Exception in thread “main“ java.lang.IllegalAccessException

package com.fan.reflect;

import com.fan.model.User;
import java.lang.reflect.Field;

public class 根据属性名获得属性对象并调用该属性 {
    public static void main(String[] args) throws NoSuchFieldException, InstantiationException, IllegalAccessException {
        Class userClass = User.class;
        //根据属性名获得一个属性对象
        Field field = userClass.getDeclaredField("user_name");
        
        //通过Class创建类的对象,该方法调用类的无参数的构造方法创建类的实例
        User user = userClass.newInstance();
        field.set(user,"樊军刚");//设置属性的值
        String val= (String) field.get(user);
        System.out.println(val);


    }
}

package com.fan.model;
public class User {
    private  Integer  user_id;
    private   String  user_name;
    private  String  user_password;

    public User(Integer user_id, String user_name, String user_password) {
        this.user_id = user_id;
        this.user_name = user_name;
        this.user_password = user_password;
    }

    public User() {
    }

    public Integer getUser_id() {
        return user_id;
    }

    public void setUser_id(Integer user_id) {
        this.user_id = user_id;
    }

    public String getUser_name() {
        return user_name;
    }

    public void setUser_name(String user_name) {
        this.user_name = user_name;
    }

    public String getUser_password() {
        return user_password;
    }

    public void setUser_password(String user_password) {
        this.user_password = user_password;
    }

    @Override
    public String toString() {
        return "User{" +
                "user_id=" + user_id +
                ", user_name='" + user_name + ''' +
                ", user_password='" + user_password + ''' +
                '}';
    }
}

我是想通过反射给User_name属性赋值,我是根据属性名获得属性对象,然后通过反射创建该对象,并给该对象赋值,但是有问题,出现了以下的bug

Exception in thread "main" java.lang.IllegalAccessException: Class com.fan.reflect.根据属性名获得属性对象并调用该属性 can not access a member of class com.fan.model.User with modifiers "private"
	at sun.reflect.Reflection.ensureMemberAccess(Reflection.java:102)
	at java.lang.reflect.AccessibleObject.slowCheckMemberAccess(AccessibleObject.java:296)
	at java.lang.reflect.AccessibleObject.checkAccess(AccessibleObject.java:288)
	at java.lang.reflect.Field.set(Field.java:761)
	at com.fan.reflect.根据属性名获得属性对象并调用该属性.main(根据属性名获得属性对象并调用该属性.java:27)

后来发现是自己User中的那个Use_name属性修饰符为private
然后就好了,结果:

D:jdk8u301binjava.exe "-javaagent:D:IntelliJ IDEA 2021.3.2libidea_rt.jar=9086:D:IntelliJ IDEA 2021.3.2bin" -Dfile.encoding=UTF-8 -classpath D:jdk8u301jrelibcharsets.jar;D:jdk8u301jrelibdeploy.jar;D:jdk8u301jrelibextaccess-bridge-64.jar;D:jdk8u301jrelibextcldrdata.jar;D:jdk8u301jrelibextdnsns.jar;D:jdk8u301jrelibextjaccess.jar;D:jdk8u301jrelibextjfxrt.jar;D:jdk8u301jrelibextlocaledata.jar;D:jdk8u301jrelibextnashorn.jar;D:jdk8u301jrelibextsunec.jar;D:jdk8u301jrelibextsunjce_provider.jar;D:jdk8u301jrelibextsunmscapi.jar;D:jdk8u301jrelibextsunpkcs11.jar;D:jdk8u301jrelibextzipfs.jar;D:jdk8u301jrelibjavaws.jar;D:jdk8u301jrelibjce.jar;D:jdk8u301jrelibjfr.jar;D:jdk8u301jrelibjfxswt.jar;D:jdk8u301jrelibjsse.jar;D:jdk8u301jrelibmanagement-agent.jar;D:jdk8u301jrelibplugin.jar;D:jdk8u301jrelibresources.jar;D:jdk8u301jrelibrt.jar;D:ideaprojectsuser_systargetclasses;D:Mavenapache-maven-3.8.4Maven-repoorgapachetaglibstaglibs-standard-compat1.2.5taglibs-standard-compat-1.2.5.jar;D:Mavenapache-maven-3.8.4Maven-repoorgapachetaglibstaglibs-standard-spec1.2.5taglibs-standard-spec-1.2.5.jar;D:Mavenapache-maven-3.8.4Maven-repoorgapachetaglibstaglibs-standard-impl1.2.5taglibs-standard-impl-1.2.5.jar;D:Mavenapache-maven-3.8.4Maven-repomysqlmysql-connector-java8.0.26mysql-connector-java-8.0.26.jar;D:Mavenapache-maven-3.8.4Maven-repocomgoogleprotobufprotobuf-java3.11.4protobuf-java-3.11.4.jar com.fan.reflect.根据属性名获得属性对象并调用该属性
樊军刚

进程已结束,退出代码0

自己有对那个user_name属性的修饰符进行了实验,分别用public ,private,默认,protected,得出一下结论
结论:
说明通过反射创建的对象,调用set给属性赋值,属性不能是private,protected,默认,只有public才可以