This document is a beginner's guide to Java Collections Framework. It introduces common data structures like lists, sets, queues and maps. It explains basic concepts like algorithms, collection types and implementations. It also covers operations on collections like iteration, sorting and filtering. The guide demonstrates how to select the appropriate data structure based on usage and provides examples of bulk operations using streams.

1. Collections Framework
Beginners guide II
HASUNUMA Kenji
k.hasunuma@coppermine.jp

2. Introduction

3. What's Collections?
• Major data structures
• Basic algorithm
• Simple and flexible design
• e.g. Concurrency, Hazelcast
• packaged in java.util.*

4. Algorithm and Data structures

5. Basic concepts
Algorithm Data structures

6. Basic concepts
Algorithm Data structures
Collections Collection
Map

7. Data structures
Collection<E> Map<K, V>
Set<E> List<E> Queue<E>
Deque<E>
Elements are
• Unordered
• No duplicate
• Sequential Access
key and value pairs
(Hash variable)
Elements are
• Ordered
• May duplicate
• Random Access Elements are
• Ordered
• May duplicate
• Sequential Access
Collection of values

8. Set<E> List<E> Deque<E> Map<K, V>
Hash
Table
HashSet -- -- HashMap
Resizable
Array
-- ArrayList ArrayDeque --
Balanced
Tree
TreeSet -- -- TreeMap
Linked
List
-- LinkedList LinkedList --
Hash Table
+
Linked List
Linked
HashSet
-- --
Linked
HashMap

9. Hash Table
Sequantial Access Slow
Random Access Fastest
Insert/Delete Fastest
Resizable
Array
Sequantial Access Fast (size dependent)
Random Access Fast (size dependent)
Insert/Delete Slow
Balanced
Tree
Sequantial Access Medium
Random Access Medium
Insert/Delete Fast (constant)
Linked List
Sequantial Access Fast (size dependent)
Random Access Slow
Insert/Delete Fast (size dependent)

10. How to select the type

11. How to select the type
1. Basic type
e.g. String, Integer, BigDecimal
2. Type of data structure
e.g. Set<E>, List<E>, Deque<E>, Map<K, V>
3. Implement of data structure
e.g. HashSet, TreeSet, ArrayList, LinkedList,
ArrayDeque, HashMap, TreeMap

12. #1: String, unordered, no duplicated
1. Basic type : String
2. Data structure : Set<String>
3. Implement : HashSet<String>
Set<String> set = new HashSet<>();

13. #2: int, ordered, random access
1. Basic type : Integer (as int)
2. Data structure : List<Integer>
3. Implement : ArrayList<Integer>
List<Integer> list = new ArrayList<>();

14. #3: String, ordered, random access,
insert or remove frequently
1. Basic type : String
2. Data structure : List<Integer>
3. Implement : LinkedList<Integer>
List<String> list = new LinkedList<>();

15. Basic operations

16. Methods of Collection<E>
• boolean add(E e)
• boolean remove(Object o)
• boolean isEmpty()
• int size()
• void clear()
• <T> T toArray(T[] a)

17. Methods of List<E>
• boolean add(int index, E element)
• E get(int index)
• E set(int index, E element)
• int remove(int index)
• int indexOf(Object o)
• int lastIndexOf(Object o)
For Random
Access

18. Methods of Deque<E>
• boolean offer(E element)
• boolean add(E element) w/Exception
• E poll()
• E remove() w/Exception
• E peek()
• E element() w/Exception
As Queue

19. Methods of Deque<E>
• void push(E element)
• E pop()
• E peek() As Stack

20. Methods of Map<K, V>
• V get(Object key)
• V getOrDefault(Object key, V value)
• V put(K key, V value)
• V putIfAbsent(K key, V value)
• V replace(K key, V value)
• V remove(Object key)

21. Methods of Map<K, V>
• Set<K> keySet()
• Collection<V> values()
• boolean containsKey(Object key)
• boolean containsValue(Object value)
• int size()
• void clear()

22. Algorithm : Collections
Provides general algorithms:
• Sort and shuffle elements (List)
• Reverse, fill and copy elements (List)
• Binary search (List)
• Minimum, maximum and frequency
• Create synchronized or read only collection
• and more...

