The theme of this workshop is to learn the latest Java features, with an emphasis on picking up a couple of paradigms along the way - namely Functional Reactive Programming and how this fits in with the latest Java releases.

1. F U N C T I O N A L - R E A C T I V E
@ S V E N R U P P E R T
5
S T O R Y A N D P H I L O S O P H Y
Software is eating the world and what most of us see of it is the user interface. The user
interface has become the key component of how the users experience the business
behind it. Competition is lost or won due to user experience. Simplicity is king and the
users get frustrated by anything ugly, slow or not working on the device they happen to
use at the time. We at Vaadin fight for simplicity and invite everyone to join this fight.
Together we want to build a user interface that puts a smile on the user’s face.
Vaadin is the technology that empowers developers to build the best web-apps for
business purposes. Our priority over everything else is developer productivity because
we believe that by simplifying the developer experience and saving the developer’s
time, they are best able to focus on building great user interfaces.
Our brand is what we want everyone to think about us. When everyone - both us and
the people around us - have a consistent understanding of what Vaadin is and what we
stand for, it enables that image to spread and amplify. This book defines what we want
that image to be. It defines what the Vaadin brand is.
I hope that You are as excited and proud of living and breathing the Vaadin brand as
I am. You are the one who is shaping what everyone thinks about Vaadin - using this
brand as a tool and a guideline every day.
Let’s fight for simplicity for both the users and the developers!
Joonas Lehtinen
Founder & CEO
Vaadin
I N T R O D U C T I O N
W I T H C O R E J AVA 8 - 11 A N D B E Y O N D

2. S V E N R U P P E R T
Developer Advocate @ Vaadin
5
C O D I N G J AVA S I N C E 1 9 9 6
C O N S U LT I N G W O R L D W I D E
Public Sector: Military / Government
Private Sector: Automotive / Aerospace / SMB /
NonProfit / NonGov: World Bank / UN / YPARD / CGIAR
D I S T R I B U T E D S Y S T E M S S I N C E 2 0 0 2
J O I N E D VA A D I N 2 0 1 7

3. I N T R O
D I F F E R E N C E S B E T W E E N O O A N D F P I N J AVA

4. 4
@SvenRuppertJava8 - Optional<T>
the border between OO and FP in Java is not 100% clear.

5. @SvenRuppert
S I N C E J AVA 8
Functional Interfaces - basics

6. 6
@SvenRuppertJava8 - Functional Interfaces

7. 7
@SvenRuppertJava8 - Functional Interfaces

8. 8
@SvenRuppertJava8 - Functional Interfaces

9. 9
@SvenRuppertJava8 - Functional Interfaces

10. 10
@SvenRuppertJava9 - Functional Interfaces
Java9 - JEP213

11. @SvenRuppert
E X E R C I S E S
S I N C E J AVA 8
Functional Interfaces - basics

12. @SvenRuppert
S I N C E J AVA 8
Optional<T>

13. Optional<T> @SvenRuppert

14. Optional<T> @SvenRuppert

15. Optional<T> @SvenRuppert

16. Optional<T> - since JDK10 @SvenRuppert

17. @SvenRuppert
E X E R C I S E S
S I N C E J AVA 8
Optional<T>

18. @SvenRuppert
S I N C E J AVA 8
Result<T>

19. Optional<T> @SvenRuppert
Not symmetric
Not async - blocking only
Not functional enough
Declared final - no inheritance Having ValueTypes in mind
We need something

20. Result<T> @SvenRuppert
Must be easy to transform Optional <-> Result
Should work as an Drop-In-Replacement
Should connect to the Reactive-World
Should be symmetric
Must fit functional style / oo style

21. Result<T> @SvenRuppert
Transform from and to an Optional
pos. and neg. available

22. @SvenRuppert
Symmetric
Handle both ways
Result<T>

23. @SvenRuppert
Handle both ways
Async if needed
Result<T>

24. @SvenRuppert
Combine with Value and Transformation
Async if needed
Result<T>

25. @SvenRuppert
Combine with Value / Function
Async if needed
Combine with a function
Result<T>

26. @SvenRuppert
E X E R C I S E S
S I N C E J AVA 8
Result<T>

27. @SvenRuppert
S I N C E J AVA 8
Exceptions

28. Exceptions @SvenRuppert

29. Exceptions @SvenRuppert

30. Exceptions @SvenRuppert

31. Exceptions @SvenRuppert
JDK9

32. Exceptions @SvenRuppert

33. Exceptions @SvenRuppert

34. Exceptions @SvenRuppert

35. Exceptions @SvenRuppert

36. Exceptions @SvenRuppert

37. Exceptions @SvenRuppert

38. Exceptions @SvenRuppert
different exceptions

39. @SvenRuppert
E X E R C I S E S
S I N C E J AVA 8
Exceptions

40. @SvenRuppert
H O W T O U S E F U N C T I O N S …
Functions - Basics

41. Functions - Java8
41
@SvenRuppert
a function is a transformation
input -> output
(input - type, input value) (output - type, output value)

42. Functions - Java8
42
@SvenRuppert

43. 43
@SvenRuppertFunctions - Java8

44. 44
@SvenRuppertFunctions - Java8

45. 45
@SvenRuppertFunctions - Java8

46. 46
@SvenRuppert
Compose is not so nice.. but
Functions - Java8

47. 47
@SvenRuppert
Attention : make a semantic equal function !!
Functions - Java8

48. 48
@SvenRuppertFunctions - Java8
How to get an instance of a function?

