The document provides an overview of the Java Collections Framework. It discusses key interfaces like List, Set, and Map and some of their common implementations like ArrayList, LinkedList, HashSet, and HashMap. It covers common operations on collections like add, remove, contains and how different implementations may have different performance and memory usage characteristics for those operations. The document also discusses topics like generics, null values, immutable collections and best practices when using the Collections Framework.

1. Collections
Framework
JJUG CCC 2019 spring C1
2019-05-18

2. #ccc_c1

3. •
• twitter: @mike_neck
• github : mike-neck
• L is B direct
(Java/Golang)

4. • Java
( )
• Java

5. •
• Queue
• Dequeue
• Optional …
•
•
•

6. • Collections Framework
• API
•
•

7. Collections
Framework

8. Java
• Java
Java
java.lang.String
int
com.app.Course

9. •
Java
java.uti.Set<com.app. >

10. •
Coffee[] coffees = new Coffee[];

11. (1)
•
•
•
(Effective Java 3rd ed No.59)
•

12. String[] array = …
String[] current = array;
String[] array = new String[current.length + 1];
System.arraycopy(current, 0, array, 0, current.length);
array[current.length] = "foo";

13. List<E>
List<String> list = …
list.add("foo");

14. (2)
•
• Java
•

15. Coffee
CaffeMocha
Coffee[]
CaffeMocha[]
Java CaffeMocha Coffee
CaffeMocha Coffee

16. Coffee
CaffeMocha
Coffee[]
CaffeMocha[]
Java CaffeMocha
Coffee

17. Coffee
CaffeMocha
Coffee[]
CaffeMocha[]
CaffeMocha[] CaffeMocha
CaffeMocha
( Coffee )

18. CaffeMocha[] caffeMochaArray = new CaffeMocha[1];
Coffee[] coffeeArray = caffeMochaArray;
coffeeArray[0] = new American(); // ArrayStoreException
Coffee Coffee
American

19. List<E>
(Java 5 )
Coffee
CaffeMocha
List<Coffee>
List<CaffeMocha>
List<Coffee> List<CaffeMocha>

20. List<CaffeMocha> caffeMochaList = new ArrayList<>();
List<Coffee> coffeeList = caffeMochaList; // compile error
List<Coffee> List<CaffeMocha>
List<Coffee>
List<CaffeMocha>

21. Collections Framework
•
• Java
• Collections Framework
• Collections Framework

22. API

23. • API
•

24. Iterable<T>
Collection<E>
List<E> Set<E> Map<K,V>
SortedSet<E> SortedMap<K,V>

25. Set<E>
• ( )
• ( )

26. SortedSet<E>
•
• ( )

27. List<E>
• (
)
•
0 1 2 3 4 5

28. Map<K,V>
• K (Set) V
• ( -> )
350JPY
550JPY
450JPY
350JPY

29. Collection<E>
• ( )
• / / / /

30. •
•
• ( )
•
•
•
UnsupportedOperationException
( )

31. !

32. Iterable<T>
Iterable<T>
Collection<E>
List<E> Set<E> Map<K,V>

33. Iterable<E>
• Iterator<E> iterator()
• Iterator<E> ( )
Iterable<String> iterable = ...;
Iterator<String> iterator = iterable.iterator();
while(iterator.hasNext()) {
String string = iterator.next();
System.out.println(string);
}

34. Iterable<E> (1)
• Iterable<E> for
Iterable<String> iterable = ...;
for(String item : iterable) {

35. • forEach(Consumer<? extends E>)
Iterable<E> (2)
Iterable<String> iterable = ...;
iterable.forEach(string -> System.out.println(string));

36. Collection<E>
Iterable<E>
Collection<E>
List<E> Set<E> Map<K,V>

37. Collection<E>
•
• boolean isEmpty()
• int size()
•
• boolean contains(Object)
• boolean
containsAll(Collection<?>)
• /
• E[] toArray(E[])
• Stream<E> stream()
•
• boolean add(E)
• boolean addAll(Collection<E>)
•
• boolean remove(E)
• true
• boolean removeAll(Collection<?>)
• boolean retainAll(Collection<?>)
• boolean removeIf(Predicate<? super E>)
• 1 true
•
• void clear()
!
!

