Builder with mandatory fields, compile time safe

validbuilder.java

package com.example.demo.model;

import java.util.concurrent.atomic.AtomicInteger;

public class Builder {
  
      public static void main(String[] args) {

        ValidUser validUser =  new Builder().builder()
                .name("name")
                .age(12)
                .build();

    }
  
    private String name;
    private AtomicInteger age;
    private NameSetter nameSetter;
    
    public Builder builder() {
        this.name = "";
        this.age = new AtomicInteger();
        AgeSetter ageSetter = new AgeSetter(this, age);
        this.nameSetter = new NameSetter(ageSetter);
        return this;
    }

    public AgeSetter name(String name) {
        this.name = name;

        return this.nameSetter.getAgeSetter();
    }

    public ValidUser build() {
        return new ValidUser(this.name, this.age);
    }

    public static class NameSetter {
        private final AgeSetter ageSetter;

        public NameSetter(AgeSetter ageSetter) {
            this.ageSetter = ageSetter;
        }

        public AgeSetter getAgeSetter() {
            return ageSetter;
        }
    }

    public static class AgeSetter {
        private final Builder builder;
        private final AtomicInteger age;

        public AgeSetter(Builder builder, AtomicInteger age) {
            this.builder = builder;
            this.age = age;
        }

        public Builder age(int age) {
            this.age.set(age);
            return this.builder;
        }

    }

}