This webinar by Oleksandr Navka (Lead Software Engineer, Consultant, GlobalLogic) was delivered at Java Community Webinar #1 on August 12, 2020. Webinar agenda: - The new structural unit of the program is Java Records - Updated instanceof statement - Updated switch operator More details and presentation: https://www.globallogic.com/ua/about/events/java-community-webinar-1/

1. 1
Java 14 Pattern Matching
Oleksandr Navka
Lead Software Engineer, Consultant, GlobalLogic

2. 2
1. Updated instanceof
2. Updated switch-case
3. Java Records
Agenda

3. 3
Тагир Валеев
JetBrains
Pattern matching
и его воображаемые друзья

4. 4

5. 5
When someone match something :)
What is pattern matching?

6. 6
Any pattern
• _
Constant pattern
• 1
• true
• null
Type pattern
• String s
Var pattern
• var i = 1
Deconstruction pattern
• Optional(String s)
• Node(Node left, Node right)
What are the patterns?

7. 7
Instanceof

8. 8
public class Animal {
}
class Dog extends Animal {
public void bark() {
}
}
class Cat extends Animal {
public void meow() {
}
}

9. 9
public static void say(Animal animal) {
if (animal instanceof Dog) {
Dog dog = (Dog) animal;
dog.bark();
} else if (animal instanceof Cat) {
Cat cat = (Cat) animal;
cat.meow();
}
}

10. 10
public static void say(Animal animal) {
if (animal instanceof Dog) {
Dog dog = (Dog) animal;
dog.bark();
} else if (animal instanceof Cat) {
Cat cat = (Cat) animal;
cat.meow();
}
}

11. 11
public static void say(Animal animal) {
if (animal instanceof Dog dog) {
dog.bark();
} else if (animal instanceof Cat cat) {
cat.meow();
}
}

12. 12
public static void say(Animal animal) {
if (animal instanceof Dog dog) {
dog.bark();
} else if (animal instanceof Cat cat) {
cat.meow();
}
}

13. 13
Before:
expression istanceof Type
Now:
expression instanceof Pattern

14. 14
Scoping

15. 15
if (obj instanceof String s) {
// can use s here
} else {
// can't use s here
}

16. 16
if (obj instanceof String s) {
// can use s here
} else {
// can't use s here
}
binding variable

17. 17
if (!(obj instanceof String s)) {
} else {
s.contains("a")
}

18. 18
if(obj instanceof String s && s.length() > 5) {
System.out.println(s.toUpperCase());
}

19. 19
if(obj instanceof String s || s.length() > 5) {
System.out.println(s.toUpperCase());
}

20. 20
if(!(obj instanceof String s) || s.length() > 5) {
System.out.println("Do something");
} else {
System.out.println(s.toUpperCase());
}

21. 21
if(!(obj instanceof String s) || s.length() > 5) {
System.out.println("Do something");
} else {
System.out.println(s.toUpperCase());
}

22. 22
if(!(obj instanceof String s) || s.length() > 5) {
throw new IllegalArgumentException();
}
System.out.println(s.toUpperCase());

23. 23
if(!(obj instanceof String s) || s.length() > 5) {
throw new IllegalArgumentException();
}
System.out.println(s.toUpperCase());

24. 24
if (!(obj instanceof String s)) {
s.contains(..)
} else {
s.contains(..)
}

25. 25
private String s = "abc";
if (!(obj instanceof String s)) {
s.contains(..)
} else {
s.contains(..)
}

26. 26
1. if (obj instanceof String s) {s.trim()}
2. if (!(obj instanceof String s)) {} else {s.contains("a")}
3. if(obj instanceof String s && s.length() > 5) {}
4. if(obj instanceof String s || s.length() > 5) {}
Binding variable scope

27. 27
1. if (obj instanceof String s) {s.trim()}
2. if (!(obj instanceof String s)) {} else {s.contains("a")}
3. if(obj instanceof String s && s.length() > 5) {}
4. if(obj instanceof String s || s.length() > 5) {}
Binding variable scope

28. 28
1. if (obj instanceof String s) {s.trim()}
2. if (!(obj instanceof String s)) {} else {s.contains("a")}
3. if(obj instanceof String s && s.length() > 5) {}
4. if(obj instanceof String s || s.length() > 5) {}
5. if(!(obj instanceof String s) || s.length() > 5) {}
6. if(!(obj instanceof String s) || s.length() > 5) {} else {s.toUpperCase());}
7. if(!(obj instanceof String s) || s.length() > 5) {
throw new IllegalArgumentException();
}
System.out.println(s.toUpperCase());
Binding variable scope

29. 29
1. instanceof has got type pattern matching
2. instanceof the first java feature that got pattern matching
3. Be aware about scoping
Instanceof Summary

