关于#java#的问题：请问String substring = "set"+key.substring(0,1).toUpperCase()+key.substring(1)

package com.daiyu;

import java.io.InputStream;
import java.lang.reflect.Method;
import java.util.Properties;
import java.util.Set;

/**
 *
 **/
public class A {
    public static void main(String[] args) throws Exception{
        //1.将conf.properties文件中的信息存到properties集合中
        Properties p = new Properties();
        InputStream inputStream = ClassLoader.getSystemClassLoader().getResourceAsStream("com/daiyu/conf.properties");
        p.load(inputStream);

        String className = p.getProperty("className");
        Class aClass = Class.forName(className);
        Object o = aClass.newInstance();

        Set set = p.stringPropertyNames();
        for (String key : set) {

            String substring = "set"+key.substring(0,1).toUpperCase()+key.substring(1);
            try {
                Method method = aClass.getMethod(substring,String.class);

                method.invoke(o,p.getProperty(key));
            } catch (NoSuchMethodException e) {
                //e.printStackTrace();
            }
        }
        System.out.println("通过配置文件创建了对象,并赋值结果是:"+o);
    }
}

#className=com.daiyu.Person
className=com.daiyu.User
username=zs
password=abc
name=ls
age=18

public class Person {
    private String name;
    private String age;

    @Override
    public String toString() {
        return "Person{" +
                "name='" + name + '\'' +
                ", age=" + age +
                '}';
    }
    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getAge() {
        return age;
    }

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


}

public class User {
    private String username;
    private String password;

    public String getUsername() {
        return username;
    }

    public void setUsername(String username) {
        this.username = username;
    }

    public String getPassword() {
        return password;
    }

    public void setPassword(String password) {
        this.password = password;
    }

    @Override
    public String toString() {
        return "User{" +
                "username='" + username + '\'' +
                ", password='" + password + '\'' +
                '}';
    }
}

请问String substring = "set"+key.substring(0,1).toUpperCase()+key.substring(1);什么意思

将key的首字母变成大写，这个主要是为了生成java bean 中字段对应的set方法名