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Anees Abdul
Anees Abdul

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Map Interface in JAVA

#programming #computerscience #java #beginners

In Java, the Map interface is part of the Java Collections Framework. A Map is used to store data in key–value pairs, where each key maps to exactly one value. Unlike lists, a Map does not store elements by index. Instead, it uses a key to retrieve the associated value.

Maps are very useful when we want to store and access data using a unique identifier.

Key Features of Map:

  • Stores data as key-value pairs
  • Keys are unique, but values can be duplicated
  • Part of java.util package
  • A single null value in the key is allowed, and multiple null values in the values are allowed

Since a Map is an interface, we cannot create its object directly. We must use a class that implements it..

Common Implementation of Map:

  1. HashMap
  2. LinkedHashMap
  3. TreeMap

What is HashMap:

  • Does not maintain insertion order
  • Allows one null key and multiple null values
  • Store elements in hash table structure 
HashMap<Integer,String> empMap= new HashMap<>();
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What is LinkedHashMap:

  • Maintain insertion order
  • Slightly slower than HashMap

What is TreeMap:

  • Stores elements in sorted order of keys
  • Does not allow null keys

** Methods in Map (with examples)**

put(K key, V value)

-Inserts or updates a key-value pair.

Map<String, Integer> map = new HashMap<>();
map.put("Alice", 30);
map.put("Bob", 25);
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get()

Retrieves the value associated with a key.

int age = map.get("Alice"); // 30
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containsKey()

Checks if the map contains a specific key.

boolean exists = map.containsKey("Bob"); // true
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remove()

Removes the mapping for a specific key.

map.remove("Bob")
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Size()

Used to return the number of key/value pairs available in the map

map,size();
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ContainsValue()

Cehcks if the map contains a specific values

map.containsValue(Value);// 
map.containsValue(101);
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isEmpty()

Checks whether the map is empty or not.

map.isEmpty();//false
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clear()

Removes all entries from the map

map.clear()
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keySet()

Returns a Set of all keys in the map.

Set<KeyType> keys = map.keySet();
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values()

Returns a Collection of all values in the map.

Collection<ValueType> values = map.values();
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entrySet()

Returns all key–value pairs as a Set of Map.Entry objects.

Set<Map.Entry<KeyType, ValueType>> entries = map.entrySet();
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| Method            | Purpose               |
| ----------------- | --------------------- |
| `put()`           | add key-value pair    |
| `get()`           | retrieve value        |
| `remove()`        | delete entry          |
| `containsKey()`   | check key             |
| `containsValue()` | check value           |
| `size()`          | number of entries     |
| `isEmpty()`       | check if map is empty |
| `clear()`         | remove all entries    |
| `keySet()`        | get all keys          |
| `values()`        | get all values        |
| `entrySet()`      | get key-value pairs   |
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