How do I use HashMap in Java?

How do I use HashMap in Java?

A HashMap in Java is a part of the Java Collections Framework. It stores data in key-value pairs. You can add, remove, and access elements using keys.

Can you show me an example of adding elements to a HashMap?

Sure! Here's a simple example:

import java.util.HashMap;

public class Main {
    public static void main(String[] args) {
        HashMap<String, Integer> map = new HashMap<>();
        map.put("Apple", 1);
        map.put("Banana", 2);
        System.out.println(map);
    }
}

This code creates a HashMap and adds two key-value pairs.

What happens if I try to add a duplicate key?

If you add a duplicate key, the new value will overwrite the existing value associated with that key. For example, if you do map.put("Apple", 3);, the value for "Apple" will change from 1 to 3.

How can I iterate over the keys in a HashMap?

You can use a for-each loop to iterate over the keys. Here's an example:

for (String key : map.keySet()) {
    System.out.println(key + " : " + map.get(key));
}