49. 49
@SvenRuppertFunctions - Java8

50. 50
@SvenRuppertFunctions - Java8

51. 51
@SvenRuppertFunctions - Java8

52. Functions - Java8 - extract the logic !
52
@SvenRuppert

53. 53
@SvenRuppertFunctions - Java8

54. 54
@SvenRuppertFunctions - Java8

55. @SvenRuppert
E X E R C I S E S
H O W T O U S E F U N C T I O N S …
Functions - Basics

56. @SvenRuppert
G E N E R I C B A C K A N D F O R WA R D
Currying

57. Currying @SvenRuppert

58. @SvenRuppertCurrying

59. @SvenRuppertCurrying

60. @SvenRuppertCurrying

61. @SvenRuppert
E X E R C I S E S
G E N E R I C B A C K A N D F O R WA R D
Currying

62. @SvenRuppert
P U R E F U N C T I O N A L B E H AV I O R
Memoizing

63. Memoizing @SvenRuppert

64. Memoizing @SvenRuppert

65. Memoizing @SvenRuppert

66. Memoizing @SvenRuppert

67. Memoizing @SvenRuppert

68. Memoizing @SvenRuppert

69. Memoizing @SvenRuppert

70. Memoizing @SvenRuppert

71. Memoizing @SvenRuppert

72. Memoizing @SvenRuppert

73. Memoizing @SvenRuppert

74. @SvenRuppert
E X E R C I S E S
P U R E F U N C T I O N A L B E H AV I O R
Memoizing

75. @SvenRuppert
H O W T O D E C I D E ?
Case

76. Case @SvenRuppert

77. @SvenRuppertCase

78. @SvenRuppertCase

79. @SvenRuppertCase

80. @SvenRuppertCase

81. @SvenRuppert
E X E R C I S E S
H O W T O D E C I D E ?
Case

82. @SvenRuppert
H O W T O U S E , H O W T O B U I L D
Streams

83. Streams @SvenRuppert

84. Streams @SvenRuppert
A Stream is active after creation
want to define a Stream without starting it
maybe creating it interactively
we need a function !
Function<T, Stream<R>>

85. @SvenRuppert
E X E R C I S E S
H O W T O U S E , H O W T O B U I L D
Streams

86. Refactoring example
based on Java8
@SvenRuppert

87. 86
@SvenRuppertJava8 - Functional Interfaces - Example
typical legacy implementation

88. 87
@SvenRuppertJava8 - Functional Interfaces - Example
typical legacy implementation

89. 88
@SvenRuppertJava8 - Functional Interfaces - Example

90. 89
@SvenRuppertJava8 - Functional Interfaces - Example

91. 90
@SvenRuppertJava8 - Functional Interfaces - Example

92. 91
@SvenRuppertJava8 - Functional Interfaces - Example

93. 92
@SvenRuppertJava8 - Functional Interfaces - Example

94. 93
@SvenRuppertJava8 - Functional Interfaces - Example
Sourcecode is on github

95. Pattern in Java 8/9
how pattern will change…
@SvenRuppert

96. Virtual Proxy
94
@SvenRuppert

97. Virtual Proxy
95
@SvenRuppert
public class ServiceProxy implements Service {
private Service service = new ServiceImpl();
public String work(String txt) { return service.work(txt); }
}
What could we
change now ? Virtual Proxy:
create the Delegator later
public class VirtualService implements Service {
private Service service = null;
public String work(String txt) {
if(service == null) { service = new ServiceImpl(); }
return service.work(txt);
}
}

98. Virtual Proxy
96
@SvenRuppert
public class VirtualService implements Service {
private Service service = null;
public String work(String txt) {
if(service == null) { service = new ServiceImpl(); }
return service.work(txt);
}
}
This is NOT ThreadSafe
fixed decision for
an implementation
how to combine it with
a FactoryPattern ?