30. 30
Switch - case

31. 31
public enum ProgrammingParadigm {OBJECT_ORIENTED, PROCEDURAL, FUNCTIONAL}
public static List<String> getProgrammingLanguage(ProgrammingParadigm programmingParadigm) {
List<String> languages = new ArrayList<>();
switch (programmingParadigm) {
case OBJECT_ORIENTED:
languages.add("Java");
languages.add("C++");
break;
case FUNCTIONAL:
languages.add("Haskel");
break;
case PROCEDURAL:
languages.add("Pascal");
break;
}
return languages;
}
Old version of switch

32. 32
public enum ProgrammingParadigm {OBJECT_ORIENTED, PROCEDURAL, FUNCTIONAL}
public static List<String> getProgrammingLanguage(ProgrammingParadigm programmingParadigm) {
List<String> languages = new ArrayList<>();
switch (programmingParadigm) {
case OBJECT_ORIENTED:
languages.add("Java");
languages.add("C++");
break;
case FUNCTIONAL:
languages.add("Haskel");
break;
case PROCEDURAL:
languages.add("Pascal");
break;
}
return languages;
}
Old version of switch

33. 33
public enum ProgrammingParadigm {OBJECT_ORIENTED, PROCEDURAL, FUNCTIONAL}
public static List<String> getProgrammingLanguage(ProgrammingParadigm programmingParadigm) {
List<String> languages = new ArrayList<>();
switch (programmingParadigm) {
case OBJECT_ORIENTED:
languages.add("Java");
languages.add("C++");
break;
case FUNCTIONAL:
languages.add("Haskel");
break;
case PROCEDURAL:
languages.add("Pascal");
break;
}
return languages;
}
Old version of switch
Input type limitations:
byte, short, char, and int
Enum Types, String

34. 34
public enum ProgrammingParadigm {OBJECT_ORIENTED, PROCEDURAL, FUNCTIONAL}
public static List<String> getProgrammingLanguage(ProgrammingParadigm programmingParadigm) {
List<String> languages = new ArrayList<>();
switch (programmingParadigm) {
case OBJECT_ORIENTED:
languages.add("Java");
languages.add("C++");
break;
case FUNCTIONAL:
languages.add("Haskel");
break;
case PROCEDURAL:
languages.add("Pascal");
break;
}
return languages;
}
Old version of switch
Can’t
get
result

35. 35
public static List<String> getProgrammingLanguage(ProgrammingParadigm programmingParadigm) {
switch (programmingParadigm) {
case OBJECT_ORIENTED:
return List.of("Java", "C++");
case FUNCTIONAL:
return List.of("Haskel");
case PROCEDURAL:
return List.of("Pascal");
default:
return List.of();
}
}

36. 36
public static List<String> getProgrammingLanguage(ProgrammingParadigm programmingParadigm) {
switch (programmingParadigm) {
case OBJECT_ORIENTED:
return List.of("Java", "C++");
case FUNCTIONAL:
return List.of("Haskel");
case PROCEDURAL:
return List.of("Pascal");
default:
return List.of();
}
}

37. 37
Disadvantages:
1. Always remember about break
2. Input data type limitation
3. Can’t get result
4. Don’t understand all possible options for enum
Old version of switch

38. 38
Pattern matching with switch case

39. 39
public void printObject(Object obj) {
switch (obj) {
case String s:
System.out.println("This is String" + s.trim());
break;
case Integer i:
System.out.println("This is Integer" + i);
break;
case Number n:
System.out.println("This is number"+ n);
break;
default:
System.out.println("I don't know");
}
}

40. 40
public void printObject(Object obj) {
switch (obj) {
case String s:
System.out.println("This is String" + s.trim());
break;
case Number n:
System.out.println("This is number"+ n);
break;
case Integer i:
System.out.println("This is Integer" + i);
break;
default:
System.out.println("I don't know");
}
}

41. 41
public void printObject(Object obj) {
switch (obj) {
case String s:
System.out.println("This is String" + s.trim());
break;
default:
System.out.println("I don't know");
case Number n:
System.out.println("This is number"+ n);
break;
case Integer i:
System.out.println("This is Integer" + i);
break;
}
}

42. 42
Updated switch case

43. 43
public static List<String> getProgrammingLanguage(ProgrammingParadigm programmingParadigm) {
return switch (programmingParadigm) {
case OBJECT_ORIENTED -> List.of("Java", "C++");
case FUNCTIONAL -> List.of("Haskel");
case PROCEDURAL -> List.of("Pascal");
};
}
Updated switch case