38. Collection<E>
• ID

39. Collection<E>
public Collection<CoffeeSale> findCoffeeSales(
Instant date, Collection<CoffeeId> coffeeIds) {
// cofeeIds 0 return
if (coffeeIds.isEmpty()) {
return Collections.emptyList();
}
//
}

40. removeAll(Collection)
collection.removeAll(parameter);
collection parametercollection

41. retainAll(Collection)
collection.retainAll(parameter);
parametercollection

42. Set<E>
Iterable<E>
Collection<E>
List<E> Set<E> Map<K,V>
SortedSet<E> SortedMap<K,V>

43. Collection<E>
Collection<E>
( ) Set<E>

44. List<E>
Iterable<E>
Collection<E>
List<E> Set<E> Map<K,V>

45. List<E>
•
• E get(int)
•
• int indexOf(Object)
• int lastIndexOf(Object)
• List
• List<E> subList(int, int)
• ( )
• void add(int, E)
• void addAll(int,
Collection<E>)
•
• void set(int, E)
• void
replaceAll(UnrayOperator<E>
)
•
• void sort(Comparator<E>)
•
• E remove(int)
!
!

46. List#remove(int)
List<Integer> list = new ArrayList<>(
List.of(1, 2, 3, 4, 5));
// remove(int)? remove(E)?
list.remove(1);
!

47. Map<K,V>
Iterable<E>
Collection<E>
List<E> Set<E> Map<K,V>

48. Map<K,V>
•
• V get(K)
• V getOrDefault(K,V)
•
• boolean
containsKey(Object)
• boolean
containsValue(Object)
•
• int size()
• boolean isEmpty()
• /
• Set<K> keySet()
• Collection<V> values()
• Set<Map.Entry<K,V>>
entrySet()
• void forEach(BiConsumer<?
super K, ? super T>)

49. Map<K,V>
get
•
Map<CoffeeName, CoffeeProduct> coffees;
CoffeeProduct findProduct(CoffeeName name) {
return coffees.get(name);
}
CoffeeProduct product = coffeeRepository
.findProduct(coffeeName(" "));
Order newOrder = product.createNewOrder(1); // NullPointerException

50. Map<K,V>
get
• Optional<T>
Map<CoffeeName, CoffeeProduct> coffees;
Optional<CoffeeProduct> findProduct(CoffeeName name) {
return Optional.ofNullable(coffees.get(name));
}
Optional<CoffeeProduct> product = coffeeRepository
.findProduct(coffeeName(" "));
Optional<Order> newOrder = product.map(p -> p.createNewOrder(1));

51. Map<K,V>
• Java8
• V put(K, V)
• void putAll(Map<? extends
K, ? extends V>)
• Java 8
• V putIfAbsent(K, V)
• V compute(K, BiFunction<?
super K, ? super V, ? extends
V>)
• V computeIfAbsent(K,
Function<? super K, ? extends
V>)
!
• Java 8
• V replace(K, V)
• boolean replace(K, V, V)
• void replaceAll(BiFunction<?
super K, ? super V, ?
extends V>)
• V computeIfPresent(K,
Function<? super K, ?
extends V>)
• V merge(K, V, BiFunction<?
super V, ? super V, ?
extends V>)

53. put(K,V)
put(K,V)
putIfAbsent(K,V) replace(K,V)
put(K,V)
putIfAbsent/replace

54. compute
•
• Stream
(10 ) DrinkProduct
DrinkName
DrinkCategory
Price

55. Map<DrinkCategory,List<DrinkProduct>> groupByCategory(
List<DrinkProduct> list) {
Map<DrinkCategory,List<DrinkProduct>> map = new HashMap<>();
for(DrinkProduct product: list) {
if(!map.containsKey(product.category)) {
map.put(product.category, new ArrayList<>());
}
map.get(product.category).add(product);
}
return Collections.unmodifiableMap(map);
}

