Java USES reflection to get the class attribute value of the implementation code

How it works: reflection in Java can get the name of the property and then invoke a method of the class.
For example, if you have a property called userName, and this class writes a method called getUserName, call the getUserName method by invoking.
The following code

import java.lang.reflect.Field;
import java.lang.reflect.Method;
import java.util.HashMap;
import java.util.Map;
public class ParameterBase
{
    
    public Map<String, String> getClassInfo()
    {
        Map<String ,String>  fieldsAndValues = new HashMap<String, String>();
        Field [] fields = this.getClass().getDeclaredFields();
        for(int i=0; i< fields.length; i++)
        {
            Field f = fields[i];
            String value = getFieldValue(this ,f.getName()).toString();
            fieldsAndValues.put(f.getName(),value);
        } 
      return fieldsAndValues;
    }  

    

    private  String getFieldValue(Object owner, String fieldName)
    {
        return invokeMethod(owner, fieldName,null).toString();
    }

    
    
    private   Object invokeMethod(Object owner, String fieldName, Object[] args)
    {
        Class<? extends Object> ownerClass = owner.getClass();

        //fieldName -> FieldName  
        String methodName = fieldName.substring(0, 1).toUpperCase()+ fieldName.substring(1);

        Method method = null;
        try 
        {
            method = ownerClass.getMethod("get" + methodName);
        } 
        catch (SecurityException e) 
        {
            //e.printStackTrace();
        } 
        catch (NoSuchMethodException e) 
        {
            // e.printStackTrace();
            return "";
        }

        //invoke getMethod
        try
        {
            return method.invoke(owner);
        } 
        catch (Exception e)
        {
            return "";
        }
    }
}

Write a class User inherited from ParameterBase and write a test code

public class User extends ParameterBase
{
    String userName ;
    String passWorld;
    public String getUserName()
    {
        return userName;
    }
    public void setUserName(String userName)
    {
        this.userName = userName;
    }
    public String getPassWorld()
    {
        return passWorld;
    }
    public void setPassWorld(String passWorld)
    {
        this.passWorld = passWorld;
    }

    public static void main(String[] args)
    {
        User u = new  User();
        u.passWorld = "123";
        u.userName = "aaaaa";
        System.out.println(u.getClassInfo().toString());

    }
}

Program output

{passWorld=123, userName=aaaaa}