制台上
            Constructor declaredConstructor1 = clazz.getDeclaredConstructor(int.class, String.class, int.class);
            User user= (User)declaredConstructor1.newInstance(1,"二狗",20);
            System.out.println(user);
            //反射API实例化一个user1对象
            User user1 =(User) clazz.newInstance();
            //反射API获得所有的方法
            Method[] mthtods = clazz.getDeclaredMethods();
            //打印所有的方法
            System.out.println(Arrays.toString(mthtods));
            //反射API为方法传输参数
            Method method = clazz.getDeclaredMethod("setUserName", String.class);
            method.invoke(user1,"张三");
            System.out.println(user1.getUserName());

            User user2=(User)clazz.newInstance();//实例化一个对象user2
            Field field = clazz.getDeclaredField("userName");//用反射API获得属性
            field.setAccessible(true);//告诉编译器不用进行安全检查
            field.set(user2,"李四");//给属性设置
            System.out.println(field.get(user2));//打印与下面的打印语句作用一样
            System.out.println(user2.getUserName());




        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}