如何使用java中的另一个类来更改类中变量的值？

public class Person {
    private String name;

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

public class Main {
    public static void main(String[] args) {
        Person person = new Person();
        person.setName("John");
    }
}

public class Person {
    private String name;

    public Person(String name) {
        this.name = name;
    }
}

public class Main {
    public static void main(String[] args) {
        Person person = new Person("John");
    }
}

public class Config {
    public static String name;

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

public class Main {
    public static void main(String[] args) {
        Config.setName("John");
    }
}