44. 44
public static List<String> getProgrammingLanguage(ProgrammingParadigm programmingParadigm) {
return switch (programmingParadigm) {
case OBJECT_ORIENTED -> {
System.out.println("You are master of polymorphism");
yield List.of("Java", "C++");
}
case FUNCTIONAL -> {
System.out.println("You are master of recursion");
yield List.of("Haskel");
}
case PROCEDURAL -> {
System.out.println("Try to use another paradigms");
yield List.of("Pascal");
}
};
}

45. 45
1. Don’t need to use break
2. Can return result
3. Don’t need to use default branch if all options described
4. Input data types have limitations
Summary of updated switch

46. 46
Java Records

47. 47
private record Car(int speed, String manufacturer) {
}
Java Records

48. 48
private record Car(int speed, String manufacturer) {
}
public static void main(String[] args) {
Car car = new Car(100, "Mercedes");
System.out.println(car.speed());
System.out.println(car.manufacturer());
}
Java Records

49. 49
private record Car(int speed, String manufacturer) {
}
public static void main(String[] args) {
Car car = new Car(100, "Mercedes");
System.out.println(car);
}
-------
Output:
Car[speed=100, manufacturer=Mercedes]
Java Records

50. 50
private static final class Car extends java.lang.Record {
private final int speed;
private final java.lang.String manufacturer;
public Car(int speed, java.lang.String manufacturer) { /* compiled code */ }
public java.lang.String toString() { /* compiled code */ }
public final int hashCode() { /* compiled code */ }
public final boolean equals(java.lang.Object o) { /* compiled code */ }
public int speed() { /* compiled code */ }
public java.lang.String manufacturer() { /* compiled code */ }
}

51. 51
private static final class Car extends java.lang.Record {
private final int speed;
private final java.lang.String manufacturer;
public Car(int speed, java.lang.String manufacturer) { /* compiled code */ }
public java.lang.String toString() { /* compiled code */ }
public final int hashCode() { /* compiled code */ }
public final boolean equals(java.lang.Object o) { /* compiled code */ }
public int speed() { /* compiled code */ }
public java.lang.String manufacturer() { /* compiled code */ }
}

52. 52
public abstract class Record {
protected Record() {}
@Override
public abstract boolean equals(Object obj);
@Override
public abstract int hashCode();
@Override
public abstract String toString();
}

53. 53
private static final class Car extends java.lang.Record {
private final int speed;
private final java.lang.String manufacturer;
public Car(int speed, java.lang.String manufacturer) { /* compiled code */ }
public java.lang.String toString() { /* compiled code */ }
public final int hashCode() { /* compiled code */ }
public final boolean equals(java.lang.Object o) { /* compiled code */ }
public int speed() { /* compiled code */ }
public java.lang.String manufacturer() { /* compiled code */ }
}

54. 54
private static final class Car extends java.lang.Record {
private final int speed;
private final java.lang.String manufacturer;
public Car(int speed, java.lang.String manufacturer) { /* compiled code */ }
public java.lang.String toString() { /* compiled code */ }
public final int hashCode() { /* compiled code */ }
public final boolean equals(java.lang.Object o) { /* compiled code */ }
public int speed() { /* compiled code */ }
public java.lang.String manufacturer() { /* compiled code */ }
}

55. 55
private record Car(int speed, String manufacturer) {
public Car {
if(speed < 0) {
throw new IllegalArgumentException();
}
}
}
public static void main(String[] args) {
var car = new Car(-2, "Mercedes");
System.out.println(car);
}
Canonical constructor

56. 56
private record Car(int speed, String manufacturer) {
public Car {
if(speed < 0) {
throw new IllegalArgumentException();
}
}
public Car(String manufacturer) {
this(0, manufacturer);
}
}
Canonical constructor

57. 57
private static final class Car extends java.lang.Record {
private final int speed;
private final java.lang.String manufacturer;
public Car(int speed, java.lang.String manufacturer) { /* compiled code */ }
public java.lang.String toString() { /* compiled code */ }
public final int hashCode() { /* compiled code */ }
public final boolean equals(java.lang.Object o) { /* compiled code */ }
public int speed() { /* compiled code */ }
public java.lang.String manufacturer() { /* compiled code */ }
}

58. 58
private static final class Car extends java.lang.Record {
private final int speed;
private final java.lang.String manufacturer;
public Car(int speed, java.lang.String manufacturer) { /* compiled code */ }
public java.lang.String toString() { /* compiled code */ }
public final int hashCode() { /* compiled code */ }
public final boolean equals(java.lang.Object o) { /* compiled code */ }
public int speed() { /* compiled code */ }
public java.lang.String manufacturer() { /* compiled code */ }
}

59. 59
1. Java 14 present first version of pattern matching
2. Type pattern matching present in instanceof operator
3. New Switch statement was released with some blanks for
pattern matching
4. Keep eye on Java Records and deconstruction patterns
Summary

60. 60
Thank You