Achieving Immutability with Builder Design Pattern

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Immutable User

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01.public class ImmutableUser {

02. 

03.private final String username;

04.private final String password;

05.private final String firstname;

06.private final String lastname;

07.private final String email;

08.private final Date creationDate;

09. 

10.private ImmutableUser(UserBuilder builder) {

11.this.username = builder.username;

12.this.password = builder.password;

13.this.creationDate = builder.creationDate;

14.this.firstname = builder.firstname;

15.this.lastname = builder.lastname;

16.this.email = builder.email;

17.}

18. 

19.public static class UserBuilder {

20.private final String username;

21.private final String password;

22.private final Date creationDate;

23.private String firstname;

24.private String lastname;

25.private String email;

26. 

27.public UserBuilder(String username, String password) {

28.this.username = username;

29.this.password = password;

30.this.creationDate = new Date();

31.}

32. 

33.public UserBuilder firstName(String firsname) {

34.this.firstname = firsname;

35.return this;

36.}

37. 

38.public UserBuilder lastName(String lastname) {

39.this.lastname = lastname;

40.return this;

41.}

42. 

43.public UserBuilder email(String email) {

44.this.email = email;

45.return this;

46.}

47. 

48.public ImmutableUser build() {

49.return new ImmutableUser(this);

50.}

51. 

52.}

53. 

54.public String getUsername() {

55.return username;

56.}

57. 

58.public String getPassword() {

59.return password;

60.}

61. 

62.public String getFirstname() {

63.return firstname;

64.}

65. 

66.public String getLastname() {

67.return lastname;

68.}

69. 

70.public String getEmail() {

71.return email;

72.}

73. 

74.public Date getCreationDate() {

75.return new Date(creationDate.getTime());

76.}

77. 

78.}

 

You should also check the invariants in the build method and throw in an IllegalStateException if any attribute is invalid. This will ensure that the object is in a workable state once it is instantiated.

The client code will look like this :

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1.public static void main(String[] args) {

2.ImmutableUser user = new ImmutableUser.UserBuilder("shekhar",

3."password").firstName("shekhar").lastName("gulati")

4..email("shekhargulati84@gmail.com").build();

5.}