Map

✅ Map

• key ➕ value
• key: unique
• value: duplication possible
• no order

☑️ HashMap

• key ➕ value
• add, search value: O(1)
• no order
• get all: random
• O(1)
• must override hashCode() and equals() to use hash index

Map<String, Integer> studentMap = new HashMap<>();
studentMap.put("student1", 90);

//get value
studentMap.get("student1");
//get keys
Set<String> keys = studentMap.keySet();
//get values
Collection<Integer> values = studentMap.values();
//get key ➕ value
Set<Map.Entry<String, Integer>> entries = studentMap.entrySet();

☑️ LinkedHashMap

• HashMap ➕ linkedList(order)
• add, search value: O(1)
• get all: input order
• O(1)

☑️ TreeMap

• HashMap ➕ tree
• get all: key ascending order
• O(logN)

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