Builder pattern is useful to dinamically create classes, separating the construction of a complex object.

For example, let's say we want to create a crew member of a spaceship. It's a role that demands a lot of responsability, and many documents are necessary to register a crew member:

• id
• name
• species
• rank
• serialNumber
• status
• birthDate
• bloodType

It would be annoying and difficult to understand having all these attributes in a single constructor:

public CrewMember(Integer id, String name, Specie specie, Rank rank, String serialNumber, Status status, Date birthDate, BloodType bloodType);

and the creation would be:

CrewMember crewMember = new CrewMember(1, "Kirk", Specie.HUMAN, Rank.CAPTAIN, "SC937-0176CEC", Status.DECEASED, LocalDate.of(2233, 3, 22), BloodType.AB);

witch is hard to understand what each part is, and is important to keep everything in the same place implemented by the constructor.

Creating a complex object gets easier by dividing the process in parts

CrewMember crewMember = crewMemberBuilder.setName("Spok").setspecie(Specie.VULCANO).setRank(Rank.COMMANDER)
                                         .setSerialNumber("S 179-276 SP").setStatus(Status.MISSING)
                                         .setBirthDate(LocalDate.of(2285, 1, 6)).setBloodType(BloodType.T).build();

witch is better to read and understand, and the order of the steps doesn't matter.