How to use map in java

Map is an interface that represents a collection of key-value pairs in Java and is used to store and search data efficiently. Its main uses include: storing data where each key corresponds to a unique value. Create unordered (HashMap), ordered (TreeMap), ordered and retain insertion order (LinkedHashMap) Maps. Add key-value pairs through the put() method, and obtain values ​​through the get() method. Traverse the Map using key sets (keySet()) and value sets (values()). Use the remove() method to delete key-value pairs.

Usage of Map in Java

What is Map?

Map is an interface in Java, which represents a collection of key-value pairs. The key is used to uniquely identify each value, while the value can be any object.

Purpose:

Map is mainly used to store data, where each key corresponds to a unique value. This makes finding data, updating data, and deleting data very efficient.

Create Map:

You can use the following methods to create a Map:

• HashMap: unordered and duplicates allowed key.
• TreeMap: Ordered and does not allow duplicate keys.
• LinkedHashMap: Ordered and allows duplicate keys, but preserves the order in which elements were inserted.

Add key-value pairs:

To add key-value pairs to the Map, you can use the put(key, value) method . If the key already exists, the existing value will be overwritten.

Get the value:

The value associated with a given key can be obtained using the get(key) method. If the key does not exist, returns null.

Traverse the Map:

You can use the keySet() and values() methods to traverse the keys and values ​​in the Map .

Delete key-value pairs:

You can use the remove() method to delete key-value pairs associated with a given key.

Example:

The following is a sample code that uses HashMap to create and use Map:

<code class="java">Map<String, Integer> ages = new HashMap<>();

ages.put("John", 30);
ages.put("Mary", 25);

System.out.println(ages.get("John")); // 输出：30

for (String key : ages.keySet()) {
    System.out.println(key + ": " + ages.get(key));
}</code>

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