Collection_List/ Set/ Map

✅ Collection Framework

framework to save, maange data in JAVA

✅ List

• duplicate element possible ⭕️
• has order in data
• insertion order ⭕️
• store null ⭕️
• has index
• can get() element by index

• 👍🏻 search, regularly access the element

• ArrayList
• LinkedList

✅ Set

• duplicate items impossible ❌
• has no order in data
• insertion order ❌
• only one null value

• 👍🏻 build collection of distinct items

• HashSet
• TreeSet

When to use set, instead of list?

when all items need to be unique

✅ Map

• key ➕ value are mapped
• hold pairs of keys and values
• 👍🏻 store data in key-value form
• duplicate key impossible ❌
• duplicate value possible ⭕️
• insertion order ❌
• allow single null key at most

• allow null value ⭕️

• HashMap
• TreeMap

        // Creating object for a Map.
        Map<String, Integer> map
            = new HashMap< String, Integer>();

        // Adding Elements using Map.
        map.put( "Rajat", 101);
        map.put("Shyam", 102);
        map.put("Rahul", 103);
        map.put("Krishna", 104);

☑️ ArrayList

• one direction pointer
• 👍🏻 fast in search

☑️ LinkedList

• double direction pointer
• 👍🏻 fast in insertion, deletion

ArrayList 🆚 LinkedList https://soheeparklee.github.io/posts/DB-3array-list-linked/

☑️ HashSet

// Instantiate an object of HashSet
HashSet<ArrayList> set = new HashSet<>();

// create ArrayList list1
ArrayList<Integer> list1 = new ArrayList<>();

// create ArrayList list2
ArrayList<Integer> list2 = new ArrayList<>();

// Add elements using add method
list1.add(1);
list1.add(2);
list2.add(1);
list2.add(2);
set.add(list1);
set.add(list2);

// print the set size to understand the
// internal storage of ArrayList in Set
System.out.println(set.size());

//result = 1
//two lists are considered equal if they have the same elements in the same order

• creates collection that stores elements in a hash table
• hash code, to function as object identifier
• insertion order not guaranteed ❌
• data duplication ❌

☑️ LinkedHashSet

• Linked list ➕ Hash Table
• insertion order guaranteed ⭕️(list의 특징)
• data duplication ❌(set의 특징)

☑️ TreeSet

• (default) if data can be compared, ordered in ascending otder
• data duplication ❌
• can implement comparable

☑️ HashMap

• insertion order not guaranteed ❌
• key duplication imossible ❌

☑️ LinkedHashMap

• insertion order guaranteed ⭕️
• key duplication imossible ❌

☑️ TreeMap

• save key-value on red-black tree
• (default) if data can be compared, ordered in ascending otder
• can implement comparable