Sets, Maps

1. Sets, Maps Sets, Maps AdvancedJava SoftUni Team Technical Trainers Software University http://softuni.bg

2. Table of Contents Sets – HashSet<E>, TreeSet<E>, LinkedHashSet<E> Maps – HashMap<K,V>, TreeMap<K, V>, LinkedHashMap<K, V>

3. Questions sli.do#9286

4. 3 7 -3 5 46 Sets HashSet<E>, TreeSet<E> and LinkedHashSet<E>

5. Sets in Java • A set keeps unique elements • Provides methods for adding/removing/searching elements • Offers very fast performance • HashSet<E> • The elements are randomly ordered • TreeSet<E> • The elements are ordered incrementally • LinkedHashSet<E> • The order of appearance is preserved

6. HashSet<E> – add() • HashSet<String> Pesho Pesho • Hash Function Alice Gosho

7. HashSet<E> – remove() • HashSet<String> • Hash Function Pesho Alice Alice Gosho

8. TreeSet<E> – add() • TreeSet<String> Pesho Pesho Alice Gosho

9. LinkedHashSet<E> – add() • LinkedHashSet<String> Pesho Pesho • Hash Function Alice Gosho

10. HashSet<E>andTreeSet<E> Exercises in class

11. иван гошо пешо 0845-346-356 2350-452-167 1255-377-131 Associative Arrays HashMap<Key, Value>

12. Associative Arrays (Maps) • Traditional array • Associative array key value 0 1 2 3 4 key value • Associative arrays are arrays indexed by keys • Not by the numbers 0, 1, 2, … • Hold a set of pairs <key,value>

13. HashMap<K, V> – add() • HashMap<String, String> Gosho Alice 0881-456-987 +359-899-55-592 Pesho 0881-123-987 • Hash Function • Key Value

14. HashMap<K, V> – remove() • HashMap<String, String> Pesho Gosho 0881-456-987 • Hash Function Pesho • 0881-123-987 Alice +359-899-55-592 • Key Value

15. TreeMap<K, V> – Example • TreeMap<String, String> Alice +359-899-55-592 Pesho 0881-123-987 • Key Value

16. LinkedHashMap<K, V> – add() • HashMap<String, String> Gosho Alice 0881-456-987 +359-899-55-592 Pesho 0881-123-987 • Hash Function • Key Value

17. Looping through dictionaries • Dictionary<string, string> Pesho Pesho 0881-123-987 0881-123-987 Gosho Gosho 0881-456-987 0881-456-987 Alice +359-899-55-592 Alice +359-899-55-592 • Key Value

18. HashMap<K, V>, TreeMap<K, V>, LinkedHashMap<K, V> • Have method size() – the number of key-value pairs • keySet() – a set of unique keys • values() – a collection of all values • Basic operations – put(), remove(), clear() • Boolean methods: • containsKey() – checks if a key is present in the dictionary • containsValue()–checks if a value is present in the dictionary

19. Associative Arrays Exercises in class

20. Summary HashSet<E>, TreeSet<E> and LinkedHashSet<E> hold unique elements and are very fast HashMap<K,V>, TreeMap<K, V> andLinkedHashMap<K, V> are an associative arrays where a value is accessed by its key

21. Sets, Maps https://softuni.bg/courses/java-fundamentals

22. License This course (slides, examples, demos, videos, homework, etc.)is licensed under the "Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International" license • Attribution: this work may contain portions from • "C# Fundamentals – Part 1" course by Telerik Academy under CC-BY-NC-SA license • "C# Fundamentals – Part 2" course by Telerik Academy under CC-BY-NC-SA license

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