23. enhanced for statement
• for (UnannType var : expr) stmt
• var : an element of expr
• expr : Collection or Array
• Get an element from expr iteratively
and set it to var, then do stmt

24. // Example #1:
// print any elements in the List
// to upper case every lines.
List<String> list = new ArrayList<>();
...
for (String s : list) {
// show elements (to upper case)
System.out.println(s.toUpperCase());
}

25. // Example #2:
// print any elements in the Set
// to upper case every lines.
Set<String> set = new HashSet<>();
...
for (String s : set) {
// show elements (as upper case)
System.out.println(s.toUpperCase());
}

26. Bulk operations

27. Basic concepts
Algorithm Data structures
Collections Collection
Map

28. Basic concepts
Algorithm Data structures
Collections Collection
Map
Stream

29. Collection and Stream API
Collection Stream
stream()
collect()
Data structure
Operators for
whole collection
Terminal
Operations
<<Export>>
<<Import>>

30. Stream as Set operators
(intermediate operations)
Method Role as Set operator
filter condition
map mapping values (a.k.a. production)
distinct reducing duplication
sorted sorting values
concat union with another set
limit truncation of values

31. Stream as Set operators
(terminal operations)
Method Role as Set operator
reduce general purpose totaling
min minimum of values
max maximum of values
count count of values
anyMatch whether any values match condition
allMatch whether all values match condition
noneMatch whether no value match condition

32. // Example
// Create a view from the result of Twitter4J
Twitter twitter =
TwitterFactory.getSingleton();
// snip
QueryResult result = twitter.search(query);
List<Status> statuses = result.getTweets();
List<Tweet> tweets =
statuses.stream() // to Stream (Set operations)
.filter(s -> s.getCreateAt().after(SOME_DAY))
.map(Tweet::new) // Convert Status to Tweet
.distinct() // Maybe, Stream has duplicates
.sort() // Sort by default order (prepare)
.limit(10) // Restrict 10 values from head
.collect(Collectors.toList); // List<Tweet>

33. Attentions

34. Concurrency
• Never synchronized (spec.)
• Make collections thread-safe:
• Synchronized by Collections
• Using concurrency collections
(java.util.concurrent.*) *recommend*

35. Old collections
• Vector, Hashtable, Stack
• Fixed to parts of collections:
e.g. Vector -> List, Hashtable -> Map
• Different behavior from standards:
• Synchronized
• Not allowed to add/put null

36. Appendix

37. Array
• Fixed Array
• Array
• Resizable Array
• Vector (now replaced ArrayList)

38. Definition of Array
• T [ ] identifier = new T [ size ] ;
• T : primitives or classes
• T [ ] : assumed a class
• e.g. String[] names = new String[3];

39. Initialization of Array
1. String[] names = new String[] {
“Able”, “Baker”, “Charlie” };
2. String[] names = new String[3];
String[0] = “Able”;
String[1] = “Baker”;
String[2] = “Charlie”;

40. Using Array
• Access by index:
String name = names[0]; // get “Able”
names[0] = “Alfa”; // set “Alfa”
• Obtain the length:
// Output ‘3’ to the console
System.out.println(names.length);

41. Array and Collection
• Array to List:
List<String> list =
Arrays.asList(names);
• List (Collection) to Array:
String[] names =
list.toArray(new String[list.size()]);

42. More Array.asList
• Arrays.asList method accepts variable
arguments, so …
List<String> list = Arrays.asList(
“Able”, “Baker”, “Charlie”);

43. Collections Framework
Beginners guide II
HASUNUMA Kenji
k.hasunuma@coppermine.jp