56. Map<DrinkCategory,List<DrinkProduct>> groupByCategory(
List<DrinkProduct> list) {
Map<DrinkCategory,List<DrinkProduct>> map = new HashMap<>();
for(DrinkProduct product: list) {
map.computeIfAbsent(product.category, k -> new ArrayList<>())
.add(product);
}
return Collections.unmodifiableMap(map);
}

57. Map<K,V>
•
• V remove(Object)
• boolean remove(Object, Object)
•
• void clear()
!

58. •
• (Set/List/Map)
•
UnsupportedOperationException

60. List<E>
• … add/remove/sort
• ArrayList<E> -
List<E>
• LinkedList<E> -
List<E>

61. ArrayList<E> vs
LinkedList<E>
• pros
• ArrayList<E> -
• LinkedList<E> - /
• cons
• ArrayList<E> -
• LinkedList<E> -

62. LinkedList Queue
Dequeue(Stack)
ArrayList LinkedList
ArrayList

63. List<E>
• … add/remove/sort
UnsupportedOperationException
•
• List.of(E…)
• List.copyOf(Collection<? extends E>)
• Arrays.asList(E…)
• Collections.emptyList()
• Collections.singletonList(E)
• Collections.unmodifiableList(List<? extends E>)

64. Set<E>/SortedSet<E>
• … add/remove
• HashSet<E> - hashCode
Set<E>
• HashMap<E, Object>
• LinkedHashSet<E> - HashSet<E> ( )
Set<E>
• LinkedHashMap<E, Object>
• TreeSet<E> - SortedSet<E> /Comparator<E>
• TreeMap<E, Object>

65. Set<Coffee>
Set<E> Map<K,V>
Set<Price>
350 JPY
450 JPY
550 JPY

66. Set<Coffee>
Set<E> Map<K,V>
Set<Price>
350 JPY
450 JPY
550 JPY

67. Collection<Price>
IdentifiedBy<Coffee>
Set<E> Map<K,V>
350 JPY
350 JPY
450 JPY
550 JPY

68. Map<Coffee,Price>
Set<E> Map<K,V>
350 JPY
350 JPY
450 JPY
550 JPY

69. Set<E>
• … add/remove/sort
UnsupportedOperationException
•
• Set.of(E…)
• Set.copyOf(Collection<? extends E>)
• Collections.emptySet()
• Collections.singleton(E)
• Collections.unmodifiableSet(List<? extends E>)

70. Map<K,V>
• … put/remove
• HashMap<K,V> - hashCode
Map<K,V>
• LinkedHashMap<K,V> - HashMap<K,V>
( )
Map<K,V>
• TreeMap<K,V> - SortedMap<K,V>

71. HashMap<K,V>
Map<ProductId, DrinkProduct> toMap(SortedSet<DrinkProduct> set) {
Map<ProductId, DrinkProduct> map = new HashMap<>();
for(DrinkProduct product: set) {
map.put(product.id, product);
}
return Collections.unmodifiableMap(map);
}
Map<ProductId, DrinkProduct> map = toMap(products);
map.forEach((id, product) -> System.out.println(id));

72. HashMap<K,V>
Map<ProductId, DrinkProduct> toMap(SortedSet<DrinkProduct> set) {
Map<ProductId, DrinkProduct> map = new LinkedHashMap<>();
for(DrinkProduct product: set) {
map.put(product.id, product);
}
return Collections.unmodifiableMap(map);
}
Map<ProductId, DrinkProduct> map = toMap(products);
map.forEach((id, product) -> System.out.println(id));
LinkedHashMap<K,V>

73. Map<K,V>
• … put/remove/compute
UnsupportedOperationException
•
• Map.of(K,V)
• Map.copyOf(Map<? extends K,? extends V>)
• Collections.emptyMap()
• Collections.singletonMap(K,V)
• Collections.unmodifiableMap(Map<? extends K,?
extends V>)

