BuilderPattern2.java

package builder;

public class User {
    private String firstName;
    private String lastName;
    private int age;
    private String email;

    private User(UserBuilder builder) {
        this.firstName = builder.firstName;
        this.lastName = builder.lastName;
        this.age = builder.age;
        this.email = builder.email;
    }

    @Override
    public String toString() {
        return "User: "+this.firstName+", "+this.lastName+", "+this.age+", "+this.email;
    }

    public static class UserBuilder {
        private final String firstName;
        private final String lastName;
        private int age;
        private String email;

        public UserBuilder(String firstName, String lastName) {
            this.firstName = firstName;
            this.lastName = lastName;
        }

        public UserBuilder age(int age) {
            this.age = age;
            return this;
        }

        public UserBuilder email(String email) {
            this.email = email;
            return this;
        }

        public User build() {
            User user = new User(this);
            return user;
        }
    }
}