99. Virtual Proxy
97
@SvenRuppert
if(service == null) { service = new ServiceImpl(); }
public interface ServiceFactory {
Service createInstance();
}
public interface ServiceStrategyFactory {
Service realSubject(ServiceFactory factory);
}

100. Virtual Proxy - Not - ThreadSafe
98
@SvenRuppert
if(service == null) { service = new ServiceImpl(); }
public class ServiceStrategyFactoryImpl implements ServiceStrategyFactory {
Service realSubject;
public Service realSubject(final ServiceFactory factory) {
if (realSubject == null) {
realSubject = factory.createInstance();
}
return realSubject;
}
}
private ServiceFactory serviceFactory = ServiceImpl::new;

101. Virtual Proxy - Not - ThreadSafe
99
@SvenRuppert
if(service == null) { service = new ServiceImpl(); }
public class ServiceProxy implements Service {
private ServiceFactory serviceFactory = ServiceImpl::new;
private ServiceStrategyFactory strategyFactory = new ServiceStrategyFactoryImpl();
public String work(String txt) {
return strategyFactory .realSubject(serviceFactory).work(txt);
}
}

102. Virtual Proxy - Show some code….
100
@SvenRuppert

103. Virtual Proxy - Show some code….
101
@SvenRuppert

104. Virtual Proxy - Show some code….
102
@SvenRuppert

105. Virtual Proxy - Show some code….
103
@SvenRuppert

106. Virtual Proxy - Show some code….
104
@SvenRuppert

107. Virtual Proxy - Show some code….
105
@SvenRuppert

108. Virtual Proxy - Show some code….
106
@SvenRuppert

109. Virtual Proxy - Show some code….
107
@SvenRuppert

110. Virtual Proxy - Show some code….
108
@SvenRuppert

111. Virtual Proxy - Show some code….
109
@SvenRuppert

112. Decorator - pre Java8
110
@SvenRuppert

113. Decorator - pre Java8
111
@SvenRuppert

114. Decorator - pre Java8
112
@SvenRuppert

115. Decorator - pre Java8
113
@SvenRuppert

116. Decorator - Java8
114
@SvenRuppert

117. Decorator - Java8
115
@SvenRuppert

118. Decorator - Java8
116
@SvenRuppert

119. Decorator - Java8 - modify orig Interface
117
@SvenRuppert

120. Decorator - Java8 - DoubleUnaryOperator
118
@SvenRuppert

121. Interpreter - pre Java8
119
@SvenRuppert

122. Interpreter - pre Java8
120
@SvenRuppert

123. Interpreter - pre Java8
121
@SvenRuppert

124. Interpreter - pre Java8
122
@SvenRuppert

125. Interpreter - Java8 - Java9
123
@SvenRuppert

126. Interpreter - Java8 - Java9
124
@SvenRuppert
Main Idea - DataStructure to Function

127. Interpreter - Java8 - Java9
125
@SvenRuppert

128. @SvenRuppert
H O W R E A C T I V E W I L L S TA R T
Observer

129. 127
@SvenRuppertObserver

130. 128
@SvenRuppertObserver

131. 129
@SvenRuppertObserver

132. 130
@SvenRuppertObserver
key not needed anymore

133. 131
@SvenRuppertObserver

134. 132
@SvenRuppertObserver H O W T O C H A I N O B S E R V E R ?

135. @SvenRuppert
E X E R C I S E S
H O W R E A C T I V E W I L L S TA R T
Observer

136. @SvenRuppert
H O W T O U S E F U N C T I O N S … A S Y N C …
CompletableFuture

137. 135
@SvenRuppertJava8 - CompletableFuture
Process
Thread
Fiber
CompletionStage CompletionStage CompletionStage

138. 136
@SvenRuppertJava8 - CompletableFuture

139. 137
@SvenRuppertJava8 - CompletableFuture

140. 138
@SvenRuppert
Operator 1
Value A
Operator 2a
Result
Value B Value C
Java8 - CompletableFuture

141. 139
@SvenRuppertJava8 - CompletableFuture

142. 140
@SvenRuppertJava8 - CompletableFuture

143. 141
@SvenRuppertJava8 - CompletableFuture

144. 142
@SvenRuppertJava8 - CompletableFuture
Operator 1
Value A
Operator 2a
Result
Value B Value C

145. @SvenRuppert
E X E R C I S E S
H O W T O U S E F U N C T I O N S … A S Y N C …
CompletableFuture

146. @SvenRuppert
H O W T O C R E AT E A G R A P H E A S Y. .
CompletableFutureQueue

147. 145
@SvenRuppertCompletableFutureQueue
CompletableFuture is active after creation
want to define a CompletableFuture without starting it
maybe creating it interactively
we need a function !
Function<T, CompletableFuture<R>>

148. 146
@SvenRuppertCompletableFutureQueue

149. 147
@SvenRuppertCompletableFutureQueue

150. @SvenRuppert
E X E R C I S E S
H O W T O C R E AT E A G R A P H E A S Y. .
CompletableFutureQueue

151. Java 9
some nice news…
@SvenRuppert

152. Java9 - Optional
149
@SvenRuppert

153. Java9 - JEP266
150
@SvenRuppert
we got Publisher / Subscriber

154. @SvenRuppert
I N T E R FA C E O R I M P L E M E N TAT I O N ?
Var

155. @SvenRuppert
E X E R C I S E S
I N T E R FA C E O R I M P L E M E N TAT I O N ?
Var

156. Summary
X
@SvenRuppert
places to read more about it
www.functional-reactive.org
https://github.com/functional-reactive

157. Summary
153
@SvenRuppert
please, follow me ;-)
@SvenRuppert
Thank You !!!