74. •
•

75. 6

76. 6
•
• equals/hashCode
• ( )
• (
)
• null
• null
• Map<String, ?>

77. I. equals/hashCode
• equals
contains(containsKey)
• Set<E> add
• HashSet hashCode
hashCode

78. equals
• : x.equals(x) true (x ≠ null)
• : x.equals(y) true y.equals(x) true
(x ≠ null, y ≠ null)
• : x.equals(y) true y.equals(z) true
z.equals(x) true (x ≠ null, y ≠ null, z ≠ null)
• : x.equals(y)
• x.equals(null) false (x ≠ null)
• equals NullPointerException

79. hashCode
• equals hashCode
• x.equals(y) true x.hashCode()
y.hashCode()
• hashCode()
• x.equals(y) false x y hashCode()

80. equals/hashCode
•
• IDE
•
• Lombok
•
• google/auto AutoValue
• IDE

81. II.
• Java 1.4 Java 5
•
List<String> List

82. void unsafeAdd(List list, Object o) {
list.add(o);
}
List<String> list = new ArrayList<>(List.of("foo"));
unsafeAdd(list, 100L);
for(String string : list) { // ClassCastException
String.out.println(string);
}
!

83. <E, F extends E> void unsafeAdd(List<? super E> list, F o) {
list.add(o);
}
List<String> list = new ArrayList<>(List.of("foo"));
unsafeAdd(list, 100L); // compile error

84. III.
• List<E>
(ArrayList<E>/LinkedList<E>)
(List.of()/Arrays.asList())
• Collections Framework
(add/remove/clear)

85. void addSomeEntry(List<String> list) {
list.add("bar"); // UnsupportedOperationException
}
List<String> list = List.of("foo");
unsafeAdd(list);
!

86. •
UnsupportedOperationException
•
• ( )
• ArrayList<E>/
LinkedList<E>
•

87. List<String> someEntry() {
return List.of("bar"); //
}
List<String> list = new ArrayList<>(List.of(“foo"));
list.addAll(someEntry());

88. IV. null
• null
• ArrayList<E>/LinkedList<E>/Arrays.asList()/
HashSet<E>/HashMap<K,V>
• null
• List.of()/Set.of()/Map.of() /
TreeSet<E>/TreeMap<E>
• API

89. null
List<String> someEntry() {
List<String> list = new ArrayList<>();
list.add(null);
list.add("foo");
return list;
}
List<String> list = new ArrayList<>(List.of(“bar"));
list.addAll(someEntry());
return List.copyOf(list)); // NullPointerException
!

90. null
: null add
( )
List<String> someEntry() {
List<String> list = new ArrayList<>();
list.add("foo");
return list;
}
List<String> list = new ArrayList<>(List.of("bar"));
list.addAll(someEntry());
return List.copyOf(list));

91. null
: ArrayList
findbugs/spotbugs
class ListBuilder<E>{
final List<E> list = new ListBuilder<>();
final add(@Nonnull E e) {
list.add(e);
}
}
List<String> someEntry() {
ListBuilder<String> listBuilder = new ListBuilder<>();
listBuilder.add("foo");
return listBuilder.getList();
}

92. V.
null
• IV
•

93. null
List<String> someEntries(Key key) {
return map.get(key);
}
List<String> list = someEntries();
return list.size(); // NullPointerException
!

94. null
List<String> someEntries(Key key) {
return map.getOrDefault(key, Collections.emptyList());
}
List<String> list = someEntries();
return list.size(); // 0

95. VI.
Map<String,Object>
• Map<String,Object>
• Map<String,Object>
•

96. Map<String,Object>
PUT /users/1234
{“type":"image",
"file":"https://example.com/files/123"}
PUT /users/1234
{"type":"fields",
"name":" ",
"color":"#009933"}

97. Map<String,Object>
void updateProfile(UserId userId, Map<String,Object> newProfile) {
if(newProfile.get("type") != null &&
newProfile.get("type").equals("image")) {
String file = (String) newProfile.get("file");
if(file == null) {
throw new IllegalArgumentException("invalid parameter");
}
updateProfileImage(userId, newProfile);
} else if(newProfile.get("type") != null &&
newProfile.get(“type").equals("fields")) {
String name = (String) newProfile.get("name");
String color = (String) newProfile.get("color");
String url = (String) newProfile.get("url");
updateNameAndColor(userId, name, color, url);
!

