How to use map collection in java

Map collection is used to store key-value pairs. Here is how to use it: Create a Map: Use Map map = new HashMap(). Add elements: use map.put("key", "value"). Get elements: use String value = map.get("key"). Check for the existence of a key: use map.containsKey("key"). Remove elements: use map.remove("key"). Go over

Map collection in Java: usage method

Map collection is a powerful data structure in Java , used to store key-value pairs. It allows users to quickly retrieve values ​​using keys. Here's how to use a Map collection in Java:

1. Creating a Map collection

To create a Map collection, you can use the following syntax:

Map<K, V> map = new HashMap<>();

Where:

• K is the key type.
• V is a value type.
• HashMap is one of the implementation classes of Map collection.

2. Add elements

To add elements to the Map collection, you can use the put() method:

map.put("key", "value");

3. Get elements

To get the value in the Map collection, you can use the get() method:

String value = map.get("key");

4. Check Existence of key

To check whether a key exists in the Map collection, you can use the containsKey() method:

boolean containsKey = map.containsKey("key");

5. Delete element

To delete elements from the Map collection, you can use the remove() method:

map.remove("key");

6. Traverse the elements

To traverse the elements of the Map collection, you can use the entrySet() method. It returns a Set containing all key-value pairs in the Map collection:

for (Map.Entry<K, V> entry : map.entrySet()) {
    K key = entry.getKey();
    V value = entry.getValue();
}

Common implementation class of Map collection

• HashMap: Unordered and out of sync.
• TreeMap: Ordered and not synchronized.
• ConcurrentHashMap: Ordered and thread-safe.
• LinkedHashMap: Maintains insertion order and is thread-safe.

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