gistfile1.txt

 class Person {

    private final String firstName; // required
    private final int age;
    private final String phone;

     private Person(PersonBuilder builder) {
        this.firstName = builder.firstName;
        this.age = builder.age;
        this.phone = builder.phone;
    }
    
    public String getFirstName() {
        return firstName;
    }

    public int getAge() {
        return age;
    }

    public String getPhone() {
        return phone;
    }

     @Override
     public String toString() {
         return "Person{" +
                 "firstName='" + firstName + '\'' +
                 ", age=" + age +
                 ", phone='" + phone + '\'' +
                 '}';
     }
     
     //Builder class
     public static class PersonBuilder
    {
        private final String firstName;
        private int age;
        private String phone;

        public PersonBuilder(String firstName) {
            this.firstName = firstName;
        }
        public PersonBuilder age(int age) {
            this.age = age;
            return this;
        }
        public PersonBuilder phone(String phone) {
            this.phone = phone;
            return this;
        }

        public Person build() {
            return new Person(this);
        }

    }

     public static void main(String[] args) {
         //Creating an Object
         Person person = new Person.PersonBuilder("Bhawna")
                 .age(23)
                 .phone("1234567")
                 .build();

         System.out.println(person);
         
     }
 }