98. Map<String,Object>
void updateProfileImage(UserId userId, NewProfileImage newProfileImage) {
if(newProfileImage.notHavingImageUrl()) {
throw new IllegalArgumentException("invalid parameter");
}
Optional<ProfileImageUrl> currentUrl = imageRepository.findProfileImageUrl(userId);
if(currentUrl.filter(url -> url.sameUrl(newProfileImage)).isPresent()) {
imageRepository.update(newProfileImage);
}
}
void updateProfileImage(UserId userId, NewProfileFields newProfileFields) {
if(newProfileFields.satisfiesCondition(satisfiesCondition())) {
throw new IllegalArgumentException("invalid parameter");
}
profileRepository.update(newProfileFields);
}

99. …

100. •
Acroquest Technology Java (
2017 )
• Joshua Bloch Effective Java 3
( 2018 )
• (Web) Dan Becker, HOW-TO Get started with the
Java Collections Framework(JAVA WORLD FROM IDG,
1998, https://www.javaworld.com/article/2076800/
get-started-with-the-java-collections-
framework.html)

103. 1. ArrayList

104. ArrayList<E>
(Object[])

105. add(int, E)
ArrayList<E>

106. ArrayList<E>

107. ArrayList<E>

108. 2. LinkedList

109. LinkedList<E>
previous
next
previous
next
previous
next
first last
Node<E>
LinkedList Node<E>

110. LinkedList<E>
previous
next
previous
next
previous
next
add(int, E)

111. LinkedList<E>
previous
next
previous
next
previous
next
Node<E>
previous
next

112. LinkedList<E>
previous
next
previous
next
previous
next
(next/previous)
previous
next

113. 3. ArrayList vs
LinkedList

114. ArrayList vs LinkedList
add(E) - throughput/ms
ArrayList
LinkedList
JDK: oracle openjdk 12.0.1 / OS: Amazon Linux2 /
: m5a.large / : Xmx256M,Xms256M

115. ArrayList vs LinkedList
add(0,E) - throughput/ms
ArrayList
LinkedList
JDK: oracle openjdk 12.0.1 / OS: Amazon Linux2 /
: m5a.large / : Xmx256M,Xms256M

116. ArrayList vs LinkedList
get(int) - throughput/ms
ArrayList
LinkedList
JDK: oracle openjdk 12.0.1 / OS: Amazon Linux2 /
: m5a.large / : Xmx256M,Xms256M

117. ArrayList vs LinkedList
forEach(Consumer) - throughput/ms
ArrayList
LinkedList
JDK: oracle openjdk 12.0.1 / OS: Amazon Linux2 /
: m5a.large / : Xmx256M,Xms256M

118. 4. HashMap

119. HashMap<E>
Node
K key
int hash/K key/V value Node
int hash
V value
next

120. HashMap<E>
Node (Node[])
length

121. HashMap<E>
Node index Node hash
mod
Node
hash
length
index

122. HashMap<E>
index LinkedList
next next

123. HashMap<E>
index LinkedList
next next
LinkedList

124. HashMap<E>
LinkedList
hashCode
B
R
left
right
R

125. 5. TreeMap

126. TreeMap<K,V>
• TreeMap<K,V>
•
•
• K key V value
•
•
• ( )

127. TreeMap<K,V>
•
• ( )
•
•
•
•

128. TreeMap<K,V>
74
3
key:
value:
4
key:4 key:7
4 7

129. TreeMap<K,V>
7
3
key:
value:
4
key:3 key:7
key:3 key:4
3

130. TreeMap<K,V>
7
key:
value:
4
3

131. TreeMap<K,V>
7
4
3
← (4)
4
73