Hashmap in Java

Hashmap in Java is a data structure that allows you to store and retrieve data based on a key-value pair. It is implemented based on the hash table data structure, which provides constant-time performance for both adding and retrieving elements.

Declaring a Hashmap

To declare a Hashmap in Java, you need to import the java.util.HashMap package and create an instance of the HashMap class.

import java.util.HashMap;

HashMap<String, Integer> map = new HashMap<>();

Here, we are creating a Hashmap that stores keys as String and values as Integer.

Adding Elements to a Hashmap

To add elements to a Hashmap, you can use the put() method provided by the HashMap class.

map.put("One", 1);
map.put("Two", 2);
map.put("Three", 3);

Here, we are adding three elements to our HashMap.

Retrieving Elements from a Hashmap

To retrieve elements from a Hashmap, you can use the get() method provided by the HashMap class.

int value = map.get("Two");

Here, we are retrieving the value of the key "Two", which is 2.

Removing Elements from a Hashmap

To remove elements from a Hashmap, you can use the remove() method provided by the HashMap class.

map.remove("Three");

Here, we are removing the key-value pair associated with the key "Three".

Conclusion

Hashmap in Java is a powerful data structure that allows you to store and retrieve data based on a key-value pair. It provides constant-time performance for both adding and retrieving elements, making it an ideal choice for many applications. If you are interested in learning more about Hashmap, I recommend reading the Java documentation or taking an online course on data structures and algorithms.