Рассмотрим актуальность в свете обновлений Java 8/9, покажем, как можно начать использовать Scala в Java проектах.

1. Scala for the doubters
Max Klyga

2. –James Gosling
“If

3. I

4. were

5. to

6. pick

7. a

8. language

9. to

10.
use

11. today

12. other

13. than

14. Java,

15. it

16.
would

17. be

18. Scala.”

20. Scala

21. –James Iry, “A Brief, Incomplete, and Mostly Wrong History of Programming
Languages”
“A

22. drunken

23. Martin

24. Odersky

25. sees

26. a

27. Reese's

28.
Peanut

29. Butter

30. Cup

31. ad

32. featuring

33. somebody's

34.
peanut

35. butter

36. getting

37. on

38. somebody

39. else's

40.
chocolate

41. and

42. has

43. an

44. idea.

45. He

46. creates

47. Scala,

48. a

49.
language

50. that

51. unifies

52. constructs

53. from

54. both

55.
object

56. oriented

57. and

58. functional

59. languages.

60. This

61.
pisses

62. off

63. both

64. groups

65. and

66. each

67. promptly

68.
declares

69. jihad.”

71. Scala
OOP FP

73. Lightweight syntax
object Main extends Application {
val phonebook = Map(
Alice - 212-34-56,
Bob - 265-43-21
)
phonebook += (Carl - 298-76-54)
println(phonebook(Alice))
for (i - 1 to 10) {
println(i)
}
}
Scala

74. Lightweight syntax
public class Person
{
private String firstName;
private String lastName;
String getFirstName() { return firstName; }
void setFirstName(String firstName) { this.firstName = firstName; }
String getLastName() { return lastName; }
void setLastName(String lastName) { this.lastName = lastName; }
int hashCode() { .... }
boolean equals(Object o) { .... }
}
Java

75. Lightweight syntax
case class Person(var firstName:String, var lastName:String)
Scala

76. Lightweight syntax
boolean hasUpperCase = false;
for (int i = 0; i name.length(); ++i) {
if (Character.isUpperCase(name.charAt(i))) {
hasUpperCase = true;
break;
}
}
Java

77. Lightweight syntax
val hasUpperCase = name.exists(_.isUpperCase)
Scala

78. Lightweight syntax
PredicateCharacter isUpperCase = new PredicateCharacter() {
public Character apply(Character ch) {
return Character.isUpperCase(ch);
}
};
boolean hasUpperCase = Iterables.any(Lists.charactersOf(name), isUpperCase);
Java + Guava

79. Lightweight syntax
PredicateCharacter isUpperCase = (ch) - Character.isUpperCase(ch);
boolean hasUpperCase = Iterables.any(Lists.charactersOf(name), isUpperCase);
Java 8 + Guava

80. Lightweight syntax
boolean hasUpperCase = name.chars().anyMatch((ch) - Character.isUpperCase(ch));
Java 8

81. Lightweight syntax
boolean hasUpperCase = name.chars().anyMatch((ch) - Character.isUpperCase(ch));
Java 8
Scala
val hasUpperCase = name.exists(_.isUpperCase)

82. Lambdas
Java 8
•Can only access final variables
•Cannot mutate variables in outer scope
Scala
•Can access any variables
•Can mutate any accessible variables

83. Traits
Java 8
•Can define default methods in interfaces
(Java 9 allows private methods)
•“Diamond” inheritance is forbidden
Scala
•No restrictions on method implementation
•Method invocation chain determined by inheritance order

84. Composable
Everything is an expression

85. Composable
var x:Int
if (…) {
x = 10
} else {
x = 0
}

86. Composable
val x = if (…) {
10
} else {
0
}

87. Composable
var x = List[Int]()
for (i - 1 to 10) {
x = i :: x
}

88. Composable
var x = for (i - 1 to 10) {
yield i
}

89. Composable
Everything is an expression
if for while try match

90. Composable
Things nest

91. Composable
import com.dull.lib
class Eggs {
import org.cool.lib
def bacon {
import org.other.cool.lib
…
}
}

92. Composable
class Eggs {
def bacon {
def inner(…) {
def innerer {
…
}
…
}
…
}
}

93. Pattern matching
abstract class ChatProtocol
case class Message(userId:Int, text:String)
case class Join(userId:Int, name:String)
case class Leave(userId:Int)
command match {
case Message(id, text) = println(s${users(id)}: ${text})
case Join(id, name) = {
users += (id, name)
println(s${name} joined)
}
case Leave(id) = {
println(s${users(id)} left)
users -= id
}
}

94. REPL
Java 9 will finally get it too

96. –Alan Perlis
“Syntactic

97. sugar

98. causes

99.
cancer

100. of

101. the

102. semi-colons.”

107. Implicits
• Conversions
• Extension methods via Rich Interface Pattern
• Remove boilerplate code

108. Implicits
• Conversions
• Extension methods via Rich Interface Pattern
• Remove boilerplate code

109. Generic code
• Partial application
• Variance annotations
• Implicits
• Macros

110. With great power comes
great responsibility

111. Sleep of reason
produces monsters

112. Operator overloading
abuse
val intermediateHandler = (:/(host, port) / target ? params : identity)
https://github.com/dispatch/reboot
def root = jsonObj | jsonArray
def jsonObj = { ~ repsep(objEntry, ,) ~ } ^^ { case vals:List[_] = JSONObject(Map(vals:_*)) }
def jsonArray = [ ~ repsep(value, ,) ~ ] ^^ { case vals:List[_] = JSONArray(vals) }
def objEntry = stringVal ~ (: ~ value) ^^ { case x ~ y = (x, y) }
https://github.com/scala/scala-parser-combinators
Unicode operators in ScalaZ: ≠ ∋ ⇏ ★ ∅

113. Learning Scala will make you a
better Java programmer

114. –Paul Graham
“you

115. could

116. get

117. smarter

118. programmers

119. to

120. work

121.
on

122. a

123. Python

124. project

125. than

126. you

127. could

128. to

129. work

130.
on

131. a

132. Java

133. project.”

135. The Python
Paradox

136. The Scala Paradox

138. Java ❤ Scala

139. Java ❤ Scala
• Scala Maven plugin - http://davidb.github.io/scala-
maven-plugin/

140. Questions
Max Klyga
@Neku42